JP2532306B2 - Continuous casting method - Google Patents

Description

【発明の詳細な説明】Detailed Description of the Invention

【０００１】[0001]

【産業上の利用分野】本発明は連続鋳造鋳片の厚み中心
部に見られる不純物元素、即ち鋼鋳片の場合には硫黄、
燐、マンガン等の偏析を防止し、均質な金属を得ること
のできる連続鋳造法に関するものである。BACKGROUND OF THE INVENTION The present invention relates to an impurity element found in the center of thickness of a continuously cast slab, namely sulfur in the case of a steel slab.
The present invention relates to a continuous casting method capable of preventing the segregation of phosphorus, manganese, etc. and obtaining a homogeneous metal.

【０００２】[0002]

【従来の技術】近年、海洋構造物、貯槽、石油およびガ
ス運搬用鋼管、高張力線材などの材質特性に対する要求
は厳しさを増しており、均質な鋼材を提供することが重
要課題となっている。元来鋼材は、断面内において均質
であるべきものであるが、鋼は一般に硫黄、燐、マンガ
ン等の不純物元素を含有しており、これらが鋳造過程に
おいて偏析し部分的に濃化するため鋼が脆弱となる。特
に近年、生産性や歩留向上および省エネルギー等の目的
のために連続鋳造法が一般に普及しているが、連続鋳造
により得られる鋳片の厚み中心部近傍には通常顕著な成
分偏析が観察される。2. Description of the Related Art In recent years, the demands on the material properties of offshore structures, storage tanks, steel pipes for transporting oil and gas, high-strength wire rods, etc. have become more severe, and it is an important issue to provide homogeneous steel rods. There is. Originally, steel should be homogeneous in cross section, but steel generally contains impurity elements such as sulfur, phosphorus, and manganese, and these segregate and partially concentrate during the casting process. Becomes vulnerable. In particular, in recent years, continuous casting has been widely used for the purpose of improving productivity, yield improvement, energy saving, etc., but generally significant component segregation is observed in the vicinity of the thickness center of the slab obtained by continuous casting. It

【０００３】上記した成分偏析は最終成品の均質性を著
しく損ない、製品の使用過程や線材の線引き工程等で鋼
に作用する応力により亀裂が発生するなど重大欠陥の原
因になるため、その低減が切望されている。かかる成分
偏析は凝固末期に残溶鋼が凝固収縮力等により流動し、
固液界面近傍の濃化溶鋼を洗いだし、残溶鋼が累進的に
濃化していくために発生すると考えられている。従って
成分偏析を防止するには、残溶鋼の流動原因を取り除く
ことが肝要である。The above-mentioned component segregation significantly impairs the homogeneity of the final product, and causes serious defects such as cracks due to stress acting on the steel during the use of the product or the wire drawing process of the wire rod. Coveted. Such component segregation causes residual molten steel to flow at the end of solidification due to solidification shrinkage force,
It is thought that this occurs because the concentrated molten steel near the solid-liquid interface is washed out and the residual molten steel is progressively concentrated. Therefore, in order to prevent the segregation of the components, it is important to eliminate the cause of the flow of the residual molten steel.

【０００４】このような流動原因としては、凝固収縮に
起因する流動のほか、ロール間の鋳片バルジングやロー
ルアライメント不整に起因する流動等があるが、これら
のうち最も重大な原因は凝固収縮であり、偏析を防止す
るには、これを補償する量だけ鋳片を圧下することが必
要である。鋳片を圧下することにより偏析を改善する試
みは従来より行われており、連続鋳造工程において鋳片
中心部温度が液相線温度から固相線温度に至るまでの
間、鋳片の凝固収縮を補償する量以上の一定割合で圧下
する方法が知られている。As such a cause of flow, in addition to a flow caused by solidification shrinkage, there is a slab bulging between rolls and a flow caused by roll alignment irregularity, and the most serious cause is solidification shrinkage. Therefore, in order to prevent segregation, it is necessary to roll down the slab by an amount that compensates for this. Attempts have been made to reduce segregation by rolling down the slab, and in the continuous casting process, the solidification shrinkage of the slab is observed during the period from the liquidus temperature to the solidus temperature of the slab center. There is known a method of rolling down at a constant rate equal to or more than the amount compensating for.

