JP4592974B2

JP4592974B2 - Continuous casting method of molten steel for non-oriented electrical steel sheet and slab for non-oriented electrical steel sheet

Info

Publication number: JP4592974B2
Application number: JP2001037480A
Authority: JP
Inventors: 昌文瀬々; 隆諸星
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 2001-02-14
Filing date: 2001-02-14
Publication date: 2010-12-08
Anticipated expiration: 2021-02-14
Also published as: JP2002241831A

Description

【０００１】
【発明の属する技術分野】
本発明は、凝固組織が微細な等軸晶を備え、割れや中心偏析、センターポロシティ等の内部欠陥がなく、品質に優れ、しかも、凝固後にＭｎＳが分散析出するのを抑制することができる無方向性電磁鋼板用溶鋼の連続鋳造方法及び無方向性電磁鋼板用鋳片に関する。
【０００２】
【従来の技術】
従来、鋳片は、溶鋼から造塊法や連続鋳造法により、スラブ、ブルーム、ビレット、薄鋳片等を鋳造し、これを所定のサイズに切断して製造されている。
また、鋼材は、前記した鋳片を加熱炉等を用いて加熱した後、粗圧延や仕上げ圧延等を施すことにより、鋼板や形鋼等に加工される。
しかし、この鋳片は、凝固するまでの過程において、凝固組織が柱状晶等の大きな結晶組織になるため、内部の凝固収縮時の負圧に起因するセンターポロシティ（ザク）、バルジングや前記凝固収縮時の負圧に起因する中心偏析、あるいは溶鋼が冷却されて凝固する過程で、凝固シェル（凝固殻）に加わる歪みに起因する内部割れ等の内部欠陥が生じる。
こうして、鋳片に発生した内部欠陥は、圧延後も鋼材に残存するため、鋼材の品質を低下させ、場合によっては製品として使用できなくする（屑化）等の問題を生じさせる。
【０００３】
この対策として、鋳片の凝固組織を微細な等軸晶（結晶粒）にし、鋳片と、その鋳片を加工して得られる鋼材の表面及び内部欠陥を防止する方法が試みられている。
鋳片の凝固組織を等軸晶化する方法としては、１）溶鋼の温度を低くして低温鋳造する方法、２）凝固過程の溶鋼を電磁攪拌する方法、３）溶鋼が凝固する際に凝固核となる金属酸化物を添加する方法、又は、これ等１）〜３）を組合せて行う方法が知られている。
低温鋳造の具体例としては、例えば特公平７−８４６１７号公報に記載されているように、溶鋼を連続鋳造する際、過熱温度（実際の溶鋼温度からこの溶鋼の液相線温度を差し引いた温度）を４０℃以下にし、鋳型内で溶鋼を冷却しながら鋳型から引き抜き、凝固した鋳片の等軸晶の割合を７０％以上にして、フェライト系ステンレス鋼板に発生するリジングを防止する方法が提案されている。
更に、溶鋼の電磁攪拌については、特開昭５０−１６６１６号公報に記載されているように、凝固過程の溶鋼に電磁攪拌を行って、成長する柱状晶を抑制することで、鋳片の凝固組織の等軸晶を６０％以上にしてクロムを含むフェライト系ステンレス鋼に発生するリジングを防止する方法が提案されている。
また、特開昭５３−９０１２９号公報に記載されているように、溶鋼が凝固する際に凝固核となる金属酸化物の添加と電磁攪拌を組合せることで、鋳片の厚み方向の全断面の凝固組織を殆ど等軸晶にする方法が提案されている。
【０００４】
【発明が解決しようとする課題】
しかしながら、特公平７−８４６１７号公報の方法では、過熱温度が低いため、鋳造途中で溶鋼が凝固し、溶鋼を鋳型に注湯するノズルの詰まりや鋳型内湯面の皮張りを生じて鋳造が困難になる。
更に、溶鋼の粘性が増加するため、介在物の浮上が阻害されて介在物に起因した欠陥等が発生する等から、十分な等軸晶を備えた鋳片を製造できる程度の低い過熱温度にすることが困難である。
