JP4276419B2 - Powder for continuous casting of steel - Google Patents
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【０００１】
【発明の属する技術分野】
本発明は、鋼の連続鋳造において鋳型内に添加する鋼の連続鋳造用パウダーに関するものである。
【０００２】
【従来の技術】
鋼の連続鋳造においては、鋳型内に注入された溶鋼表面上に連続鋳造用パウダーを添加する。連続鋳造用パウダーはモールドパウダー、あるいは単にパウダーとも呼ばれ、高温の溶鋼に加熱されて溶融し、鋳型と凝固シェルの間に流入する。パウダーは主として、鋳型内溶鋼表面の保温および酸化防止、溶鋼中から浮上した非金属介在物の吸収、鋳型と凝固シェル間に流入するスラグフィルムによる潤滑作用、このフィルムによる鋳片よりの抜熱の制御を行うことを目的とする。これによって、優れた表面性状の鋳片を得るとともに、溶融したパウダーが溶鋼中に巻き込まれにくく、正常で良好な鋳片を製造する。
【０００３】
ところで、連続鋳造操業時には、操業条件の如何又はその変化による局所的な湯面変動に起因し、あるいは鋳型内に注入された溶鋼の注入流がメニスカス近傍で溶融したパウダーと溶鋼との界面を乱し、パウダーを溶鋼中に巻き込み、凝固シェルヘ付着したりする場合がある。特に高速連続鋳造においては注入流の流速が大きくなるので、パウダーを巻き込みやすくなる。巻き込まれたパウダーが鋳片に付着したままの状態で圧延を行うと、伸展されて冷延鋼板の表面欠陥の原因となるため、連続鋳造用パウダーには、鋳造中にパウダー巻き込みを起こさない性質を有することが要請される。
【０００４】
高粘性のパウダーを用いることにより、鋳型内溶鋼流動によるパウダーの巻き込みを防止することができ、パウダー巻き込みに起因する欠陥発生が低減されることが知られている。特に炭素濃度が０．０１質量％以下であるＩＦ鋼（Interstitial Free鋼）は、パウダー巻き込みに起因する鋳片及び冷延鋼板の表面欠陥が発生しやすい。極低炭素鋼は鋳造時の溶鋼表面付近に生成する凝固シェル先端の爪が長くなりやすく、この爪が原因でパウダー巻き込みが発生しやすいと考えられる。
【０００５】
特許文献１においては、極低炭素鋼用のモールドパウダーとして、１３００℃におけるパウダーの粘度を３ｐｏｉｓｅ以上とすることで、高速鋳造においてもモールドパウダーの巻き込みを低減できる点が記載されている。
【０００６】
【特許文献１】
特開平１０−２６３７６７号公報
【０００７】
【発明が解決しようとする課題】
極低炭素鋼用のモールドパウダーに粘度３ｐｏｉｓｅ以上の高粘性パウダーを使用することにより、溶鋼中へのモールドパウダーの巻き込みの頻度を減らすことは可能になった。ただし、鋳片へのパウダー巻き込みが皆無になるわけではない。モールドパウダーの粘度を上げた結果として、一部残存する巻き込みパウダーが、この鋳片を用いて製造した鋼板をプレス成形するに際し、プレス割れの原因となり易くなるという現象が発生することとなった。
【０００８】
本発明は、極低炭素鋼の連続鋳造において、パウダー巻き込みを防止しつつ、一部巻き込まれたパウダーがプレス割れの原因とならないような鋼の連続鋳造用パウダーを提供することを目的とする。
【０００９】
【課題を解決するための手段】
即ち、本発明の要旨とするところは以下の通りである。
（１）ＣａＯ／ＳｉＯ2が１．１１〜１．２の範囲であり、ＺｒＯ2：１〜７質量％、Ａｌ 2 Ｏ 3 ：２〜１０質量％を含有し、１３００℃における粘度が３．５〜１０ｐｏｉｓｅであり、Ａｌ含有量０．０１〜０．０６質量％の極低炭Ａｌキルド鋼の連続鋳造に用いることを特徴とする鋼の連続鋳造用パウダー。
（２）さらにＢ2Ｏ3：１〜７質量％を含有することを特徴とする上記（１）に記載の鋼の連続鋳造用パウダー。
【００１０】
【発明の実施の形態】