【０００５】しかしながら、従来の連続鋳造法は、条件
によっては偏析改善効果が殆ど認められなかったり、場
合によっては、偏析がかえって悪化する等の問題があ
り、成分偏析を充分に改善することは困難であった。本
発明者等はかかる従来法の問題の発生原因について種々
調査した結果、従来法の偏析改善効果が認められなかっ
たり、あるいは偏析がかえって悪化することがおこるの
は基本的に圧下すべき凝固時期とその範囲が不適正であ
ることを突き止めた。However, the conventional continuous casting method has a problem that the segregation improving effect is hardly recognized depending on the conditions, and in some cases, the segregation rather deteriorates, and it is difficult to sufficiently improve the component segregation. Met. As a result of various investigations by the inventors on the cause of the problems of the conventional method, the segregation improving effect of the conventional method is not recognized, or the segregation rather deteriorates. And found that the range was inappropriate.

【０００６】このような知見に基づき、本発明者等は、
先に特開昭６２−２７５５５６号公報において、鋳片の
中心部が固相率０．１ないし０．３に相当する温度とな
る時点から流動限界固相率に相当する温度となる時点ま
での領域を単位時間当り０．５mm／分以上２．５mm／分
未満の割合で連続的に圧下し、鋳片中心部が流動限界固
相率に相当する温度となる時点から固相線温度となるま
での領域は実質的に圧下を加えないようにした連続鋳造
方法を提案した。Based on such knowledge, the present inventors have
In Japanese Unexamined Patent Publication (Kokai) No. 62-275556, the time from the time when the central portion of the slab reaches the temperature corresponding to the solid fraction of 0.1 to 0.3 to the time corresponding to the temperature corresponding to the fluidity limit solid fraction. The region is continuously reduced at a rate of 0.5 mm / min or more and less than 2.5 mm / min per unit time, and the solidus temperature is reached from the time when the temperature at the center of the slab reaches the temperature corresponding to the fluidity limit solid fraction. A continuous casting method was proposed in which no reduction was applied to the regions up to.

【０００７】さらに本発明者等は、数多くの実験を推進
することにより、先に特願平１−１２０２９５号におい
て提示したごとく、濃化溶鋼が激しく鋳片の中心部に集
積する凝固時期が存在し、この濃化溶鋼の集積時期の流
動を防止することが偏析改善にとって最も重要であり、
また濃化溶鋼の集積量が特に多い凝固時期は凝固組織に
よって異なることを知見した。Further, the inventors of the present invention promoted many experiments, and as shown in Japanese Patent Application No. 1-120295, there is a solidification time when the concentrated molten steel is violently accumulated in the center of the slab. However, preventing the flow of this concentrated molten steel during the accumulation period is the most important for improving the segregation,
It was also found that the solidification timing at which the amount of concentrated molten steel is particularly large differs depending on the solidification structure.

【０００８】この結果に基づき偏析をさらに改善する軽
圧下法について研究した結果、凝固末期に少なくとも１
対のロールにより鋳片を圧下しつつ引き抜く溶融金属の
連続鋳造法において、上面等軸晶率が５％未満の場合、
鋳片中心部の温度が固相率０．２５、好ましくは０．３
５に相当する位置から流動限界固相率に相当する位置ま
での凝固時期範囲の任意の位置、好ましくは該凝固時期
範囲内の上流側に少なくとも１対のロールを設置し、該
凝固時期範囲内の全凝固収縮量を補償する量を圧下し、
また上面等軸晶率が５％以上の場合、鋳片中心部の温度
が固相率０．１好ましくは０．１５に相当する位置から
流動限界固相率に相当する位置までの凝固時期範囲の任
意の位置、好ましくは該凝固時期範囲内の上流側に少な
くとも１対のロールを設置し、該凝固時期範囲内の全凝
固収縮量を補償する量を圧下することを特徴とする圧下
範囲を小さくすることが可能な簡便で効率的な軽圧下法
を提案するに至った。Based on this result, as a result of research on a light reduction method for further improving segregation, it was found that at least 1 at the end of coagulation.
In the continuous casting method of molten metal in which the slab is pulled down while rolling down by a pair of rolls, when the upper equiaxed crystal ratio is less than 5%,
The temperature at the center of the slab is 0.25, preferably 0.3
At least one pair of rolls is installed at any position in the solidification time range from the position corresponding to 5 to the position corresponding to the flow limit solid phase ratio, preferably at the upstream side within the solidification time range, The amount that compensates for the total coagulation shrinkage of
Further, when the equiaxed crystal ratio of the upper surface is 5% or more, the solidification timing range from the position where the temperature at the center of the slab corresponds to the solid fraction 0.1, preferably 0.15, to the position corresponding to the flow limit solid fraction Of at least one pair of rolls, preferably at the upstream side within the coagulation timing range, and reducing the amount that compensates for the total coagulation contraction amount within the coagulation timing range. We have come to propose a simple and efficient light reduction method that can be made small.

