JP2001138019A - Continuous casting method - Google Patents

Continuous casting method

Info

Publication number
JP2001138019A
JP2001138019A JP32608299A JP32608299A JP2001138019A JP 2001138019 A JP2001138019 A JP 2001138019A JP 32608299 A JP32608299 A JP 32608299A JP 32608299 A JP32608299 A JP 32608299A JP 2001138019 A JP2001138019 A JP 2001138019A
Authority
JP
Japan
Prior art keywords
slab
cooling
temperature
steel
casting
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
JP32608299A
Other languages
Japanese (ja)
Inventor
Yoshiki Ito
Toru Kato
義起 伊藤
徹 加藤
Original Assignee
Sumitomo Metal Ind Ltd
住友金属工業株式会社
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Sumitomo Metal Ind Ltd, 住友金属工業株式会社 filed Critical Sumitomo Metal Ind Ltd
Priority to JP32608299A priority Critical patent/JP2001138019A/en
Publication of JP2001138019A publication Critical patent/JP2001138019A/en
Pending legal-status Critical Current

Links

Abstract

PROBLEM TO BE SOLVED: To provide a continuous casting method of a low alloy steel cast slab, with which the development of transverse fracture and transverse crack developed at the straightening of the cast slab even in the case of changing the casting speed or the cast slab size. SOLUTION: When the cast slab having 1.8-10.5 ratio of the width to the thickness is cast, during the section from the starting of cooling just after the outlet of a mold to at least 1.5 m in the casting direction, the cast slab is cooled under condition, in which a value of the water spraying ratio Q (L/kg of steel) of secondary cooling defined with the following formula (A) becomes 0.4-0.75, and the surface temperature of the cast slab is made to not above the Ar3 transformation point and thereafter, returned back to >=850 deg.C to straighten the bending thereof. Q=W/(H×D×Vc×ρ)...(A). Wherein, W: the cooling water quantity (L/min) of the secondary cooling, H: the width (m) of the cast slab, D: the thickness (m) of the cast slab, Vc: the casting speed (m/min) and ρ: the density (kg/m3) of the molten steel.

Description

【発明の詳細な説明】DETAILED DESCRIPTION OF THE INVENTION
【0001】[0001]
【発明の属する技術分野】本発明は、良好な表面品質の
低合金鋼の鋳片を得ることができる鋼の連続鋳造方法に
関する。
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting method of steel capable of obtaining a low alloy steel slab of good surface quality.
【0002】[0002]
【従来の技術】近年、厚板製品などにおいて、機械的性
質上の要求から、Nb、V、Ni、Cuなどの合金元素
を含有させた低合金鋼が多く用いられている。これら低
合金鋼を湾曲型または垂直曲げ型の連続鋳造機を用いて
鋳造する場合に、鋳片表面に横割れ、横ひび割れと呼ば
れる割れが発生しやすい。鋳片が矯正される際に、鋳片
表面に働く応力が、これら低合金鋼に固有の限界応力を
超えるために、鋳片表面にこれらの割れが発生する。
2. Description of the Related Art In recent years, low-alloy steels containing alloy elements such as Nb, V, Ni, and Cu have been widely used in thick plate products and the like due to demands on mechanical properties. When these low alloy steels are cast using a curved or vertical bending type continuous casting machine, cracks called horizontal cracks and horizontal cracks are likely to occur on the slab surface. When the slab is straightened, the stress acting on the slab surface exceeds the limit stress inherent in these low alloy steels, so that these cracks occur on the slab surface.
【0003】Nb、V、Ni、Cuなどの合金元素を含
有する低合金鋼の鋳片に横ひび割れなどが発生しやすい
理由をさらに説明すると、次のとおりである。これら低
合金鋼の鋳片の熱間延性は、鋳片の凝固組織がγ相から
α相に変態するA3 変態点の温度近傍、すなわち、60
0〜850℃の温度領域で著しく低下する。さらに、こ
れら低合金鋼の鋳片では、鋳型から引き抜かれた後の二
次冷却過程で、AlNやNbCなどがγ粒界に析出しや
すい。AlNやNbCなどが析出したγ粒界は、応力が
作用すると割れやすい。したがって、600〜850℃
の温度領域でこれら低合金鋼の鋳片が矯正されると、脆
化温度域であることとγ粒界の析出物によって、鋳片表
面に横割れや横ひび割れが発生しやすい。
[0003] The reason why lateral cracks and the like are likely to occur in a low alloy steel slab containing alloying elements such as Nb, V, Ni and Cu will be further described as follows. The hot ductility of the cast slabs of these low alloy steels is close to the temperature of the A 3 transformation point at which the solidified structure of the cast slab is transformed from the γ phase to the α phase, ie, 60 ° C.
In the temperature range of 0 to 850 ° C., the temperature significantly decreases. Furthermore, in these low-alloy steel slabs, AlN, NbC, and the like are likely to precipitate at the γ grain boundary in the secondary cooling process after being drawn from the mold. Γ grain boundaries on which AlN, NbC, etc. are precipitated are liable to crack when stress is applied. Therefore, 600-850 ° C
When the slabs of these low alloy steels are corrected in the above temperature range, lateral cracks and lateral cracks are likely to occur on the surface of the slab due to the brittleness temperature range and precipitates at the γ grain boundary.
【0004】そこで、矯正時の鋳片表面温度を、600
〜850℃の熱間延性の低下する温度域(以下、脆化温
度域と記す)の低温側または高温側として、脆化温度域
を回避し、鋳片表面の横ひび割れなどの発生を防止する
方法が採られている。
Therefore, the slab surface temperature at the time of straightening is set to 600
As a low temperature side or a high temperature side of a temperature range in which hot ductility is reduced to 850 ° C. (hereinafter referred to as an embrittlement temperature range), avoid the embrittlement temperature range and prevent the occurrence of lateral cracks and the like on the slab surface. The method has been adopted.