また、特開昭５０−１６６１６号公報の方法では、鋳片の表面層の凝固組織を改善してリジング等の表面欠陥の発生を抑制できるものの、鋳片の表面層から内部にわたって凝固組織を均一な等軸晶にすることが難しく、内部に割れや中心偏析、センターポロシティ等を発生させる場合がある。
この鋳片の内部の凝固組織を改善するため、電磁攪拌装置を多段に配置して、内部の溶鋼を攪拌する方法も考えられるが、設備制約から設置そのものが困難であり、しかも、多大の設備費用を伴う等の問題もある。
更に、特開昭５３−９０１２９号公報では、鋳型内の溶鋼に、Ｃｏ、Ｂ、Ｍｏ、Ｖ、Ｎｉ等の酸化物を添加している。これ等の酸化物は、低炭素やフェライト系ステンレス等の溶鋼の場合に凝固組織の接種核として有効に作用して等軸晶を増加させるが、無方向性電磁鋼板の処理過程で生成するＭｎＳの鋳型内での微細分散を防止することができないため、この鋳片から製造された無方向性電磁鋼板の磁性（鉄損）を悪くさせる。これは、無方向性電磁鋼板の処理過程で生成する粒径１μｍ以下の微細なＭｎＳが、ピンニング粒子として作用し、熱処理過程における結晶粒の成長を阻害するからである。
このように、従来の方法では、δ−Ｆｅが凝固初晶である無方向性電磁鋼板用の鋳片の凝固組織を均一な等軸晶にすることができず、鋳片に発生する内部欠陥を防止することが困難であり、しかも、ＭｎＳが微細分散析出するため、結晶粒が微細になり過ぎて無方向性電磁鋼板の鉄損を低下させるといった問題を解決することができない。
【０００５】
本発明はかかる事情に鑑みてなされたもので、凝固組織を均一な等軸晶にし、内部割れや中心偏析、センターポロシティ等に起因する鋳片や鋼板の内部欠陥を防止し、凝固後にＭｎＳが微細分散析出するのを抑制して磁性を向上させることができる無方向性電磁鋼板用溶鋼の連続鋳造方法及びその鋳片を提供することを目的とする。
【０００６】
【課題を解決するための手段】
前記目的に沿う本発明の無方向性電磁鋼板用溶鋼の連続鋳造方法は、無方向性電磁鋼板用の溶鋼を、該溶鋼中に含まれるＭｇ質量％、Ｏ質量％、Ｓ質量％、Ｍｎ質量％が下式を満たすように調整（但し、Ｃｒを０．４〜５質量％含む場合を除く）した後、この調整した溶鋼を連続鋳造している。
（Ｍｇ質量％−１．５×Ｏ質量％）×（Ｓ質量％）＞１．２×１０^-6
かつ
（Ｍｇ質量％−１．５×Ｏ質量％）＞１／２００×（Ｍｎ質量％）
なお、Ｍｇ質量％は溶鋼中に含まれるＭｇ質量％、Ｏ質量％は溶鋼中に含まれるＯ質量％、Ｓ質量％は溶鋼中に含まれるＳ質量％、Ｍｎ質量％は溶鋼中に含まれるＭｎ質量％である。
この方法により、溶鋼中のＯとＭｇを反応させ、ＭｇＯ、ＭｇＯ・Ａｌ2Ｏ3を生成させて溶鋼中に分散させ、これを溶鋼が凝固する際の接種核として作用させることができ、分散させた接種核を起点に溶鋼を凝固させるので、鋳片の凝固組織を均一な等軸晶にでき、鋳片の内部割れや中心偏析、センターポロシティ等の内部欠陥の発生を防止することができる。
【０００７】
前記目的に沿う本発明に係る無方向性電磁鋼板用鋳片は、無方向性電磁鋼板用の溶鋼を、該溶鋼中に含まれるＭｇ質量％、Ｏ質量％、Ｓ質量％、Ｍｎ質量％が下式を満たすように調整（但し、Ｃｒを０．４〜５質量％含む場合を除く）した後、この調整した溶鋼を連続鋳造し、該溶鋼が凝固を開始する温度以上の温度で該溶鋼中にＭｇＯを生成させ、しかも、ＭｎＳが析出を開始するより前にＭｇＳを生成させた後、該ＭｇＳの周囲にＭｎＳを析出させる。
（Ｍｇ質量％−１．５×Ｏ質量％）×（Ｓ質量％）＞１．２×１０ ^-6
かつ
（Ｍｇ質量％−１．５×Ｏ質量％）＞１／２００×（Ｍｎ質量％）
なお、Ｍｇ質量％は溶鋼中に含まれるＭｇ質量％、Ｏ質量％は溶鋼中に含まれるＯ質量％、Ｓ質量％は溶鋼中に含まれるＳ質量％、Ｍｎ質量％は溶鋼中に含まれるＭｎ質量％である。
この鋳片は、ＭｇＯ、ＭｇＯ・Ａｌ2Ｏ3等のＭｇ酸化物を、溶鋼が凝固する際の接種核として活用するため、鋳片の凝固組織を均一な等軸晶にして内部欠陥の発生を防止することができる。しかも、凝固過程でＭｇＳの周囲にＭｎＳを析出させ、母相（最初の凝固組織）中での微細なＭｎＳの析出を防止するので、ＭｎＳの微細分散による結晶粒の微細化を抑制して結晶粒の成長を促進する。