【０００９】しかしながら連続鋳造作業においては、鍋
交換、最トップ処理あるいは突発的なトラブルに起因し
た鋳造速度の減速、停止等が頻繁に発生するため、鋳片
が圧下帯に到達するのが遅れたり、圧下帯内で鋳造速度
が減速あるいは停止した非定常鋳片の発生をゼロにする
ことは非常に難しく、これら非定常部鋳片の偏析は定常
部と比べ悪化が認められる。However, in the continuous casting work, since the pot speed is frequently changed and the casting speed is slowed down or stopped due to sudden top troubles or sudden troubles, the slab may be delayed in reaching the draft zone. It is very difficult to eliminate the occurrence of unsteady slabs in which the casting speed has slowed or stopped in the rolling zone, and segregation of these unsteady slabs is worse than in the steady part.

【００１０】このような鋳造速度の変動のために軽圧下
の偏析改善効果が不充分な鋳片を出発材とする線材のト
ラブルを防止するためには、偏析が最も悪い部位におい
てもトラブルの発生を避けるべく分塊加熱条件を高温、
長時間になるように選択する必要があるが、このため偏
析が良好な定常部鋳片に対してオーバーアクションとな
り、また高温加熱においては、加熱炉における鉄ロスお
よび脱炭層の発生などの歩留の低減や、作業性の悪化な
どの問題が発生する。[0010] In order to prevent the trouble of the wire rod starting from a cast piece having a insufficient segregation improving effect under a light reduction due to such a variation of the casting speed, the trouble occurs even in the portion where the segregation is the worst. To avoid lumpy heating conditions high temperature,
Although it is necessary to select it for a long period of time, this causes an over-action for a segregated slab with good segregation, and during high-temperature heating, yield such as iron loss and decarburized layer generation in the heating furnace occurs. And the workability is deteriorated.

【００１１】このような問題点を改善するためには定常
部鋳片のさらなる偏析改善と同時に非定常部の偏析悪化
鋳片を分離選択する必要がある。本発明者等はこれら偏
析悪化鋳片の分離選択方法として、先に当該鋳片の圧下
帯通過速度と圧下帯入口ロールに到達した時の凝固時期
により軽圧下による偏析改善効果が不充分な非定常部鋳
片を分離選択する方法（提案法という）を特許出願によ
り提案するに至った。In order to improve such problems, it is necessary to further improve the segregation of the slab of the steady part and simultaneously select the slab of the non-steady part with deterioration of the segregation. The present inventors, as a separation selection method of these segregation deteriorated slab, the segregation improvement effect by light reduction is insufficient due to the rolling speed of the slab and the solidification timing when it reaches the pressing zone inlet roll. We have proposed a patent application for a method for selecting and selecting a stationary part slab (referred to as the proposed method).

【００１２】[0012]

【発明が解決しようとする課題】しかし上記した提案法
では、図１に示すごとく、鋳造速度が減速、停止した時
に連鋳機内に位置していた鋳片のほとんど全長が偏析が
悪い非定常部鋳片と判定され、必ずしも歩留良好な判定
方法でなく、さらに精度良く偏析悪化鋳片を判定し、歩
留を改善することが重要課題である。However, in the above proposed method, as shown in FIG. 1, almost all the length of the cast piece located in the continuous casting machine when the casting speed is reduced or stopped is unsteady in which the segregation is bad. It is determined that the slab is a slab, which is not necessarily a good yield determination method, and it is an important issue to more accurately determine a segregation-deteriorated slab and improve the yield.

【００１３】本発明者等はかかる問題を解決するため、
鋳造速度が変動した鋳片の偏析決定要因の研究を進めた
結果、軽圧下による偏析改善効果が充分で偏析が良好な
鋳片部位を選び出し、分塊加熱条件を低温短時間にする
ことが可能な連続鋳造法を提供するに至った。In order to solve such a problem, the present inventors have
As a result of research on the segregation determining factors of the slab with varying casting speed, it is possible to select the slab that has a sufficient segregation improvement effect by light reduction and has good segregation, and the slab heating conditions can be kept at low temperature for a short time. Has provided a continuous casting method.