極低炭Ａｌキルド鋼の連続鋳造において、溶融金属中に巻き込まれたパウダーは、その成分中のＳｉＯ2が溶鋼中のＡｌによって還元され、かわりにＡｌ2Ｏ3が生成し、パウダーはＣａＯ−Ａｌ2Ｏ3の２元系介在物となる。ＣａＯ−Ａｌ2Ｏ3２元系介在物中のＣａＯ：Ａｌ2Ｏ3比と介在物の融点との関係についてみると、ＣａＯ：Ａｌ2Ｏ3比が１．１近傍で介在物の融点が最も低くなる。
【００１１】
従来、モールドパウダーの粘度を上げ、１３００℃における粘度を３ｐｏｉｓｅ以上にするためには、パウダー成分における塩基度（ＣａＯ／ＳｉＯ2）を０．８程度の低塩基度とすることによって実現していた。低塩基度でＳｉＯ2含有量が多いパウダーが溶鋼中に巻き込まれると、Ａｌによって還元されＡｌ2Ｏ3となるべきＳｉＯ2が多いので、Ａｌ2Ｏ3含有量が多く、ＣａＯ：Ａｌ2Ｏ3比が１．１よりも低いＣａＯ−Ａｌ2Ｏ3系介在物となる。このような組成の介在物は融点が高く、その後の圧延段階において介在物が破砕されにくい性質を有する。従来、高粘性パウダーを用いることによってパウダー巻き込みが減少するものの皆無とはならず、パウダー巻き込み起因介在物がプレス割れの原因となっていたのは、以上のように残存したパウダーの融点が高いのが原因であった。
【００１２】
一方、パウダーの１３００℃粘度を３ｐｏｉｓｅ以上に確保しつつパウダーの塩基度を上げることができれば、パウダー中のＳｉＯ2含有量が減少し、Ａｌで還元された後の介在物中のＣａＯ：Ａｌ2Ｏ3比が増加し、最も融点の低いＣａＯ：Ａｌ2Ｏ3＝１．１近傍の値を実現することが可能になる。
【００１３】
脱酸生成物としてのアルミナの浮上によってもパウダー中のＡｌ2Ｏ3は増加するが、増加代は無視できるほど小さく、同様に溶鋼中でのアルミナ系介在物とパウダー系介在物の合体によるパウダー系介在物中のＡｌ2Ｏ3増加も非常に小さい。
【００１４】
本発明は、以上の知見に基づいてなされたものであり、１３００℃における粘度が３〜１０ｐｏｉｓｅとしつつ、塩基度（ＣａＯ／ＳｉＯ2）を１．１〜１．２の範囲とすることにより、極低炭素鋼の連続鋳造においてパウダーの巻き込みを減少し、たとえ溶鋼中に巻き込まれても融点の低い介在物を生成し、プレス割れの少ない良好な品質の鋳片を製造することを可能にした。
【００１５】
パウダーの塩基度を１．１〜１．２としたのは、この範囲であればＡｌで還元された後の介在物中のＣａＯ：Ａｌ2Ｏ3比を最適な１．１３付近に保持することが可能であり、介在物の融点を低く保つことができるからである。塩基度を１．１以上とすることで介在物の融点を十分に低くすることができ、また塩基度を１．２以下とすることで介在物の融点を十分に低くすることができるとともに粘度の低下しすぎを抑制することができる。
【００１６】
パウダーの１３００℃での粘度を３ｐｏｉｓｅ以上としたのは、これによって連続鋳造時のパウダー巻き込みを低減することが可能だからである。また粘度を１０ｐｏｉｓｅ以下としたのは、この範囲であれば鋳型と凝固シェルの間隙へのパウダー流入が適正に行われ、鋳片の鋳型との潤滑が正常に保たれるからである。粘度を１０ｐｏｉｓｅ未満とするとより好ましい。
【００１７】
パウダーの粘度を上記のような高粘度に保持しつつ、塩基度を１．１〜１．２の範囲とするための手段として、本発明においては、ＺｒＯ2：１〜７質量％とＢ2Ｏ3：１〜７質量％の一方又は両方を含有することとすると好ましい。ＺｒＯ2やＢ2Ｏ3にはパウダーの粘度を上昇させる働きがあり、塩基度１．１以上の高塩基度でありながら高粘性を実現することが可能になる。
【００１８】
ＺｒＯ2含有量を１％以上としたのは、これによってＺｒＯ2によるパウダーの粘度上昇効果を得ることができるからであり、７％以下としたのは、さらに添加量を増やすとＺｒＯ2の大きな結晶が析出しパウダーの特性が不均一になるからである。ＺｒＯ2含有量は３〜７％とするとより好ましい。
【００１９】
Ｂ2Ｏ3含有量を１％以上としたのは、これによってＢ2Ｏ3によるパウダーの粘度上昇効果を得ることができるからであり、７％以下としたのは、さらに添加するとパウダーの融点が低下し鋳型内伝熱が不良になるからである。Ｂ2Ｏ3含有量は３〜７％とするとより好ましい。
【００２０】