【0005】特公昭58−3790号公報では、脆化温
度域が820〜950℃である鋼を鋳造する際に、2次
冷却により鋳片を強冷却して、鋳片の表面温度を650
〜700℃とし、その後矯正位置で鋳片の表面温度を7
00〜800℃として、脆化温度域を低温側に回避する
ことにより、横ひび割れなどを防止する方法が提案され
ている。
In Japanese Patent Publication No. 58-3790, when a steel having an embrittlement temperature range of 820 to 950 ° C. is cast, the slab is strongly cooled by secondary cooling to reduce the surface temperature of the slab to 650.
To 700 ° C, and then the surface temperature of the slab at the straightening position is 7
A method has been proposed in which the embrittlement temperature range is set to a low temperature side at a temperature of 00 to 800 ° C. to prevent lateral cracks and the like.
【0006】しかし、この方法では、Nb、V、Ni、
Cuなどの合金元素を含有する低合金鋼の場合に、いっ
たん鋳片表面温度を脆化温度域より低下させるために、
鋳片を強冷却する際に、鋳片表面に厚い酸化皮膜が発生
しやすい。これら酸化皮膜の厚さは、鋳片表面の位置に
より不均一になりやすく、酸化皮膜の厚い部分の鋳片表
面は、二次冷却時に冷却されにくくなる。したがって、
鋳片の表面温度が不均一になりやすい。そのため、部分
的に鋳片表面の温度が脆化温度域になる場合があり、矯
正時に、鋳片表面に横ひび割れなどが発生する場合があ
る。
However, in this method, Nb, V, Ni,
In the case of low alloy steel containing alloy elements such as Cu, in order to temporarily lower the slab surface temperature from the embrittlement temperature range,
When the slab is strongly cooled, a thick oxide film is easily generated on the slab surface. The thickness of these oxide films tends to be non-uniform depending on the position of the slab surface, and the slab surface of the thick portion of the oxide film is less likely to be cooled during secondary cooling. Therefore,
The surface temperature of the slab tends to be uneven. For this reason, the temperature of the slab surface may partially become the embrittlement temperature range, and horizontal crazing may occur on the slab surface during straightening.
【0007】一方、特開平9−47854号公報では、
鋳片を鋳型から引き抜いた後、1分以内に鋳片表面温度
をA3 変態点以下とし、その後復熱させ、矯正点におけ
る鋳片表面温度を850℃以上とする方法が提案されて
いる。
On the other hand, in Japanese Patent Application Laid-Open No. 9-47854,
After withdrawal of the slab from the mold, the cast slab surface temperature within 1 minute to less than A 3 transformation point causes then recuperation is, how to cast slab surface temperature 850 ° C. or higher in the straightening points is proposed.
【0008】しかし、この方法では、鋳片サイズが大き
かったり、または、鋳造速度が速い場合に、1分以内に
鋳片表面温度をA3 変態点以下とし、その後鋳片表面温
度を850℃以上に復熱させて鋳片を矯正しても、鋳片
表面に横ひび割れなどが発生する場合がある。
However, according to this method, when the slab size is large or the casting speed is high, the slab surface temperature is reduced to the A 3 transformation point or lower within one minute, and then the slab surface temperature is set to 850 ° C. or higher. Even if the slab is corrected by reheating to a temperature, lateral cracks or the like may occur on the slab surface.
【0009】また、特開平9−253814号公報で
は、上記特開平9−47854号公報と同様に、鋳型出
口の下方で鋳片を強冷却し、鋳片の表面温度を、いった
ん脆化温度域よりも低温側に低下させ、その後、脆化温
度域よりも高温側に復熱させて、鋳片の矯正時の横ひび
割れなどの発生を防止する方法が提案されている。鋳片
の表面温度をいったん低温にして、復熱させることによ
り、鋳片のミクロ組織を、γ粒界を不明瞭化させたフェ
ライトとパーライト組織とすることによって、横ひび割
れなどの発生を防止する方法である。
Further, in Japanese Patent Application Laid-Open No. 9-253814, similarly to the above-mentioned Japanese Patent Application Laid-Open No. 9-47854, the slab is strongly cooled below the outlet of the mold, and the surface temperature of the slab is temporarily reduced to the brittle temperature range. There has been proposed a method of lowering the temperature to a lower temperature side and then recovering the temperature to a higher temperature side than the embrittlement temperature range to prevent the occurrence of lateral cracks and the like when the slab is corrected. By reducing the surface temperature of the slab once and reheating it, the microstructure of the slab is changed to ferrite and pearlite structure in which the γ grain boundaries are obscured, thereby preventing the occurrence of lateral cracks and the like. Is the way.
【0010】しかし、この方法では、二次冷却条件が単
位時間当たり、鋳片表面の単位面積当たりの平均水量密
度(リットル/cm2 ・分)によって規定されているた
め、鋳造速度や、鋳片サイズが変化した場合に、適正な
冷却を行うことができなくなる場合がある。とくに、高
速の鋳造速度の場合や鋳片サイズが大きい場合に、冷却
水量が不足するため、γ粒界が不明瞭化せず、鋳片のミ
クロ組織を適正に制御できなくなる場合がある。そのた
め、鋳片表面に横ひび割れなどが発生しやすくなる。
However, in this method, since the secondary cooling condition is defined by the average water density (liter / cm 2 · min) per unit time per unit area of the slab surface, the casting speed and the slab When the size changes, proper cooling may not be performed in some cases. In particular, when the casting speed is high or the size of the slab is large, the amount of cooling water is insufficient, so that the γ grain boundary does not become unclear and the microstructure of the slab may not be properly controlled. Therefore, horizontal cracks and the like are likely to occur on the surface of the slab.