【００１４】[0014]

【課題を解決するための手段】本発明の要旨とするとこ
ろは下記のとおりである。 （１） １対以上のロールにより、鋳片を圧下しつつ引
き抜く溶融金属の連続鋳造法において、鋳造速度の減速
および停止にともない発生する偏析悪化鋳片か否かを、
当該鋳片が、凝固時期Ａから凝固時期Ｂまでの凝固時期
範囲の平均鋳造速度及び当該鋳片の圧下開始凝固時期Ｃ
により判定し、その判定結果に応じて、当該鋳片の分塊
工程での加熱条件を決定することを特徴とする連続鋳造
法。 The subject matter of the present invention is as follows. (1) In a continuous casting method of molten metal in which a slab is drawn while being pressed by a pair of rolls or more, whether or not the segregation deteriorated slab is generated as the casting speed is reduced and stopped ,
The slab has a solidification time from solidification time A to solidification time B
Average casting speed in the range and rolling start solidification timing C of the cast piece
According to the result of the judgment,
Continuous casting characterized by determining heating conditions in the process
Law.

【００１５】ただし、凝固時期Ａ、凝固時期Ｂ、圧下開
始凝固時期Ｃは、予め決められた数値であ り、中心固相
率、シェル厚など鋳片凝固の進捗度を示す指標で示す。 （２） 各鋳片部位毎の偏析データと凝固時期範囲Ａか
らＢ間の平均鋳造速度を見比べて偏析最悪化部位に最も
良く対応する前記平均鋳造速度推移を表す凝固時期Ａ、
凝固時期Ｂを採用することを特徴とする前項１記載の連
続鋳造法。 However, coagulation timing A, coagulation timing B, reduction opening
Start coagulation time C is Ri numerical der previously determined, the center solid phase
The rate, shell thickness, and other indicators are used to indicate the progress of solidification of cast slabs. (2) Segregation data for each cast piece and solidification time range A
Compare the average casting speed between B and B
Solidification time A that represents the transition of the average casting speed that corresponds well,
Coupling time B is adopted, so that
Sequential casting method.

【００１６】以下本発明をさらに細述する。本発明者等
は図２の例で示すような鋳造速度が減速および停止する
場合の偏析決定要因について研究した結果、偏析が悪化
している鋳片は、当該鋳片が凝固する間の特定な凝固時
期範囲Ａ〜Ｂの平均鋳造速度が減速した鋳片と当該鋳片
の圧下開始時期Ｃが遅れた鋳片であり、偏析悪化鋳片は
当該鋳片が凝固時期Ａから凝固時期Ｂに凝固する間の平
均鋳造速度と圧下開始時期Ｃにより精度良く分離できる
ことを知見し、本発明をなしとげた。凝固時期および圧
下開始時期は、ここでは、中心固相率で表しているが、
シェル厚、未凝固厚などで表してもよい。また、偏析悪
化鋳片と判定される鋳片長さは図３に示すごとく、凝固
時期Ａ、Ｂの中心固相率として０．１５、０．３を採用
した場合より、０．１、０．４を採用した方が大きく、
ＡとＢの差が大きいほど長くなることがわかる。この傾
向を利用し、各鋳片部位毎の偏析データと凝固時期Ａ、
Ｂ間の平均鋳造速度を見比べて、偏析最悪化部位に最も
よく対応するような前記平均鋳造速度の変化を表しうる
Ａ、Ｂを予め決定しておく。図３においては、その結果
がＡ＝０．１５、Ｂ＝０．３である。 The present invention will be described in more detail below. As a result of research on the segregation determining factors when the casting speed slows down and stops as shown in the example of FIG. 2, the present inventors have found that a slab with poor segregation has a specific value during solidification of the slab. A slab whose average casting speed in the solidification timing range A to B has been slowed and a slab with a reduction start timing C of the slab being delayed, and a slab with deteriorated segregation solidifies from the solidification timing A to the solidification timing B. The present invention has been accomplished by discovering that the separation can be performed with high accuracy by the average casting speed and the rolling start time C during the heating. Coagulation timing and pressure
The lower start time is represented by the central solid fraction here,
It may be expressed as a shell thickness, an unsolidified thickness, or the like. Also, segregation evil
As shown in Fig. 3, the length of the slab that is judged to be a slab is solidified.
0.15 and 0.3 are adopted as the central solid fractions of time A and B
When adopting 0.1, 0.4 is larger than when
It can be seen that the larger the difference between A and B, the longer the length. This inclination
Segregation data and solidification time A for each cast part,
Compare the average casting speed between B,
Can represent changes in the average casting speed that correspond well
A and B are determined in advance. In Figure 3, the result
Is A = 0.15 and B = 0.3.