本発明のモールドパウダーは、ＣａＯ、ＳｉＯ2を主成分とし、好ましくは上記の通りＺｒＯ2とＢ2Ｏ3の一方または両方を含む。さらに、凝固温度や粘度等を調整するために、例えばＡｌ2Ｏ3、Ｎａ2Ｏ、Ｆ、ＭｇＯ、Ｌｉ2Ｏ等を添加することができる。これらの成分の添加量は、この発明で規定している要件を具備する範囲内で目的に応じ所望量を任意に選べばよい。なお、これらの添加物は、従来のモールドパウダーに含まれているものである。
【００２１】
Ａｌ2Ｏ3含有量は２〜１０％の範囲が好ましい。Ａｌ2Ｏ3が高すぎるとパウダーの粘度を上げることができるが、溶鋼と反応した後のＣａＯ：Ａｌ2Ｏ3比が低くなり介在物の融点が高くなる。Ａｌ2Ｏ3が低すぎるとパウダーの凝固温度が高くなり鋳型潤滑不良を招く。
【００２２】
介在物中にＺｒＯ2が含有されていると、介在物の破砕性が向上する効果が生まれる。介在物中において、ＺｒＯ2は樹枝状晶として微細に析出するため、非常に容易に破砕されるのである。従って、ＺｒＯ2を含有するモールドパウダーについては、介在物の破砕性を良好にするためのパウダーのＣａＯ／ＳｉＯ2比率範囲を１．１〜１．２から１．０〜１．２の範囲に拡大する効果を有する。
【００２３】
本発明の鋼の連続鋳造用パウダーは、上記知見に基づき、ＣａＯ／ＳｉＯ2が１．０〜１．２の範囲であり、ＺｒＯ2：１〜７質量％を含有し、１３００℃における粘度が３〜１０ｐｏｉｓｅであることとすることにより、良好な結果を得ることができた。
【００２４】
ＺｒＯ2含有量を１％以上としたのは、これによりＺｒＯ2の介在物破砕性改善効果を発揮することができ、塩基度の下限を１．１から１．０に拡大することが可能になるからである。７％以下としたのは、それ以上添加すると微細ではなく巨大なＺｒＯ2結晶が晶出するからである。ＺｒＯ2は、塩基度を確保しつつ粘度を上昇させる効果をも有する。ＺｒＯ2含有量は３〜７％とするとより好ましい。塩基度の上限、粘度の範囲については、前記本発明の限定理由と同様の理由による。
【００２５】
上記本発明はさらに、Ｂ2Ｏ3：１〜７質量％を含有することとすると好ましい。Ｂ2Ｏ3は塩基度を確保しつつ粘度を上昇させる効果を有するからである。Ｂ2Ｏ3含有量は３〜７％とするとより好ましい。
【００２６】
本発明のモールドパウダーは、極低炭Ａｌキルド鋼の連続鋳造に用いると好適である。極低炭Ａｌキルド鋼とは、炭素濃度が０．０１質量％以下であり、さらに、Ｓｉ：０．０３％以下、Ａｌ：０．０１〜０．０６％である。
【００２７】
本発明においてはさらに、本発明のモールドパウダーを使用しつつ鋳型内の電磁攪拌を用いると好ましい。電磁攪拌によって、鋳型内への溶鋼の供給に伴う必然的に生じる溶鋼流動とは独立に鋳型内溶鋼に流動を付与することで、熱の供給不足の部位に熱を供給し均一化することによって、パウダーの流入を促進して、高粘度パウダーを用いてより高速での鋳造が可能となる。また、電磁攪拌によってメニスカス近傍の溶鋼流れの淀み部をなくすことができ、淀み部起因のパウダー流入不良をも解消することができる。本発明では十分に粘性の高いパウダーを使用することが可能なので、電磁攪拌によって溶鋼流動が増大してもパウダー巻き込みが増えるおそれはない。
【００２８】
電磁攪拌を行うとともに本発明の高粘度のパウダーを用いることで、パウダーの巻き込みなしに攪拌推力を増加させて溶鋼流速を上げることが可能となり、鋳型内に侵入してきた介在物の凝固シェルへの捕捉防止が可能となり、パウダー系以外の欠陥、例えばタンディッシュから持ち込まれたスラグやアルミナ等の介在物も低減する。
【００２９】
【実施例】
転炉にて溶製した溶鋼３００ｔｏｎを、ＲＨにて所定の成分濃度に調整した極低炭素鋼の溶鋼を、タンディッシュ、浸漬ノズルを介して垂直曲げ型の連続鋳造機で、厚み２５０ｍｍ、幅１６００ｍｍの鋳片に鋳造した。溶鋼成分範囲を表１に示す。鋳造速度を１．５ｍ／ｍｉｎとした。鋳片は１２００℃で加熱した後に通常の方法で熱間圧延を行い、さらに冷間で圧延した。
【００３０】
【表１】
鋳造に使用した連続鋳造用パウダーの成分、性質及び鋳造結果を表２に示す。
【００３２】