【0011】[0011]
【発明が解決しようとする課題】本発明は、鋳造速度や
鋳片サイズが変化しても、鋳片の曲がり矯正時に発生す
る横割れや横ひび割れなどの割れ(以下、鋳片表面割れ
と記す)を安定して防止できる低合金鋼の鋳片の連続鋳
造方法を提供することを目的とする。
DISCLOSURE OF THE INVENTION The present invention relates to cracks such as lateral cracks and lateral cracks that occur when straightening a slab, even if the casting speed or slab size changes (hereinafter referred to as slab surface cracks). It is an object of the present invention to provide a continuous casting method of a low alloy steel slab which can stably prevent the above.
【0012】[0012]
【課題を解決するための手段】本発明の要旨は、厚さに
対する幅の比が1.8〜10.5である鋳片の鋳造時、
鋳型出口直後から冷却を開始し鋳造方向に少なくとも
1.5mまでの間において、下記(A)式で定義される
二次冷却の比水量Q(リットル/kg−鋼)の値が0.
4〜0.75となる条件で鋳片を冷却して、鋳片表面温
度をA3 変態点以下とし、その後、復熱させて鋳片表面
温度を850℃以上とした状態で曲がりを矯正する鋼の
連続鋳造方法にある。
SUMMARY OF THE INVENTION The gist of the present invention is to provide a method for casting a slab having a width to thickness ratio of 1.8 to 10.5.
Cooling is started immediately after the mold outlet, and during a period of at least 1.5 m in the casting direction, the value of the specific water amount Q (liter / kg-steel) of the secondary cooling defined by the following equation (A) is 0.1.
By cooling the cast piece under the condition that the 4 to 0.75, the billet surface temperature not more than A 3 transformation point, then, to correct the bending in a state in which the cast slab surface temperature by recuperation 850 ° C. or higher In the continuous casting method of steel.
【0013】 Q=W/(H×D×Vc×ρ) ・・・(A) ここで、W:鋳片の二次冷却の冷却水量(リットル/
分) H:鋳片の幅(m) D:鋳片の厚さ(m) Vc:鋳造速度(m/分) ρ:溶鋼の密度(kg/m3 ) 上記(A)式における溶鋼の密度ρの値として7000
(kg/m3 )を用いればよい。
Q = W / (H × D × Vc × ρ) (A) where W: cooling water amount for secondary cooling of the slab (liter / liter)
Min) H: slab width (m) D: slab thickness (m) Vc: casting speed (m / min) ρ: density of molten steel (kg / m 3 ) density of molten steel in the above formula (A) 7000 as the value of ρ
(Kg / m 3 ).
【0014】本発明者らは、前述の本発明の課題を、下
記およびに示す対策によって解決した。
The present inventors have solved the above-mentioned problems of the present invention by the following measures.
【0015】本発明の方法では、鋳片表面の単位面積
当たりの平均水量密度(リットル/cm2 ・分)ではな
くて、前述の(A)式で定義する比水量Q(リットル/
kg−鋼)の値を適正条件として、鋳片を二次冷却す
る。したがって、鋳造速度や鋳片サイズが変化しても、
鋳片の二次冷却条件を適正に保持することができる。
In the method of the present invention, the specific water amount Q (liter / liter) defined by the above-mentioned equation (A) is used instead of the average water density (liter / cm 2 · minute) per unit area of the slab surface.
The slab is secondarily cooled with the value of (kg-steel) as an appropriate condition. Therefore, even if the casting speed or slab size changes,
The secondary cooling condition of the slab can be appropriately maintained.
【0016】鋳型出口直後から冷却を開始し鋳造方向
に少なくとも1.5mまでの間において、上記(A)式
で定義される二次冷却の比水量Q(リットル/kg−
鋼)の値が0.4〜0.75となる条件で鋳片を冷却し
て、鋳片表面温度をA3 変態点以下とし、その後、復熱
させて、鋳片表面温度850℃以上で鋳片の曲がりを矯
正する。
Cooling is started immediately after the mold outlet, and the specific water amount Q (liter / kg-
The slab is cooled under the condition that the value of (steel) is 0.4 to 0.75, the slab surface temperature is set to the A 3 transformation point or lower, and then reheated, and the slab surface temperature is set to 850 ° C. or higher. Straighten the slab.
【0017】上述のように鋳型出口直後で適正な条件で
鋳片を二次冷却し、鋳片表面温度をA3 変態点以下とす
ることにより、鋳片のミクロ組織を、γ粒界を不明瞭化
させたフェライトとパーライト組織とすることができ
る。また、γ粒が成長することを抑制できる。γ粒界が
不明瞭で小さなγ粒のγ粒界は、鋳片の矯正時に鋳片表
面割れが発生しにくい。
As described above, the slab is secondarily cooled under appropriate conditions immediately after the mold exit, and the slab surface temperature is set to the A 3 transformation point or lower, so that the slab microstructure and the γ grain boundary are not affected. A clarified ferrite and pearlite structure can be obtained. In addition, the growth of γ grains can be suppressed. The γ grain boundaries of small γ grains with unclear γ grain boundaries are less likely to cause slab surface cracks during slab correction.
【0018】γ粒界を不明瞭化させたフェライトとパー
ライト組織からなる鋳片のミクロ組織とは、高温側から
3 変態点より低温側に鋳片が冷却される際に、フェラ
イトがγ粒界に粒状に生成した状態のミクロ組織のこと
を意味する。γ粒界に粒状にフェライトが生成するため
に、γ粒界が不明瞭になる。このようなミクロ組織は、
上述するように、鋳型出口直後に適正な条件で鋳片を強
冷却することにより得られる。また、鋳型出口直後から
鋳片を強冷却するので、γ粒が大きく成長する時間がな
く、小さいγ粒が得られる。
The microstructure of a slab composed of ferrite and a pearlite structure in which the γ grain boundaries are obscured means that when the slab is cooled from a high temperature side to a lower temperature side from the A 3 transformation point, the γ grain It means a microstructure in a state formed in a grain boundary. Since ferrite is generated in a granular form at the γ grain boundary, the γ grain boundary becomes unclear. Such a microstructure is
As described above, it is obtained by strongly cooling the slab under appropriate conditions immediately after the exit of the mold. Also, since the slab is strongly cooled immediately after the mold exit, there is no time for the γ grains to grow large, and small γ grains can be obtained.