従って、この鋳片から製造した鋼材の磁性（鉄損）を向上させることができる。
【０００８】
【発明の実施の形態】
続いて、添付した図面を参照しつつ、本発明を具体化した実施の形態につき説明し、本発明の理解に供する。
図１は本発明の一実施の形態に係る無方向性電磁鋼板用溶鋼の連続鋳造方法に用いる連続鋳造装置の全体断面図である。
図１に示すように、本発明の一実施の形態に係る無方向性電磁鋼板用溶鋼の連続鋳造方法に用いる連続鋳造装置１０は、図示しない金属マグネシウム（Ｍｇ）材料の一例であるＭｇワイアを添加した溶鋼１１を貯湯したタンディッシュ１２と、タンディッシュ１２の底部に取付けられた浸漬ノズル１３と、浸漬ノズル１３を介して、下側に流れる溶鋼１１を注湯する鋳型１４を有し、鋳型１４の下方には、図示しない冷却水ノズルを設けた支持セグメント１５と、溶鋼１１が凝固殻１６ａを形成した鋳片１６を圧下する圧下セグメント１７と、鋳片１６を所定の速度で引き抜くための一対のピンチロール１８を備えている。
【０００９】
次に、連続鋳造装置１０を適用した無方向性電磁鋼板用溶鋼の連続鋳造方法及び連続鋳造された無方向性電磁鋼板用鋳片について説明する。
無方向性電磁鋼板用の溶鋼１１を、図示しない取鍋に受湯した後、サンプリングして、Ｏ質量％とＳ質量％を測定し、この値を基に、金属Ｍｇワイアを添加した際のＭｇ歩留りから溶鋼１１中のＭｇ質量％を求め、溶鋼１１に含まれるＭｇ濃度（質量％）、Ｓ質量％、Ｍｎ質量％、Ｏ質量％が下式を満足するように調整した後、この調整した溶鋼１１を連続鋳造する。
（Ｍｇ質量％−１．５×Ｏ質量％）×（Ｓ質量％）＞１．２×１０^-6
かつ
（Ｍｇ質量％−１．５×Ｏ質量％）＞１／２００×（Ｍｎ質量％）
なお、Ｍｇ質量％は溶鋼中に含まれるＭｇ質量％、Ｏ質量％は溶鋼中に含まれるＯ質量％、Ｓ質量％は溶鋼中に含まれるＳ質量％、Ｍｎ質量％は溶鋼中に含まれるＭｎ質量％である。
前記式において、（１．５×Ｏ質量％）は、溶鋼中の酸素がすべてＭｇＯとなった場合の化学量論的計算から求めた値であり、過剰に添加されたＭｇ質量％は、（Ｍｇ質量％−１．５×Ｏ質量％）で表される。また、この過剰に添加されたＭｇ質量％とＳ質量％の積を実験を行って求めた結果、濃度の積が１．２×１０^-6より大きければ安定してＭｇＳを生成することが分かった。
更に、ＭｎＳが生成（析出開始）するより前にＭｇＳを生成させるには、溶鋼中のＳと結合する前記過剰のＭｇ質量％を、溶鋼中のＭｎ質量％の１／２００倍より大きくする。これにより、ＭｇＳをＭｎＳに対し優先して析出させる。
【００１０】
Ｍｇを添加し、タンディッシュ１２に貯湯された溶鋼１１は、タンディッシュ１２の底部に設けた浸漬ノズル１３を介して鋳型１４に注湯され、鋳型１４による冷却と、支持セグメント１５に布設された冷却水ノズルからの散水によって冷却されて凝固殻１６ａを形成し、支持セグメント１５の下流側に進むにつれて、冷却水の散水により抜熱される。
この抜熱によって順次凝固殻１６ａの厚みを増した鋳片１６は、支持セグメント１５の下流側に配置された圧下セグメント１７により、１〜１０ｍｍの押し込み量で圧下された後、完全に凝固する。
凝固した鋳片１６の内部には、溶鋼１１の温度が低下して凝固を開始する前の温度、即ち、溶鋼１１が凝固を開始する温度以上の温度で、ＭｇＯやＭｇＯ・Ａｌ2Ｏ3を析出生成させており、また、このＭｇＯ、ＭｇＯ・Ａｌ2Ｏ3は、溶鋼１１が凝固する際に、接種核として作用するので、この周囲にδ−鉄が析出して均一な等軸晶（凝固組織）を形成することができる。
【００１１】
次に、溶鋼１１中のＯとの反応に消費されるＭｇ量よりも多量にＭｇを添加しているため、ＭｎＳが析出を開始する前に、過剰に添加されたＭｇが、溶鋼１１中のＳ（硫黄）と反応してＭｇＳを析出生成する。
析出したＭｇＳは、溶鋼１１中のＭｎＳの格子歪み（δ−ＦｅとＭｎＳの格子定数の差／δ−Ｆｅの格子定数の値）との差が小さく、ＭｇＳとＭｎＳの格子整合性が良好であるため、鋳片１６が連続鋳造装置１０内で冷却され、その温度が約１０００〜１２００℃になる領域で、ＭｇＳの周囲にＭｎＳが優先的に析出する。