パウダーの粘性は１３００℃での粘性を用いた。粘度測定にあたっては、回転円筒法を用いた。測定対象パウダーを７００℃にて６０分間脱炭処理した試料を黒鉛坩堝に挿入し１４００℃にて１０〜１５分間予備溶解した後鉄坩堝に移し、縦型管状炉（エレマ炉）に入れ、Ｅ型粘度計のローターをスラグ中に浸漬し、１３００℃で３０分間安定させた後、ローターを回転させ粘性抵抗によるトルクを測定し、粘度を求めた。なおＥ型粘度計は事前に標準粘度液にて較正しておく。
【００３３】
介在物個数については、鋳片の介在物集積帯にあたる部位（表面から４０〜５０ｍｍ）から鋳片（１ｋｇ）を切り出して、スライム溶解法によって鉄を溶解し、介在物を抽出した。介在物の個数測定にあたってはアルミナクラスターは無視し、球形のパウダー系介在物のみをカウントした。
【００３４】
介在物組成については、スライム法によって抽出した介在物を樹脂に埋め込み、ＳＥＭ−ＥＤＸ法によって介在物組成の定量分析を行った。
【００３５】
プレス割れ成績については、製品となった０．８ｍｍ厚の鋼板を、１００ｍｍφの球状のダイを用いて３２ｍｍ張り出させたときの割れ発生枚数比率を評点化し、プレス割れ評点とした。プレス割れ評点は、プレス割れ発生枚数比率０．２％未満を◎◎、プレス割れ発生枚数比率０．２％以上１％未満を◎、プレス割れ発生枚数率１％以上３％未満を○、プレス割れ発生枚数率３％以上５％未満を△、プレス割れ発生枚数率５％以上を×とした。
【００３６】
【表２】
本発明例Ｎｏ．１、３は、パウダー中にＺｒＯ2あるいはＺｒＯ 2 及びＢ2Ｏ3を含有させ、パウダーの塩基度を１．１１以上としつつパウダーの粘度を３．５ｐｏｉｓｅ以上としているものである。鋳片へのパウダー巻き込みは非常に少なく、なおかつ鋳片に巻き込まれた介在物中のＣａＯ／Ａｌ2Ｏ3比が０．９８と高いので、製造した鋼板のプレス割れ成績は非常に良好であった。特に本発明例Ｎｏ．３は、ＺｒＯ2とＢ2Ｏ3を両方含有した結果として、粘度を４．６まで上昇させることができ、パウダー巻き込みによる介在物の個数が極めて少なく、結果としてプレス割れ評点も最も良好な結果であった。
【００４０】
比較例Ｎｏ．６は、パウダーの塩基度が１．０以上１．１未満であり、パウダーの粘度を３ｐｏｉｓｅ以上とし、ＺｒＯ2を含有していない。その結果、介在物組成におけるＣａＯ／Ａｌ2Ｏ3比はやや低く、プレス割れ評点がやや劣る結果となっている。
【００４１】
比較例Ｎｏ．７、８は、粘度を４ｐｏｉｓｅとしてパウダー巻き込みの低減を図っているが、パウダー塩基度が１未満であり、パウダー巻き込み起因の介在物組成におけるＣａＯ／Ａｌ2Ｏ3比が低く、プレス割れ評点が△という結果であった。
【００４２】
比較例Ｎｏ．９、１０は、パウダー塩基度は１．１以上であるが、パウダー粘度が２ｐｏｉｓｅ以下の非常に低い粘度であり、鋳造中におけるパウダー巻き込みに起因して介在物個数が極めて多く、その結果としてプレス割れ評点も×であって非常に悪い結果となった。
【００４３】
本実施例においては垂直曲げ型連続鋳造設備を使用したが、湾曲型及び垂直型連続鋳造設備においても同様の効果が得られる。
【００４４】
また、本実施例では自動車用の薄鋼板用の鋳片製造にあたっての例で述べたが、本技術の本質とするところは、パウダーの巻き込みによって生じる欠陥を防止することであり、缶用鋼板、鋼管など他の鋼種の鋳片を製造する場合にも有効である。
【００４５】
【発明の効果】
本発明の鋼の連続鋳造用パウダーは、１３００℃での粘度を３ｐｏｉｓｅ以上に確保しつつ塩基度を１．１〜１．２の範囲とすることにより、鋳造中のパウダー巻き込みの低減と、パウダー巻き込みに起因する介在物の破砕性の向上を両立させ、プレス割れの少ない良好な品質の鋼製品を製造可能にする。
【００４６】
本発明の鋼の連続鋳造用パウダーはまた、ＺｒＯ2を含有して１３００℃での粘度を３ｐｏｉｓｅ以上に確保しつつ塩基度を１．０〜１．２の範囲とすることにより、同様の効果を得ることができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a powder for continuous casting of steel added to a mold in continuous casting of steel.