【0019】逆に、鋳型出口直後の鋳片を弱く二次冷却
すると、γ粒界が明瞭となる。このγ粒界が明瞭なミク
ロ組織とは、γ粒界にフェライトがフィルム状に生成し
たミクロ組織である。
Conversely, when the slab immediately after the exit of the mold is weakly secondary cooled, the γ grain boundary becomes clear. The microstructure in which the γ grain boundary is clear is a microstructure in which ferrite is formed in a film shape at the γ grain boundary.
【0020】さらに、鋳片の曲がり矯正時の鋳片表面温
度を、脆化温度域よりも高温側の850℃以上とするの
で、Nb、V、Ni、Cuなどの合金元素を含有する低
合金鋼の場合でも、鋳片表面割れの発生を防止できる。
低合金鋼の脆化温度は、前述のように600〜850℃
の温度領域である。
Further, since the slab surface temperature at the time of straightening the slab is set to 850 ° C. or higher, which is higher than the embrittlement temperature range, a low alloy containing alloy elements such as Nb, V, Ni, and Cu is used. Even in the case of steel, the occurrence of surface slab cracks can be prevented.
The embrittlement temperature of low alloy steel is 600 to 850 ° C as described above.
Temperature range.
【0021】なお、鋳片の表面温度とは、たとえば、放
射温度計により測定することのできる表面温度であり、
鋳片の表面から表皮直下までの温度を意味する。また、
この鋳片の表面温度は、凝固伝熱解析による計算によっ
ても求めることができる。すなわち、鋼の種類、鋳片の
サイズ、鋳造速度、鋳片の二次冷却条件などの条件が決
まれば、溶鋼メニスカスからの距離に応じた鋳片の表面
温度を計算で求めることができる。また、表面熱伝達係
数を適切に選択することにより、この計算で求めた鋳片
の表面温度は実測の表面温度とよく一致させることがで
きる。
The surface temperature of the slab is, for example, a surface temperature that can be measured by a radiation thermometer.
It means the temperature from the surface of the slab to just below the skin. Also,
The surface temperature of the slab can also be obtained by calculation by solidification heat transfer analysis. That is, if conditions such as the type of steel, the size of the slab, the casting speed, and the secondary cooling condition of the slab are determined, the surface temperature of the slab according to the distance from the molten steel meniscus can be calculated. Further, by appropriately selecting the surface heat transfer coefficient, the surface temperature of the slab obtained by this calculation can be made to match well with the actually measured surface temperature.
【0022】[0022]
【発明の実施の形態】図1は、本発明の方法を実施する
場合の連続鋳造装置の例を模式的に示す図である。鋳型
1から引き抜かれた直後の鋳片2は、ガイドロール対3
で支持、案内され、ミストスプレーノズル4などにより
水が噴霧され、二次冷却される。その後、鋳片はピンチ
ロール5により引き抜かれるとともに、矯正点の位置に
あるピンチロール6で鋳片の曲がりが矯正される。
FIG. 1 is a view schematically showing an example of a continuous casting apparatus when the method of the present invention is carried out. The slab 2 immediately after being pulled out of the mold 1 has a guide roll pair 3
, Sprayed with water by a mist spray nozzle 4 or the like, and secondary cooled. Thereafter, the slab is pulled out by the pinch roll 5, and the slab is bent by the pinch roll 6 at the position of the correction point.
【0023】本発明が対象とする鋳片は、厚さに対する
幅の比が1.8〜10.5の範囲の鋳片である。
The slab to which the present invention is directed is a slab having a width to thickness ratio in the range of 1.8 to 10.5.
【0024】厚さに対する幅の比が1.8未満のブルー
ムまたはビレットの鋳片、または、厚さに対する幅の比
が10.5を超える扁平比の大きいスラブ鋳片では、鋳
片表面に横割れや横ひび割れなどが発生しにくいので対
象外とする。
In the case of bloom or billet slab having a width to thickness ratio of less than 1.8 or a slab slab having a large aspect ratio having a width to thickness ratio of more than 10.5, the slab surface has a width Since it is difficult for cracks and lateral cracks to occur, it is excluded from the target.
【0025】本発明の方法では、鋳型出口直後から鋳片
の冷却を開始し、鋳造方向に少なくとも1.5mまでの
間において、鋳片の二次冷却の比水量を適正な条件の範
囲に調整する。
In the method of the present invention, the cooling of the slab is started immediately after the mold exit, and the specific water amount of the secondary cooling of the slab is adjusted to an appropriate range within at least 1.5 m in the casting direction. I do.
【0026】鋳型出口直後から鋳造方向に少なくとも
1.5mまでの間の鋳片の厚さ中心部には、未凝固部が
多く存在する。このような鋳片を適正な二次冷却の比水
量の条件で冷却することにより、既に凝固した凝固殻で
ある鋳片の表面温度を、いったんA3 変態点よりも低下
させることができる。鋳型出口から鋳造方向に少なくと
も1.5mまでの位置において、鋳片の二次冷却を終了
させるので、その後、鋳片表面温度を850℃以上に復
熱させることができる。また、このような二次冷却によ
って、γ粒界が不明瞭で、かつ、小さなγ粒とすること
ができるのは前述のとおりである。
There are many unsolidified portions in the center of the thickness of the slab between immediately after the mold exit and at least 1.5 m in the casting direction. By cooling such a slab under the conditions of a ratio water proper secondary cooling, the surface temperature of the slab is already solidified solidified shell can be lowered than once A 3 transformation point. Since the secondary cooling of the slab is terminated at a position at least 1.5 m from the mold outlet in the casting direction, the slab surface temperature can be returned to 850 ° C. or higher thereafter. As described above, by such secondary cooling, the γ grain boundaries are unclear and small γ grains can be obtained.