【００１７】偏析悪化鋳片を精度良く分離して、かつ偏
析悪化鋳片と判定される鋳片長さを短くするためには、
偏析が最も悪い鋳片のみを分離できるよう、管理すべき
凝固時期範囲Ａ〜Ｂを狭くすればよい。Ａ，Ｂとしてど
の凝固時期を採用するかは、得られた鋳片の偏析程度や
偏析のバラツキおよび分塊圧延条件等の工程能力により
異なると考えられ、全工程を考慮した場合のメリットに
よって決定する必要がある。In order to accurately separate the segregation-deteriorated slab and shorten the slab that is determined to be the segregation-deteriorated slab,
The solidification time range A to B to be controlled may be narrowed so that only the cast product having the worst segregation can be separated. It is considered that which solidification time is adopted as A and B depends on the segregation degree of the obtained cast piece, the variation in segregation, and the process capability such as slab rolling conditions. It is determined by the merits when considering all processes. There is a need to.

【００１８】以上に示した本発明の方法によれば、図３
に示すごとく偏析が悪化している鋳片部位はＡ、Ｂの値
を適正にすることにより精度よく分離することができ
る。その結果、図４に示すごとく当該鋳片が圧下帯を通
過する時の平均鋳造速度と圧下帯に到達した時の凝固時
期により選択する従来法より、偏析悪化鋳片と判定する
鋳片長さが短くなり、偏析が良好な鋳片を歩留りよく分
離することが可能になる。 According to the method of the present invention described above, FIG.
The values of A and B are for the slabs where segregation is worse as shown in
Can be separated accurately by adjusting
It As a result, as shown in FIG. 4, the segregation deteriorated slab is determined by the conventional method that is selected according to the average casting speed when the slab passes through the reduction zone and the solidification timing when the slab reaches the reduction zone.
The slab length is shortened, and slabs with good segregation are separated with good yield.
It becomes possible to separate.

【００１９】このように選択した偏析良好な鋳片の分塊
圧延の加熱条件を低温、短時間にすることにより使用エ
ネルギーおよび鉄歩留の大幅な節約が可能になる。な
お、鋳片の凝固時期は中心固相率、シェル厚、未凝固厚
あるいは未凝固率で定量化することが可能であるが、こ
こでは特願平２−７８９４０号に示したごとく、偏析の
生成に最も影響をおよぼすと考えられる鋳片中心部の通
液抵抗の増加と関係があると推定される中心固相率で定
量化した。By thus setting the heating conditions for the slabbing of the slab with favorable segregation selected at a low temperature for a short time, it is possible to greatly save the energy used and the iron yield. The solidification timing of the slab can be quantified by the central solid phase ratio, shell thickness, unsolidified thickness or unsolidified ratio, but here, as shown in Japanese Patent Application No. 2-78940, segregation It was quantified by the central solid fraction, which is estimated to be related to the increase of liquid flow resistance in the center of the slab, which is considered to have the greatest effect on the formation.