これにより、母相中に微細なＭｎＳが微細分散析出するのを防止することができる。
この鋳片１６から製造した無方向性電磁鋼板は、微細分散するＭｎＳを予めＭｇＳの周囲に析出させるので、加熱焼鈍した際に鋳片１６中に分散するＭｎＳが少なくなり、微細なＭｎＳによるピンニング作用を大幅に抑制でき、結晶粒の成長を促進することができる。その結果、ＭｇＯとＭｇＳの相乗した働きにより、凝固組織を均一な等軸晶にし、しかも、ＭｎＳの微細分散析出を抑制しない場合よりも結晶粒を大きくした鋳片１６を鋳造することができる。
この鋳片１６は、内部に発生する内部割れや溶鋼流動に伴う中心偏析、センターポロシティ等の内部欠陥が無く、鋳片１６の手入れや屑化をなくして良鋳片の歩留り及び品質を向上させることができる。
このようにして鋳造された鋳片１６は、ピンチロール１８により引き抜かれて、図示しない切断機により所定のサイズに切断されてから圧延等の後工程に搬送される。
この鋳片１６に、圧延等の加工を施した無方向電磁鋼板においても、内部欠陥及び表面疵やしわ等の表面欠陥の発生が防止でき、鋼板の手入れ等の解消や良製品歩留り等の向上が可能になる。
しかも、ＭｇＳの周囲に大きなＭｎＳを析出させているので、微細なＭｎＳによる鋳片１６中の結晶粒の極端な微細化が抑制されるため、優れた磁性（鉄損の低い）を得ることができる。
【００１２】
鋳片１６の介在物の種類と量は、鋳片１６の全断面の一部を切り出して、この切り出し片を一般に用いられている光学顕微鏡で観察することにより、測定することができる。
また、凝固組織は、鋳片１６をピクリン酸でエッチングして、デンドライト組織を検出し、この組織から等軸晶か、柱状晶かを判別することができる。
【００１３】
【実施例】
次に、本発明の一実施の形態に係る無方向性電磁鋼板用溶鋼の連続鋳造方法を用いて鋳造した鋳片の実施例について説明する。
主成分が表１に示す組成の無方向性電磁鋼板用の溶鋼３５０トンを取鍋に入れ、この溶鋼にＭｇワイアを添加して、溶鋼中のＭｇ濃度、Ｓ質量％、Ｍｎ質量％、Ｏ質量％をそれぞれ調整し、内寸が厚み２５０ｍｍ、幅１２００ｍｍの鋳型に鋳湯し、１．２ｍ／分の速度でピンチロールにより引き抜きいて鋳片を鋳造した。そして、鋳造した鋳片の凝固組織及び内部品質、鋼板の表面疵・しわ、磁気特性の良否について調査した。その結果を表２に示す。
実施例１〜５は、溶鋼中のＭｇ質量％、Ｓ質量％、Ｍｎ質量％、Ｏ質量％が本発明の前記した式の関係を満たす場合であり、いずれも凝固組織が等軸晶にでき、内部品質も割れや中心偏析、センターポロシティ等の内部欠陥が無く、この鋳片を加工した無方向性電磁鋼板の表面疵・しわの発生が無く良好であり、磁気特性も良好な結果が得られた。
【００１４】
【表１】

【００１５】
【表２】

【００１６】
これに対し、比較例１及び比較例２は、溶鋼にＭｇを添加したが、Ｍｇ質量％、Ｓ質量％、Ｍｎ質量％、Ｏ質量％が本発明の前記した式の関係を満たさない場合であり、ＭｎＳがＭｇＳよりも早く析出し、ＭｎＳを微細分散させてしまい、結晶粒の成長が阻害されて鋳片の結晶粒径が小さくなり、磁気特性も不良となった。
比較例３は、添加したＭｇが酸素に消費され、ＭｇＳを生成できなかった場合であり、微細なＭｎＳが鋳片中に分散して析出し、鋳片の結晶粒径が小さくなり、磁気特性が不良となった。
比較例４はＭｇの添加量が少ない場合、比較例５はＭｇが無添加の場合であり、いずれも凝固組織が柱状晶になり、内部欠陥、表面疵・しわ、磁気特性の全てが不良となった。
【００１７】
以上、本発明の実施の形態を説明したが、本発明は、上記した形態に限定されるものでなく、要旨を逸脱しない条件の変更等は全て本発明の適用範囲である。
例えば、鋳片は、連続鋳造の他に、造塊法やベルトキャスター、ロール等の鋳造法により鋳造することができる。
更に、ＭｇやＭｇ合金等を薄鋼で覆った線状に加工したワイアを添加する他に、Ｍｇ、又はＭｇ合金等を溶鋼に浸漬ランスを用いて吹き込んで添加することもできる。
【００１８】
【発明の効果】