【0027】鋳片の二次冷却の終了位置は、鋳型出口か
ら鋳造方向に0.7〜1.3mの間とするのが望まし
い。
It is desirable that the end position of the secondary cooling of the slab is between 0.7 and 1.3 m in the casting direction from the mold outlet.
【0028】0.7m未満までの領域において、鋳片の
二次冷却を終了するには、ミストスプレーノズル1個当
たりの冷却水量が多くなり、ミストスプレーノズルおよ
び冷却水用配管が大きくなり、設備費が高くなる。ま
た、1.3mを超える領域まで二次冷却する場合は、エ
アーミストノズルの配置個数が多くなり、設備費が高く
なる。
In order to complete the secondary cooling of the slab in the area of less than 0.7 m, the amount of cooling water per mist spray nozzle increases, the mist spray nozzle and the piping for cooling water increase, Costs will be higher. In the case of secondary cooling to a region exceeding 1.3 m, the number of arranged air mist nozzles increases, and the equipment cost increases.
【0029】本発明の方法では、前述の(A)式で定義
する二次冷却の比水量Q(リットル/kg−鋼)が0.
4〜0.75となる条件で鋳造する。
In the method of the present invention, the specific water amount Q (liter / kg-steel) of the secondary cooling defined by the above equation (A) is 0.1.
Casting is performed under the conditions of 4 to 0.75.
【0030】比水量Q(リットル/kg−鋼)が0.4
未満では、鋳片の二次冷却が不十分となり、鋳片の表面
温度をいったんA3 変態点以下まで冷却することが困難
となる。いったんA3 変態点以下まで鋳片表面温度を低
下できないと、鋳片のミクロ組織において、γ粒界を不
明瞭化できず、また、小さなγ粒を得ることができない
ので、鋳片表面割れが発生しやすくなる。また、比水量
が0.75を超える場合には、鋳片が過冷却されるた
め、復熱時に850℃以上に復熱させることが困難とな
る。そのため、鋳片の矯正時に鋳片の表面温度が脆化温
度域となり、鋳片表面割れが発生しやすくなる。
The specific water quantity Q (liter / kg-steel) is 0.4
In the secondary cooling of the slab becomes insufficient, once it is difficult to cool to below A 3 transformation point and the surface temperature of the slab below. Once can not reduce the cast slab surface temperature to below the A 3 transformation point, the microstructure of the slab can not obscure the γ grain boundary, and since it is impossible to obtain a small γ grains, the cast slab surface cracks More likely to occur. Further, when the specific water amount exceeds 0.75, the slab is supercooled, so that it becomes difficult to recover the temperature to 850 ° C. or more at the time of reheating. Therefore, when the slab is straightened, the surface temperature of the slab becomes the embrittlement temperature range, and the slab surface cracks easily occur.
【0031】図2は、鋳片表面割れに及ぼす鋳片の二次
冷却の比水量Q(リットル/kg−鋼)と鋳造速度Vc
(m/分)との関係を示す図である。
FIG. 2 shows the specific water amount Q (liter / kg-steel) of the secondary cooling of the slab which affects the slab surface cracking and the casting speed Vc.
It is a figure which shows the relationship with (m / min).
【0032】垂直部の長さが3.0mである垂直曲げ型
連続鋳造機を用いて、C含有率0.10〜0.15質量
%、Nb含有率0.015質量%である中炭素低合金鋼
を鋳造した。鋳型出口直後から冷却を開始し、鋳造方向
に1.5mまでの間において鋳片を二次冷却し、このと
き、鋳片の二次冷却の比水量Qおよび鋳造速度Vcを変
化させて試験した。なお、この二次冷却を行う領域より
下流側の位置にある鋳片については、二次冷却を実施し
ていない。
Using a vertical bending type continuous casting machine having a vertical part length of 3.0 m, a medium carbon low content having a C content of 0.10 to 0.15 mass% and an Nb content of 0.015 mass%. Alloy steel was cast. Cooling was started immediately after the mold exit, and the slab was secondarily cooled to 1.5 m in the casting direction. At this time, the test was performed while changing the specific water amount Q and the casting speed Vc of the secondary cooling of the slab. . In addition, the secondary cooling is not performed for the slab located downstream from the region where the secondary cooling is performed.
【0033】図2中に符号(a)で示す曲線は、断面形
状が矩形で、厚さ300mm、幅650mmで、厚さに
対する幅の比が2.2である鋳片を、二次冷却時の冷却
水量を500リットル/分の条件で冷却し、鋳造速度を
変更した試験の結果を示す曲線である。同じく、符号
(b)で示す曲線は、厚さ200mm、幅1000m
m、厚さに対する幅の比が5.0である鋳片を、二次冷
却時の冷却水量を1500リットル/分の条件で冷却
し、鋳造速度を変更した試験の結果を、また、符号
(c)で示す曲線は、厚さ230mm、幅2300m
m、厚さに対する幅の比が10.0である鋳片を、二次
冷却時の冷却水量を2300リットル/分の条件で冷却
し、鋳造速度を変更した試験の結果を、それぞれ示す曲
線である。
The curve indicated by reference numeral (a) in FIG. 2 shows a slab having a rectangular cross section, a thickness of 300 mm, a width of 650 mm, and a width to thickness ratio of 2.2. 5 is a curve showing the results of a test in which the cooling water amount was cooled under the condition of 500 liters / minute and the casting speed was changed. Similarly, the curve shown by the symbol (b) is a thickness of 200 mm and a width of 1000 m.
m, the slab having a width-to-thickness ratio of 5.0 was cooled under the condition that the cooling water volume at the time of the secondary cooling was 1500 liters / minute, and the result of the test in which the casting speed was changed was represented by a code ( The curve shown in c) has a thickness of 230 mm and a width of 2300 m
m, the slab having a width-to-thickness ratio of 10.0 was cooled under the condition that the cooling water amount at the time of secondary cooling was 2300 liters / minute, and the results of tests in which the casting speed was changed were shown by curves respectively. is there.