【００２０】中心固相率は１）式の例のごとく、鋳片中
心部の温度の関数として算出することが可能で、中心部
に存在する固相の割合である。鋳片中心部の温度は操業
条件に基づき伝熱計算によりあらかじめ計算するか、ま
たは鋳造中に当該鋳片の冷却や鋳造速度等の条件に基づ
き計算する。凝固時期を示す１つの指標である中心固相
率は鋳造速度、冷却条件、鋳片サイズ、鋼種が決まれ
ば、特願平１−１２１４８７号に示したごとく凝固時間
の関数であり、中心固相率は各鋳片位置の注入時の時刻
と連鋳機の各位置に至った時の時刻の差分として算出し
た凝固時間から簡単に計算できる。また同じく凝固時間
の関数であるシェル厚、未凝固厚、未凝固率に容易に換
算することができる。また、当該鋳片の凝固時期がＡか
らＢに凝固する凝固時期範囲の平均鋳造速度は２）式に
より決定する。 鋳片の中心固相率＝（Ｔｌ−Ｔ）／（Ｔｌ−Ｔｓ） １） Ｔｌ：溶鋼の液相線温度（℃） Ｔｓ：溶鋼の固相線温度（℃） Ｔ ：鋳片の中心部温度（℃） 凝固時期がＡからＢに凝固する間の平均鋳造速度＝Ｌ／ｔ （m/min ） ２） Ｌ：当該鋳片がＡからＢに凝固する間の当該鋳片の移動長さ (m） ｔ：当該鋳片がＡからＢに凝固する凝固時間 (min) 次ぎに本発明を実施例により説明する。The central solid fraction can be calculated as a function of the temperature of the central portion of the slab as in the case of the equation (1), and is the proportion of the solid phase present in the central portion. The temperature of the central portion of the slab is calculated in advance by heat transfer calculation based on the operating conditions, or is calculated based on conditions such as cooling of the slab and casting speed during casting. Central solid phase, which is one indicator of the time of solidification
Rate is determined by casting speed, cooling conditions, slab size, steel type
For example, coagulation time as shown in Japanese Patent Application No. 1-1212487.
The central solid fraction is the time of injection at each slab position.
And the time when each position of the continuous casting machine is reached.
It can be easily calculated from the solidification time. The shell thickness is a function of the same clotting time, unsolidified thickness, it can easily be converted into unsolidified rate. Further, the average casting speed in the solidification timing range in which the solidification timing of the slab solidifies from A to B is determined by the equation 2). Core solid fraction of cast slab = (Tl-T) / (Tl-Ts) 1) Tl: Liquidus temperature of molten steel (° C) Ts: Solidus temperature of molten steel (° C) T: Center of cast slab Temperature (° C) Solidification time Average casting rate during solidification from A to B = L / t (m / min) 2) L: Moving length of the slab while the slab solidifies from A to B (m) t: Solidification time for the cast piece to solidify from A to B (min) Next, the present invention will be described with reference to examples.

【００２１】[0021]

【実施例】実施例１ 試験を実施した連鋳機の概略を図５に示し、鋳造した溶
鋼組成の代表例を表１に示す。偏析が悪化している鋳片
は、図３に示すごとく、当該鋳片が中心固相率で０．１
５から０．３に凝固する間の平均鋳造速度が定常部より
減速した鋳片と、当該鋳片の圧下開始が遅れた鋳片であ
る。また、図６には全量同一分塊加熱条件（従来より低
温、短時間）で圧延した場合の線材偏析が良好となる条
件を示す。線材偏析の悪化が認められるのは当該鋳片位
置が中心固相率で０．１５から０．３に凝固する間の平
均鋳造速度が定常部より減速した鋳片と、当該鋳片の圧
下開始中心固相率が０．１９以上の鋳片である。本実施
例により分離した偏析悪化非定常部鋳片の分塊加熱条件
を従来通りとし、偏析良好な定常部鋳片の分塊加熱条件
を従来より低温、短時間にした場合の線材偏析を図７に
示す。線材偏析は全量良好となり、従来法と比べ偏析の
ない均質な鋼材が低エネルギーで得られることが証明さ
れた。EXAMPLES Example 1 An outline of a continuous casting machine used for the test is shown in FIG. 5, and a typical example of the composition of the molten steel cast is shown in Table 1. As shown in FIG. 3, the slab with the deteriorated segregation has a central solid fraction of 0.1.
It is a slab in which the average casting speed during solidification from 5 to 0.3 is slower than in the steady part, and a slab in which the rolling start of the slab is delayed. Further, FIG. 6 shows a condition in which the wire segregation becomes good when the whole amount is rolled under the same agglomeration heating conditions (lower temperature and shorter time than conventional). Deterioration of wire rod segregation is observed in the slab where the average casting speed slows down from the steady part while the slab position solidifies from 0.15 to 0.3 in the central solid fraction, and the start of reduction of the slab A slab having a central solid fraction of 0.19 or more. The segregation deterioration of the segregation deterioration unsteady part separated according to the present example is the conventional slab heating condition, and the segregation good slab heating condition is lower than the conventional slab heating condition. 7 shows. It was proved that the segregation of the wire rod was good, and that a homogeneous steel without segregation could be obtained with low energy compared with the conventional method.