請求項１記載の無方向性電磁鋼板用溶鋼の連続鋳造方法においては、無方向性電磁鋼板用の溶鋼を、溶鋼中に含まれるＭｇ質量％、Ｏ質量％、Ｓ質量％、Ｍｎ質量％が所定の範囲を満たすように調整した後、この調整した溶鋼を連続鋳造しているので、溶鋼が凝固した鋳片の凝固組織を均一な等軸晶にして内部欠陥を抑制し、鋳片の手入れや屑化を防止して良好な鋳片の歩留りを向上でき、鋳片の品質を高めることができる。
【００１９】
請求項２記載の無方向性電磁鋼板用鋳片においては、無方向性電磁鋼板用の溶鋼を、溶鋼中に含まれるＭｇ質量％、Ｏ質量％、Ｓ質量％、Ｍｎ質量％が所定の範囲を満たすように調整した後、この調整した溶鋼を連続鋳造し、溶鋼が凝固を開始する温度以上の温度でＭｇＯを生成させ、しかも、ＭｎＳが析出を開始するより前にＭｇＳを生成させた後、ＭｇＳの周囲にＭｎＳを析出させているので、均一な等軸晶を備えて内部欠陥及び表面疵等を防止して製品の歩留りを高め、ＭｇＳの周囲にＭｎＳを粗大に析出させて結晶粒の成長を促進して無方向性電磁鋼板の磁性を安定して向上させることができる。
【図面の簡単な説明】
【図１】本発明の一実施の形態に係る無方向性電磁鋼板用溶鋼の連続鋳造方法に用いる連続鋳造装置の全体断面図である。
【符号の説明】
１０：連続鋳造装置、１１：溶鋼、１２：タンディッシュ、１３：浸漬ノズル、１４：鋳型、１５：支持セグメント、１６：鋳片、１６ａ：凝固殻、１７：圧下セグメント、１８：ピンチロール[0001]
BACKGROUND OF THE INVENTION
The present invention has fine equiaxed crystals in the solidified structure, has no internal defects such as cracks, center segregation, and center porosity, is excellent in quality, and can prevent MnS from being dispersed and precipitated after solidification. The present invention relates to a continuous casting method for molten steel for grain-oriented electrical steel sheets and a slab for non-oriented electrical steel sheets.
[0002]
[Prior art]
Conventionally, slabs are manufactured by casting slabs, blooms, billets, thin slabs and the like from molten steel by an ingot-making method or a continuous casting method, and cutting them into a predetermined size.
In addition, the steel material is processed into a steel plate, a shaped steel, or the like by subjecting the above-described cast slab to heating using a heating furnace or the like, followed by rough rolling, finish rolling, or the like.