【0034】図2から、少なくとも鋳造速度または鋳片
サイズが変化しても、鋳型出口直後から冷却を開始し、
鋳造方向に1.5mまでの間の鋳片の二次冷却の比水量
Qを0.4〜0.75(リットル/kg−鋼)とするこ
とにより、鋳片表面割れの発生を防止できることが分か
る。
From FIG. 2, even if at least the casting speed or the slab size changes, cooling is started immediately after the mold exit,
By setting the specific water amount Q of the secondary cooling of the slab to 1.5 m in the casting direction to 0.4 to 0.75 (liter / kg-steel), it is possible to prevent the occurrence of a slab surface crack. I understand.
【0035】[0035]
【実施例】図1に示す装置構成で、垂直部の長さが3.
0mである垂直曲げ型連続鋳造機を用いて、鋳片サイ
ズ、鋳造速度および二次冷却の比水量Qの条件を変化さ
せて試験した。鋳片を二次冷却する領域は、本発明の方
法で規定する条件の範囲内の鋳型出口直後から冷却を開
始し、鋳造方向に0.8mまでの間の領域とした。な
お、この二次冷却する領域より下流側の位置にある鋳片
については、鋳片の二次冷却を行わなかった。表1に、
用いた中炭素低合金鋼の化学組成を示す。Nb、Cu、
Niを含む低合金鋼である。この鋼のA3 変態点は86
5℃であり、また、脆化温度域は710〜840℃であ
る。
DESCRIPTION OF THE PREFERRED EMBODIMENTS In the apparatus configuration shown in FIG.
Using a vertical bending type continuous casting machine of 0 m, the test was performed while changing the conditions of the slab size, the casting speed, and the specific water amount Q of the secondary cooling. The region for secondary cooling of the slab was cooled immediately after exiting the mold within the range defined by the method of the present invention, and was set to a region up to 0.8 m in the casting direction. The slab at a position downstream of the secondary cooling area was not subjected to the secondary cooling of the slab. In Table 1,
The chemical composition of the medium carbon low alloy steel used is shown. Nb, Cu,
It is a low alloy steel containing Ni. The A 3 transformation point of this steel is 86
5 ° C., and the embrittlement temperature range is 710 to 840 ° C.
【0036】[0036]
【表1】 [Table 1]
【0037】鋳片サイズは、本発明の方法で規定する厚
さに対する幅の比の条件の範囲内のサイズとし、次の3
種類で試験した。厚さ300mm、幅650mm、厚さ
に対する幅の比が2.2である鋳片、厚さ200mm、
幅1000mm、厚さに対する幅の比が5.0である鋳
片、厚さ230mm、幅2300mm、厚さに対する幅
の比が10.0である鋳片の3種類とした。
The slab size is a size within the range of the ratio of the width to the thickness specified by the method of the present invention.
Tested by type. A slab having a thickness of 300 mm, a width of 650 mm, and a width to thickness ratio of 2.2, a thickness of 200 mm,
There were three types of slabs, a slab having a width of 1000 mm and a width to thickness of 5.0, and a slab having a thickness of 230 mm, a width of 2300 mm and a width to thickness of 10.0.
【0038】各試験では、それぞれ3ヒートの連々鋳を
行い、鋳造中に放射温度計により、二次冷却直後の鋳片
表面温度および矯正位置での鋳片の表面温度を測定し
た。また、各試験では、各ヒートから鋳造方向の長さ1
mの鋳片サンプルを採取し、鋳片表面割れを観察しやす
いように、鋳片サンプルの表面をスカーフィングして鋳
片表層部の酸化物を取り除いた後、ダイチェック(染色
浸透探傷試験)を行って、鋳片表面割れの発生の状況を
目視で観察した。鋳片表面割れの発生の程度の評価A
は、発生なし、評価Bは、その鋳片を素材として熱間圧
延する前には、鋳片表面の手入れが必要な程度の鋳片表
面割れが発生しているもの、評価Cは著しい鋳片表面割
れが発生しているものである。
In each test, three heats were cast continuously, and the surface temperature of the slab immediately after the secondary cooling and the surface temperature of the slab at the straightening position were measured by a radiation thermometer during the casting. In each test, the length in the casting direction from each heat was 1 mm.
A slab sample of m is collected, and the surface of the slab sample is scarfed to remove oxides on the surface layer of the slab so that cracks on the slab surface can be easily observed. , And the state of occurrence of surface slab cracks was visually observed. Evaluation of degree of occurrence of slab surface cracking A
Means that no slab is generated, and evaluation B is that a slab surface crack is generated to the extent that the slab surface requires maintenance before hot rolling using the slab as a raw material. Surface cracks have occurred.
【0039】また、鋳片サンプルから光学顕微鏡観察用
サンプルを切り出して研磨し、5%ナイタール腐食を行
った後、光学顕微鏡により、γ粒界におけるフェライト
の生成状況を観察した。表2に各試験条件と各試験結果
を示す。
Further, a sample for observation with an optical microscope was cut out from the slab sample, polished and subjected to 5% nital corrosion, and the state of formation of ferrite at the γ grain boundary was observed with an optical microscope. Table 2 shows each test condition and each test result.
【0040】[0040]
【表2】 [Table 2]
【0041】本発明例の試験No.1〜No.5では、
本発明の方法で規定する厚さに対する幅の比の条件の範
囲内で、3種類のサイズの鋳片について、本発明の方法
で規定する鋳片の二次冷却の比水量Qの条件の範囲内で
試験した。
Test No. of the present invention example 1 to No. In 5,
Within the range of the condition of the ratio of the width to the thickness specified by the method of the present invention, the range of the condition of the specific water amount Q of the secondary cooling of the slab specified by the method of the present invention for three types of slabs Tested within.