【００２２】実施例２ 本実施例で鋳造した溶鋼組成の代表例を表２に示す。図
８に示すごとく偏析が悪化している鋳片部位に対応して
いるのは、当該鋳片が中心固相率で０．２５から０．５
に凝固する間の平均鋳造速度が定常部より減速した鋳片
と、当該鋳片が圧下帯に到達した時の中心固相率が遅れ
た鋳片である。図９では分塊加熱条件を低温、短時間に
した場合の線材偏析が良好となる条件を示す。当該鋳片
の凝固状態が中心固相率で０．２４〜０．５に凝固する
間の平均鋳造速度が減速した鋳片と、当該鋳片が圧下帯
入口ロールに到達した時の中心固相率が０．２４以上の
鋳片の偏析の悪化が認められる。実施例１の場合と同じ
ように、本実施例により分離した偏析悪化非定常部鋳片
の分塊加熱条件を従来通りとし、偏析良好な定常部鋳片
の分塊圧延条件を従来より低温、短時間にした結果、線
材偏析は全量良好となり、偏析のない均質な鋼材が従来
法と比べより少ないエネルギーで効率的に得られること
が証明された。Example 2 Table 2 shows a typical example of the composition of molten steel cast in this example. As shown in FIG. 8, the slab where the segregation deteriorates corresponds to the slab having a central solid fraction of 0.25 to 0.5.
A slab with an average casting speed slowing down from the steady part during solidification and a slab with a delayed central solid fraction when the slab reaches the reduction zone. FIG. 9 shows conditions under which the wire segregation becomes good when the slab heating conditions are low temperature and short time. A slab whose average casting speed is reduced while the solidification state of the slab solidifies to 0.24 to 0.5 at the central solid fraction, and a central solid phase when the slab reaches the reduction zone inlet roll Deterioration of segregation of slabs with a rate of 0.24 or more is recognized. As in the case of Example 1, the slab heating conditions of the segregation-deteriorated non-steady part cast separated according to the present example were set to the conventional values, and the segregation good slab rolling conditions of the steady part slab were set to a lower temperature than the conventional values. As a result of shortening the time, it was proved that the segregation of the wire rod was good in its entirety and that a homogenous steel material without segregation could be efficiently obtained with less energy as compared with the conventional method.

【００２３】実施例３ 表３に種々な鋼種、凝固組織の場合について、鋳造速度
の減速停止により偏析が悪化した当該鋳片の凝固時期範
囲および当該鋳片の圧下開始凝固時期を示す。表３の結
果に基づき鋳造速度の減速にともない発生する偏析改善
効果が不充分な鋳片部位を選択し、偏析良好部位の分塊
圧延条件を低温、短時間に改善することが可能になる。Example 3 Table 3 shows, for various steel types and solidification structures, the solidification timing range of the cast slab in which segregation deteriorated due to the deceleration stop of the casting speed and the rolling start solidification timing of the cast slab. Based on the results of Table 3, it becomes possible to select a cast piece site having an insufficient segregation improving effect which occurs with a decrease in casting speed, and improve the slabbing condition of a good segregation site at a low temperature in a short time.

【００２４】[0024]

【表１】 [Table 1]

【００２５】[0025]

【表２】 [Table 2]

【００２６】[0026]

【表３】 [Table 3]

【００２７】[0027]

【発明の効果】本発明により鋳造速度の変動に伴い発生
する軽圧下の偏析改善効果が充分な鋳片と不充分な鋳片
を分離することにより、偏析レベルに応じた分塊圧延条
件および工程が選択でき、従来より少ないエネルギーで
歩留良く均質な鋼材を得ることが可能な、連続鋳造法が
提供される。EFFECTS OF THE INVENTION According to the present invention, by separating a slab with a sufficient segregation improving effect under a light reduction caused by a variation in casting speed and a slab with an insufficient segregation, slab rolling conditions and processes depending on the segregation level are obtained. Is provided, and a continuous casting method is provided that enables obtaining a homogeneous steel material with a low yield and a good yield.

【図面の簡単な説明】[Brief description of drawings]

【図１】図１は従来法において偏析悪化鋳片と判定され
る鋳片範囲を示す図である。FIG. 1 is a view showing a range of a cast piece determined to be a segregation-deteriorated cast piece in a conventional method.

【図２】図２は鋳造速度の変動例を示す図である。FIG. 2 is a diagram showing an example of fluctuations in casting speed.