[0002]
[Prior art]
In continuous casting of steel, powder for continuous casting is added on the surface of molten steel poured into a mold. The powder for continuous casting is also called mold powder or simply powder, and is heated and melted by high-temperature molten steel and flows between the mold and the solidified shell. The powder is mainly used for heat insulation and oxidation prevention on the molten steel surface in the mold, absorption of non-metallic inclusions floating from the molten steel, lubrication by the slag film flowing between the mold and the solidified shell, and heat removal from the slab by this film. The purpose is to control. As a result, a slab having excellent surface properties is obtained, and the molten powder is not easily caught in the molten steel, thereby producing a normal and good slab.
[0003]
By the way, during continuous casting operation, the molten steel injected flow into the mold is disturbed by the molten steel injected near the meniscus due to local fluctuations in the molten metal surface due to the operating conditions or changes in the operating conditions. In some cases, the powder is entangled in the molten steel and adheres to the solidified shell. In particular, in high-speed continuous casting, the flow rate of the injection flow increases, so that it becomes easy to entrain powder. If rolling is performed while the entrained powder is still attached to the slab, it will be stretched and cause surface defects in the cold-rolled steel sheet. Is required to have
[0004]
It is known that by using a highly viscous powder, it is possible to prevent the entrainment of the powder due to the molten steel flow in the mold, and to reduce the occurrence of defects due to the entrainment of the powder. In particular, IF steel (Interstitial Free steel) having a carbon concentration of 0.01% by mass or less is liable to cause surface defects of slabs and cold-rolled steel sheets due to powder entrainment. In ultra-low carbon steel, the claw at the tip of the solidified shell generated near the surface of the molten steel during casting tends to be long, and this claw is considered to cause powder entrainment.
[0005]
Patent Document 1 describes that, as a mold powder for extremely low carbon steel, the powder powder at 1300 ° C. has a viscosity of 3 poise or more, so that the entrainment of mold powder can be reduced even in high-speed casting.
[0006]
[Patent Document 1]
JP-A-10-263767 [0007]
[Problems to be solved by the invention]
By using a highly viscous powder having a viscosity of 3 poise or more as a mold powder for extremely low carbon steel, it has become possible to reduce the frequency of the mold powder being entrained in the molten steel. However, powder entrainment in the slab is not completely eliminated. As a result of increasing the viscosity of the mold powder, a phenomenon has occurred in which part of the entrained powder tends to cause press cracking when a steel sheet produced using this cast piece is press-formed.
[0008]
An object of the present invention is to provide a powder for continuous casting of steel in which the partially entrained powder does not cause press cracking while preventing entrainment of powder in continuous casting of ultra-low carbon steel.
[0009]
[Means for Solving the Problems]
That is, the gist of the present invention is as follows.
(1) is in the range of CaO / SiO 2 is 1.11 ~1.2, ZrO 2: 1~7 wt%, Al 2 O 3: containing 2 to 10 wt%, a viscosity at 1300 ° C. is 3. A powder for continuous casting of steel, characterized in that it is used for continuous casting of ultra-low-carbon Al-killed steel having an Al content of 0.01 to 0.06% by mass with 5 to 10 poise.
(2) The powder for continuous casting of steel according to (1) above, further containing B 2 O 3 : 1 to 7% by mass .
[0010]
DETAILED DESCRIPTION OF THE INVENTION
In continuous casting of ultra-low-carbon Al killed steel, the powder entrained in the molten metal is reduced in its constituent SiO 2 by Al in the molten steel, and Al 2 O 3 is generated instead. It becomes a binary inclusion of Al 2 O 3 . CaO-Al 2 O 3 in binary inclusions CaO: Looking at the relationship between the melting point of Al 2 O 3 ratio and inclusions, CaO: Al 2 O 3 ratio of the melting point of inclusions in the vicinity 1.1 The lowest.