However, in this slab, the solidification structure becomes a large crystal structure such as a columnar crystal in the process until solidification, so the center porosity (zaku), bulging and the solidification shrinkage due to the negative pressure during the solidification shrinkage inside In the process of central segregation due to negative pressure at the time, or in the process where the molten steel is cooled and solidified, internal defects such as internal cracks due to strain applied to the solidified shell (solidified shell) occur.
Thus, the internal defects generated in the slab remain in the steel material even after rolling, so that the quality of the steel material is lowered, and in some cases, the product cannot be used as a product (debris).
[0003]
As a countermeasure, a method has been attempted in which the solidification structure of the slab is made into fine equiaxed crystals (crystal grains), and the surface of the slab and the steel material obtained by processing the slab and internal defects are prevented.
The method of equiaxed crystallization of the solidified structure of the slab is as follows: 1) a method of low temperature casting by lowering the temperature of the molten steel, 2) a method of electromagnetically stirring the molten steel in the solidification process, and 3) solidification when the molten steel solidifies A method of adding a metal oxide as a nucleus or a method of combining these 1) to 3) is known.
As a specific example of low temperature casting, for example, as described in Japanese Patent Publication No. 7-84617, when continuously casting molten steel, a superheat temperature (a temperature obtained by subtracting the liquidus temperature of this molten steel from the actual molten steel temperature). ) Is 40 ° C or lower, the molten steel is pulled out from the mold while cooling in the mold, and the ratio of equiaxed crystals in the solidified slab is set to 70% or more to prevent ridging that occurs in ferritic stainless steel sheets. Has been.