【図３】図３は偏析が悪化している鋳片と対応する当該
鋳片がＡ〜Ｂに凝固する間の平均鋳造速度を示す図であ
る。FIG. 3 is a diagram showing an average casting speed during solidification of A to B corresponding to a slab in which segregation is deteriorated.

【図４】図４は偏析悪化鋳片と判定される鋳片長さの従
来法との比較を示す図である。FIG. 4 is a diagram showing a comparison of a slab length determined as a segregation-deteriorated slab with a conventional method.

【図５】図５は連鋳機の概略図である。FIG. 5 is a schematic view of a continuous casting machine.

【図６】図６は実施例１で全量低温、短時間分塊加熱を
実施した場合の線材偏析が良好となる条件を示す図であ
る。FIG. 6 is a view showing conditions under which wire segregation becomes good in the case of performing lump heating for a short time at a low temperature in Example 1.

【図７】図７は実施例１で選択した偏析良好部位の分塊
加熱条件を低温、短時間とし、偏析悪化鋳片を従来通り
とした線材偏析のレベルを示す図である。FIG. 7 is a diagram showing the level of segregation of wire rods in which the segregation heating conditions for the segregation-favored portion selected in Example 1 were low temperature and short time, and the segregation-deteriorated cast piece was conventional.

【図８】図８は偏析が悪化している鋳片と対応する当該
鋳片がＡ（Ａ′）〜Ｂに凝固する間の平均鋳造速度（実
施例２の場合）を示す図である。FIG. 8 is a diagram showing an average casting speed (in the case of Example 2) during solidification of a cast piece corresponding to a cast piece having deteriorated segregation into A (A ′) to B.

【図９】図９は実施例２で全量低温、短時間分塊加熱を
実施した場合の線材偏析が良好となる軽圧下条件を示す
図である。FIG. 9 is a diagram showing a light reduction condition in which wire segregation becomes good in the case of performing lump heating at low temperature for a short time in Example 2;

───────────────────────────────────────────────────── フロントページの続き (72)発明者 久保 勝彦 千葉県君津市君津１番地 新日本製鐵株 式会社 君津製鐵所内 (56)参考文献 特開 平２−280952（ＪＰ，Ａ) ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Katsuhiko Kubo 1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel Co., Ltd. Kimitsu Works (56) Reference JP-A-2-280952 (JP, A)

Claims (2)

(57)【特許請求の範囲】(57) [Claims] 【請求項１】 １対以上のロールにより、鋳片を圧下し
つつ引き抜く溶融金属の連続鋳造法において、鋳造速度
の減速および停止にともない発生する偏析悪化鋳片か否
かを、当該鋳片が、凝固時期Ａから凝固時期Ｂまでの凝
固時期範囲の平均鋳造速度及び当該鋳片の圧下開始凝固
時期Ｃにより判定し、その判定結果に応じて、当該鋳片
の分塊工程での加熱条件を決定することを特徴とする連
続鋳造法。 ただし、凝固時期Ａ、凝固時期Ｂ、圧下開始凝固時期Ｃは、予め
決められた数値であ り、中心固相率、シェル厚など鋳片
凝固の進捗度を示す指標で示す。 1. In a continuous casting method for molten metal in which a slab is drawn while being rolled down by one or more pairs of rolls, whether or not the slab is a segregation-deteriorated slab that is generated as the casting speed is reduced and stopped.
The slab is solidified from solidification time A to solidification time B.
Average casting speed in the solid time range and rolling start solidification of the slab
Judgment is made according to the timing C, and the cast slab according to the judgment result.
Series, characterized in that it determines the heating conditions in the agglomeration process of
Sequential casting method. However, the coagulation timing A, the coagulation timing B, and the rolling start coagulation timing C are
Numerical der that is determined is, the center solid phase ratio, such as shell thickness slab
It is shown by an index showing the progress of coagulation. 【請求項２】 各鋳片部位毎の偏析データと凝固時期範
囲ＡからＢ間の平均鋳造速度を見比べて偏析最悪化部位
に最も良く対応する前記平均鋳造速度推移を表す凝固時
期Ａ、凝固時期Ｂを採用することを特徴とする請求項１
記載の連続鋳造法。 2. Segregation data and solidification timing range for each cast piece site
Comparing the average casting speed between the areas A and B, the segregation worst part
During solidification, which represents the transition of the average casting speed that best corresponds to
The period A and the coagulation period B are adopted.
The continuous casting method described.