[0011]
Conventionally, in order to increase the viscosity of the mold powder and increase the viscosity at 1300 ° C. to 3 poise or more, it has been realized by setting the basicity (CaO / SiO 2 ) in the powder component to a low basicity of about 0.8. . When powder with low basicity and high SiO 2 content is entrained in molten steel, there is much SiO 2 that should be reduced by Al to become Al 2 O 3 , so there is a high Al 2 O 3 content and CaO: Al 2 O 3 CaO—Al 2 O 3 inclusions with a ratio of less than 1.1. Inclusions having such a composition have a high melting point, and the inclusions are less likely to be crushed in the subsequent rolling stage. Conventionally, the use of high-viscosity powder reduces powder entrainment, but it is not completely absent. Inclusions caused by entrainment of powder cause press cracking. Was the cause.
[0012]
On the other hand, if the basicity of the powder can be increased while ensuring the 1300 ° C. viscosity of the powder at 3 poise or more, the content of SiO 2 in the powder decreases, and the CaO: Al 2 in the inclusion after reduction with Al As the O 3 ratio increases, a value near CaO: Al 2 O 3 = 1.1 having the lowest melting point can be realized.
[0013]
Al 2 O 3 in the powder also increases due to the floating of alumina as a deoxidation product, but the increase is negligibly small. Similarly, the powder is a combination of alumina inclusions and powder inclusions in molten steel. The increase in Al 2 O 3 in the system inclusions is also very small.
[0014]
The present invention has been made based on the above findings, and by setting the basicity (CaO / SiO 2 ) in the range of 1.1 to 1.2 while the viscosity at 1300 ° C. is 3 to 10 poise, Reduced powder entrainment in continuous casting of ultra-low carbon steel, produced inclusions with a low melting point even when entrained in molten steel, making it possible to produce good quality slabs with few press cracks .
[0015]
If the basicity of the powder is set to 1.1 to 1.2, the CaO: Al 2 O 3 ratio in the inclusion after reduction with Al is maintained in the vicinity of the optimum 1.13 within this range. This is because the melting point of the inclusion can be kept low. When the basicity is 1.1 or more, the melting point of the inclusion can be sufficiently lowered, and when the basicity is 1.2 or less, the melting point of the inclusion can be sufficiently lowered and the viscosity is increased. Can be suppressed.
[0016]
The reason why the viscosity of the powder at 1300 ° C. is set to 3 poise or more is that it is possible to reduce powder entrainment during continuous casting. The reason why the viscosity is set to 10 poise or less is that if it is within this range, the powder is properly introduced into the gap between the mold and the solidified shell, and the slab mold is properly lubricated. More preferably, the viscosity is less than 10 poise.
[0017]
In the present invention, ZrO 2 : 1 to 7% by mass and B 2 are used as means for keeping the basic viscosity within a range of 1.1 to 1.2 while maintaining the viscosity of the powder as described above. It is preferable to include one or both of O 3 : 1 to 7% by mass. ZrO 2 and B 2 O 3 have a function of increasing the viscosity of the powder, and it is possible to realize a high viscosity while having a high basicity of 1.1 or more.
[0018]
The reason why the ZrO 2 content is 1% or more is that it is possible to obtain the effect of increasing the viscosity of the powder by ZrO 2 , and the reason why the ZrO 2 content is 7% or less is that when the addition amount is further increased, the ZrO 2 content increases. This is because crystals precipitate and the characteristics of the powder become non-uniform. The ZrO 2 content is more preferably 3 to 7%.
[0019]
The reason why the B 2 O 3 content is set to 1% or more is that the effect of increasing the viscosity of the powder by B 2 O 3 can be obtained, and the reason why it is set to 7% or less is that the melting point of the powder when added further. This is because the heat transfer in the mold becomes poor. The B 2 O 3 content is more preferably 3 to 7%.
[0020]
The mold powder of the present invention contains CaO and SiO 2 as main components, and preferably contains one or both of ZrO 2 and B 2 O 3 as described above. Furthermore, for example, Al 2 O 3 , Na 2 O, F, MgO, Li 2 O and the like can be added to adjust the solidification temperature, viscosity, and the like. The amount of these components to be added may be arbitrarily selected according to the purpose within the range satisfying the requirements defined in the present invention. These additives are included in conventional mold powders.
[0021]
The Al 2 O 3 content is preferably in the range of 2 to 10%. If the Al 2 O 3 is too high, the viscosity of the powder can be increased, but the CaO: Al 2 O 3 ratio after reacting with the molten steel is lowered and the melting point of the inclusion is increased. If Al 2 O 3 is too low, the solidification temperature of the powder becomes high, resulting in poor mold lubrication.