【0042】これら試験No.1〜No.5では、鋳片
の二次冷却により、二次冷却直後の鋳片の表面温度をい
ったんA3 変態点以下の720〜800℃とした。その
後、復熱させ、この鋼の脆化温度域の高温側である鋳片
表面温度880℃〜950℃で鋳片を矯正した。そのた
めに、鋳片表層部のミクロ組織は、γ粒界には、粒状に
フェライトが生成して、γ粒界が不明瞭になっており、
鋳片表面割れ発生の評価はAで、横ひび割れなどの鋳片
表面割れは発生しなかった。
In these test nos. 1 to No. In No. 5, the surface temperature of the slab immediately after the secondary cooling was temporarily set to 720 to 800 ° C. below the A 3 transformation point by the secondary cooling of the slab. Thereafter, the steel was reheated, and the slab was straightened at a slab surface temperature of 880 ° C. to 950 ° C., which is a high temperature side of the brittle temperature range of the steel. Therefore, the microstructure of the surface layer of the slab, ferrite is generated in a granular manner at the γ grain boundary, and the γ grain boundary is unclear,
The evaluation of the slab surface crack generation was A, and no slab surface cracks such as lateral cracks were generated.
【0043】比較例の試験No.6〜No.8では、本
発明の方法で規定する厚さに対する幅の比の条件の範囲
内で、3種類のサイズの鋳片について、本発明の方法で
規定する鋳片の二次冷却の比水量Qの条件を外して試験
した。
Test No. of Comparative Example 6-No. 8, within the range of the condition of the ratio of the width to the thickness specified by the method of the present invention, for the slabs of three kinds of sizes, the specific water amount Q of the secondary cooling of the slab specified by the method of the present invention. The test was performed with the conditions removed.
【0044】試験No.6では、鋳片の二次冷却の比水
量Qを、本発明の方法で規定する条件の上限を超えた
1.05リットル/kg−鋼とした。鋳片表面割れ発生
の評価はCであり、著しい鋳片表面割れが発生した。鋳
片表層部のミクロ組織において、γ粒界には、粒状にフ
ェライトが生成して、γ粒界は不明瞭であった。ただ
し、鋳片が過冷却されたため、いったんA3 変態点以下
の670℃となった鋳片の表面温度を、A3 変態点を超
える温度に復熱させることができなかった。そのため、
矯正時の鋳片の表面温度はこの鋼の脆化温度域である8
20℃となり、鋳片の矯正時、著しい鋳片表面割れが発
生した。
Test No. In No. 6, the specific water amount Q in the secondary cooling of the slab was set to 1.05 liter / kg-steel, which exceeded the upper limit of the condition specified by the method of the present invention. The evaluation of the occurrence of slab surface cracking was C, and significant slab surface cracking occurred. In the microstructure of the surface layer of the slab, ferrite was generated in a granular form at the γ grain boundary, and the γ grain boundary was unclear. However, because the slab is supercooled, once the surface temperature of the slab to obtain the following 670 ° C. A 3 transformation point, could not be recuperation to a temperature above the A 3 transformation point. for that reason,
The surface temperature of the slab at the time of straightening is the brittle temperature range of this steel.
The temperature was 20 ° C., and when the slab was corrected, significant slab surface cracks occurred.
【0045】試験No.7およびNo.8では、鋳片の
二次冷却の比水量Qを、本発明の方法で規定する条件の
下限未満である0.35または0.29リットル/kg
−鋼とした。いずれも、鋳片表面割れ発生の評価はBで
あり、手入れの必要な程度の鋳片表面割れが発生した。
矯正時の鋳片の表面温度は890〜970℃であり、そ
の鋼の脆化温度域を高温側に回避されているものの、鋳
片の二次冷却が不十分となり、鋳片の表面温度をいった
んA3 変態点以下まで冷却することができなかった。そ
のため、鋳片表層部のミクロ組織において、γ粒界に
は、フェライトがフィルム状に生成し、γ粒界が明瞭と
なった。そのため、鋳片の矯正時、鋳片表面割れが発生
しやすくなった。
Test No. 7 and No. 7 In No. 8, the specific water amount Q of the secondary cooling of the slab is set to 0.35 or 0.29 liter / kg which is less than the lower limit of the condition specified by the method of the present invention.
-Steel. In each case, the evaluation of the occurrence of slab surface cracking was B, indicating that slab surface cracking required maintenance was generated.
The surface temperature of the cast slab at the time of straightening is 890 to 970 ° C., and although the brittle temperature range of the steel is avoided on the high temperature side, the secondary cooling of the cast slab is insufficient and the surface temperature of the cast slab is reduced. once it could not be cooled to below a 3 transformation point. Therefore, in the microstructure of the surface layer of the slab, ferrite was formed in a film shape at the γ grain boundary, and the γ grain boundary became clear. Therefore, when the slab is corrected, the slab surface cracks are easily generated.
【0046】[0046]
【発明の効果】本発明の方法の適用により、鋳造速度や
鋳片サイズが変化しても、鋳片表面の横割れや横ひび割
れの発生を防止でき、表面品質の良好な低合金鋼の鋳片
を得ることができる。
According to the method of the present invention, even if the casting speed or the slab size changes, the occurrence of lateral cracks or lateral cracks on the slab surface can be prevented, and the casting of low alloy steel with good surface quality can be prevented. You can get a piece.
【図面の簡単な説明】[Brief description of the drawings]
【図1】本発明の方法を実施する場合の連続鋳造装置の
例を模式的に示す図である。
FIG. 1 is a diagram schematically illustrating an example of a continuous casting apparatus when a method of the present invention is performed.