[0022]
When ZrO 2 is contained in the inclusion, an effect of improving the friability of the inclusion is produced. In the inclusions, ZrO 2 precipitates finely as dendritic crystals and is therefore very easily crushed. Therefore, for the mold powder containing ZrO 2 , the CaO / SiO 2 ratio range of the powder for improving the crushability of inclusions is in the range of 1.1 to 1.2 to 1.0 to 1.2. Has the effect of expanding.
[0023]
Based on the above knowledge, the powder for continuous casting of steel of the present invention has a CaO / SiO 2 range of 1.0 to 1.2, contains ZrO 2 : 1 to 7% by mass, and has a viscosity at 1300 ° C. A favorable result was able to be obtained by setting it as 3-10 poise.
[0024]
The reason why the ZrO 2 content is set to 1% or more is that the effect of improving the inclusion crushability of ZrO 2 can be exhibited, and the lower limit of basicity can be expanded from 1.1 to 1.0. Because it becomes. The reason why it is set to 7% or less is that when it is added more than that, a large ZrO 2 crystal is crystallized instead of being fine. ZrO 2 also has the effect of increasing the viscosity while ensuring basicity. The ZrO 2 content is more preferably 3 to 7%. About the upper limit of basicity and the range of a viscosity, it is based on the reason similar to the limitation reason of the said invention.
[0025]
The present invention preferably further contains B 2 O 3 : 1 to 7% by mass. This is because B 2 O 3 has the effect of increasing the viscosity while securing the basicity. The B 2 O 3 content is more preferably 3 to 7%.
[0026]
The mold powder of the present invention is preferably used for continuous casting of ultra-low carbon Al killed steel. The extremely low-carbon Al killed steel has a carbon concentration of 0.01% by mass or less, Si: 0.03% or less, and Al: 0.01-0.06%.
[0027]
In the present invention, it is further preferable to use electromagnetic stirring in the mold while using the mold powder of the present invention. By applying magnetic flow to the molten steel in the mold independently of the inevitably generated molten steel flow accompanying the supply of molten steel into the mold by electromagnetic stirring, by supplying heat to the insufficient heat supply site and making it uniform By promoting the inflow of the powder, it becomes possible to perform casting at a higher speed using the high viscosity powder. Moreover, the stagnation part of the molten steel flow in the vicinity of the meniscus can be eliminated by electromagnetic stirring, and the powder inflow failure caused by the stagnation part can be eliminated. In the present invention, a sufficiently viscous powder can be used. Therefore, even if the molten steel flow is increased by electromagnetic stirring, there is no possibility that the powder entrainment will increase.
[0028]
By performing the magnetic stirring and using the high viscosity powder of the present invention, it becomes possible to increase the stirring thrust without entraining the powder and increase the flow velocity of the molten steel, and the inclusions that have penetrated into the mold to the solidified shell Capturing can be prevented, and defects other than the powder system, for example, inclusions such as slag and alumina brought in from the tundish are reduced.
[0029]
【Example】
300ton of molten steel melted in a converter, adjusted to a predetermined component concentration with RH, is a continuous casting machine of vertical bending type through a tundish and immersion nozzle, with a thickness of 250mm, width Cast into a 1600 mm slab. The molten steel component range is shown in Table 1. The casting speed was 1.5 m / min. The slab was heated at 1200 ° C. and then hot-rolled by a normal method and further cold-rolled.
[0030]
[Table 1]
Table 2 shows the components, properties and casting results of the powder for continuous casting used for casting.
[0032]
The viscosity at 1300 ° C. was used as the viscosity of the powder. In measuring the viscosity, the rotating cylinder method was used. A sample obtained by decarburizing the powder to be measured at 700 ° C. for 60 minutes was inserted into a graphite crucible, preliminarily melted at 1400 ° C. for 10 to 15 minutes, transferred to an iron crucible, placed in a vertical tubular furnace (Elema furnace), and E The rotor of the type viscometer was immersed in slag and stabilized at 1300 ° C. for 30 minutes, and then the rotor was rotated to measure the torque due to viscous resistance to determine the viscosity. The E-type viscometer is calibrated with a standard viscosity solution in advance.
[0033]
As for the number of inclusions, a slab (1 kg) was cut out from a portion (40 to 50 mm from the surface) corresponding to the inclusion accumulation zone of the slab, and iron was dissolved by a slime dissolution method to extract inclusions. In measuring the number of inclusions, alumina clusters were ignored, and only spherical powder-type inclusions were counted.