【図2】鋳片表面割れに及ぼす鋳片の二次冷却の比水量
Qと鋳造速度Vcとの関係を示す図である。
FIG. 2 is a diagram showing a relationship between a specific water amount Q of secondary cooling of a slab and a casting speed Vc, which affect a slab surface crack.
【符号の説明】[Explanation of symbols]
1:鋳型 2:鋳片 3:ガイ
ドロール対 4:ミストスプレーノズル 5:ピン
チロール 6:矯正点の位置にあるピンチロール
1: mold 2: cast slab 3: guide roll pair 4: mist spray nozzle 5: pinch roll 6: pinch roll at the position of the correction point

Claims (1)

    【特許請求の範囲】[Claims]
  1. 【請求項1】厚さに対する幅の比が1.8〜10.5で
    ある鋳片の鋳造時、鋳型出口直後から冷却を開始し鋳造
    方向に少なくとも1.5mまでの間において、下記
    (A)式で定義される二次冷却の比水量Q(リットル/
    kg−鋼)の値が0.4〜0.75となる条件で鋳片を
    冷却して、鋳片表面温度をA3 変態点以下とし、その
    後、復熱させて鋳片表面温度を850℃以上とした状態
    で曲がりを矯正することを特徴とする鋼の連続鋳造方
    法。 Q=W/(H×D×Vc×ρ) ・・・(A) ここで、W:鋳片の二次冷却の冷却水量(リットル/
    分) H:鋳片の幅(m) D:鋳片の厚さ(m) Vc:鋳造速度(m/分) ρ:溶鋼の密度(kg/m3
    (1) When casting a slab having a width to thickness ratio of 1.8 to 10.5, cooling is started immediately after the mold exit and the following (A) ) The secondary cooling specific water volume Q (liter /
    (kg-steel), the slab is cooled under the condition that the value of the slab is 0.4 to 0.75, the slab surface temperature is set to the A 3 transformation point or lower, and then the slab is reheated to set the slab surface temperature to 850 ° C. A continuous casting method for steel, wherein the bending is corrected in the above state. Q = W / (H × D × Vc × ρ) (A) where W: cooling water amount for secondary cooling of the slab (liter / liter)
    Min) H: slab width (m) D: slab thickness (m) Vc: casting speed (m / min) ρ: density of molten steel (kg / m 3 )
JP32608299A 1999-11-16 1999-11-16 Continuous casting method Pending JP2001138019A (en)

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Publication Number Publication Date
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Country Link
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Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2007222920A (en) * 2006-02-24 2007-09-06 Jfe Steel Kk Method and apparatus for cooling continuous cast slab
JP2009000705A (en) * 2007-06-20 2009-01-08 Sumitomo Metal Ind Ltd Method for continuously casting cast slab
CN101983800A (en) * 2010-11-17 2011-03-09 中冶南方工程技术有限公司 Secondary cooling water distribution advanced control method for billet continuous casting machine
CN102059333A (en) * 2010-11-17 2011-05-18 中冶南方工程技术有限公司 Advanced secondary cooling water control system of billet continuous casting machine
CN102601333A (en) * 2011-12-09 2012-07-25 秦皇岛首秦金属材料有限公司 Method for controlling bulging of narrow surface of extra-thick plate blank with thickness of 400mm
CN102861890A (en) * 2012-09-19 2013-01-09 中冶南方工程技术有限公司 Secondary cooling method for reducing transverse cracks of corners of microalloy sheet billet
US8939194B2 (en) 2008-07-15 2015-01-27 Nippon Steel & Sumitomo Metal Corporation Continuous cast slab and producing method therefor
JP2016041436A (en) * 2014-08-18 2016-03-31 新日鐵住金株式会社 CONTINUOUS CASTING METHOD FOR Ni-CONTAINING STEEL
JP2017018961A (en) * 2015-07-07 2017-01-26 新日鐵住金株式会社 CONTINUOUS CASTING METHOD FOR STEEL CONTAINING Ni

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2007222920A (en) * 2006-02-24 2007-09-06 Jfe Steel Kk Method and apparatus for cooling continuous cast slab
JP4635902B2 (en) * 2006-02-24 2011-02-23 Jfeスチール株式会社 Continuous cast slab cooling method and continuous cast slab cooling device
JP2009000705A (en) * 2007-06-20 2009-01-08 Sumitomo Metal Ind Ltd Method for continuously casting cast slab
JP4600436B2 (en) * 2007-06-20 2010-12-15 住友金属工業株式会社 Continuous casting method for slabs
US8939194B2 (en) 2008-07-15 2015-01-27 Nippon Steel & Sumitomo Metal Corporation Continuous cast slab and producing method therefor
CN101983800A (en) * 2010-11-17 2011-03-09 中冶南方工程技术有限公司 Secondary cooling water distribution advanced control method for billet continuous casting machine
CN102059333A (en) * 2010-11-17 2011-05-18 中冶南方工程技术有限公司 Advanced secondary cooling water control system of billet continuous casting machine
CN101983800B (en) * 2010-11-17 2012-09-05 中冶南方工程技术有限公司 Secondary cooling water distribution advanced control method for billet continuous casting machine
CN102601333A (en) * 2011-12-09 2012-07-25 秦皇岛首秦金属材料有限公司 Method for controlling bulging of narrow surface of extra-thick plate blank with thickness of 400mm
CN102861890A (en) * 2012-09-19 2013-01-09 中冶南方工程技术有限公司 Secondary cooling method for reducing transverse cracks of corners of microalloy sheet billet
JP2016041436A (en) * 2014-08-18 2016-03-31 新日鐵住金株式会社 CONTINUOUS CASTING METHOD FOR Ni-CONTAINING STEEL
JP2017018961A (en) * 2015-07-07 2017-01-26 新日鐵住金株式会社 CONTINUOUS CASTING METHOD FOR STEEL CONTAINING Ni

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