[0034]
As for the inclusion composition, inclusions extracted by the slime method were embedded in the resin, and the inclusion composition was quantitatively analyzed by the SEM-EDX method.
[0035]
Regarding the press cracking results, the ratio of the number of cracks when the 0.8 mm-thick steel sheet as a product was extended by 32 mm using a spherical die of 100 mmφ was scored and used as a press crack score. The press crack score is ◎◎ when the ratio of press crack occurrence is less than 0.2%, ◎ When the ratio of press crack occurrence is 0.2% or more and less than 1%, ◎ When the ratio of press crack occurrence is 1% or more and less than 3%, ○ The crack generation number ratio of 3% or more and less than 5% was evaluated as Δ, and the press crack generation ratio of 5% or more was evaluated as ×.
[0036]
[Table 2]
Invention Example No. In Nos. 1 and 3, ZrO 2 or ZrO 2 and B 2 O 3 are contained in the powder, and the viscosity of the powder is 3.5 poise or more while the basicity of the powder is 1.11 or more. Since the powder entrainment in the slab is very small, and the CaO / Al 2 O 3 ratio in the inclusions entrained in the slab is as high as 0.98, the press cracking performance of the manufactured steel sheet was very good. It was. In particular, Invention Example No. 3 can increase the viscosity to 4.6 as a result of containing both ZrO 2 and B 2 O 3 , the number of inclusions due to powder entrainment is extremely small, and as a result, the press crack score is also the best Met.
[0040]
Comparative Example No. In No. 6, the basicity of the powder is 1.0 or more and less than 1.1, the viscosity of the powder is 3 poise or more, and ZrO 2 is not contained. As a result, the CaO / Al 2 O 3 ratio in the inclusion composition is slightly low, and the press crack score is slightly inferior.
[0041]
Comparative Example No. 7 and 8 are intended to reduce powder entrainment with a viscosity of 4 poise, but the powder basicity is less than 1, the CaO / Al 2 O 3 ratio in the inclusion composition resulting from powder entrainment is low, and the press crack rating is The result was Δ.
[0042]
Comparative Example No. Nos. 9 and 10 have a powder basicity of 1.1 or more, but a very low viscosity with a powder viscosity of 2 poise or less, and the number of inclusions is extremely high due to the entrainment of powder during casting. The crack score was x, which was very bad.
[0043]
Although the vertical bending type continuous casting equipment is used in this embodiment, the same effect can be obtained in the curved type and vertical type continuous casting equipment.
[0044]
Further, in this example, the example of manufacturing a slab for a thin steel sheet for automobiles was described, but the essence of the present technology is to prevent defects caused by entrainment of powder, It is also effective when producing slabs of other steel types such as steel pipes.
[0045]
【The invention's effect】
The powder for continuous casting of the steel of the present invention reduces powder entrainment during casting by maintaining the viscosity at 1300 ° C. to 3 poise or more and the basicity in the range of 1.1 to 1.2. It is possible to improve the friability of inclusions caused by entrainment and to manufacture steel products of good quality with few press cracks.
[0046]
The steel continuous casting powder of the present invention also contains ZrO 2 and has the same effect by keeping the viscosity at 1300 ° C. at 3 poise or higher and the basicity in the range of 1.0 to 1.2. Can be obtained.
Claims (2)
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| KR100623908B1 (en) * | 2004-06-23 | 2006-09-19 | 스톨베르그 앤드 삼일 주식회사 | Fluorine-free mold flux for the continuous casting of steel and method for producing the same |
| JP4626522B2 (en) * | 2006-01-11 | 2011-02-09 | 住友金属工業株式会社 | Mold powder for continuous casting and continuous casting method for plain steel |
| JP5226423B2 (en) * | 2008-08-12 | 2013-07-03 | 日鐵住金建材株式会社 | Powder for continuous casting of steel |
| KR20120092708A (en) * | 2010-01-21 | 2012-08-21 | 신닛뽄세이테쯔 카부시키카이샤 | Mould powder for continuous casting of steel |
| CN107282903B (en) * | 2016-12-30 | 2019-04-05 | 西峡龙成冶金材料有限公司 | A kind of continuous super low carbon steel casting crystallizer protecting residue |
| CN112756573B (en) * | 2020-12-24 | 2022-06-17 | 芜湖新兴铸管有限责任公司 | Casting powder for engineering machinery bucket tooth steel and preparation method thereof |
| JP7464865B2 (en) | 2022-06-17 | 2024-04-10 | 品川リフラクトリーズ株式会社 | Mold powder and method for continuous casting of steel using same |
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| EXPY | Cancellation because of completion of term |