Further, regarding electromagnetic stirring of molten steel, as described in JP-A-50-16616, electromagnetic stirring is performed on molten steel in the solidification process to suppress growing columnar crystals, thereby solidifying the slab. There has been proposed a method for preventing ridging that occurs in ferritic stainless steel containing chromium by setting the equiaxed crystal of the structure to 60% or more.
Further, as described in JP-A-53-90129, the entire cross section in the thickness direction of the slab can be obtained by combining the addition of a metal oxide that becomes a solidification nucleus and solidification when the molten steel solidifies. There has been proposed a method in which the solidification structure of this is almost equiaxed.
[0004]
[Problems to be solved by the invention]
However, in the method disclosed in Japanese Patent Publication No. 7-84617, since the superheating temperature is low, the molten steel solidifies during casting, and clogging of the nozzle for pouring the molten steel into the mold and skinning of the molten metal surface in the mold are difficult to cast. become.
Furthermore, since the viscosity of the molten steel increases, the rise of the inclusions is hindered and defects due to the inclusions occur, so that the superheat temperature is low enough to produce a slab with sufficient equiaxed crystals. Difficult to do.
Further, in the method disclosed in Japanese Patent Laid-Open No. 50-16616, the solidification structure of the surface layer of the slab can be improved to suppress generation of surface defects such as ridging, but the solidification structure is uniform from the surface layer of the slab to the inside. It is difficult to obtain equiaxed crystals, and cracks, center segregation, center porosity, etc. may occur inside.
In order to improve the solidification structure inside the slab, a method of agitating the molten steel inside by arranging electromagnetic stirrers in multiple stages is also conceivable, but installation itself is difficult due to equipment restrictions, and a lot of equipment There are also problems such as costs.
Furthermore, in JP-A-53-90129, an oxide such as Co, B, Mo, V, Ni or the like is added to the molten steel in the mold. These oxides effectively act as inoculation nuclei for the solidified structure in the case of molten steel such as low carbon and ferritic stainless steel, and increase equiaxed crystals, but MnS produced during the processing of non-oriented electrical steel sheets Since the fine dispersion in the mold cannot be prevented, the magnetism (iron loss) of the non-oriented electrical steel sheet produced from this slab is deteriorated. This is because fine MnS having a particle diameter of 1 μm or less generated in the process of processing the non-oriented electrical steel sheet acts as pinning particles and inhibits the growth of crystal grains in the heat treatment process.
As described above, in the conventional method, the solidification structure of the slab for the non-oriented electrical steel sheet in which δ-Fe is a solidified primary crystal cannot be formed into a uniform equiaxed crystal, and internal defects generated in the slab In addition, since MnS is finely dispersed and precipitated, it is impossible to solve the problem that the crystal grain becomes too fine and the iron loss of the non-oriented electrical steel sheet is reduced.
[0005]
The present invention has been made in view of such circumstances, making the solidification structure uniform isometric crystals, preventing internal defects of slabs and steel sheets due to internal cracks, center segregation, center porosity, etc. It aims at providing the continuous casting method of the molten steel for non-oriented electrical steel sheets which can suppress the fine dispersion | distribution precipitation, and can improve magnetism, and its slab.
[0006]
[Means for Solving the Problems]
The continuous casting method for molten steel for non-oriented electrical steel sheets according to the present invention, which meets the above-mentioned object, includes molten steel for non-oriented electrical steel sheets, Mg mass %, O mass %, S mass %, and Mn mass contained in the molten steel. % Is adjusted so as to satisfy the following formula (excluding the case where 0.4 to 5% by mass of Cr is included), and then the adjusted molten steel is continuously cast.
(Mg mass % −1.5 × O mass %) × (S mass %)> 1.2 × 10 ⁻⁶
And (Mg mass %-1.5 x O mass %)> 1/200 x (Mn mass %)
Incidentally, Mg mass% Mg mass% contained in the molten steel, O wt% O wt% is contained in the molten steel, S wt% S% by weight contained in the molten steel, Mn mass% is contained in the molten steel It is Mn mass %.
By this method, O and Mg in the molten steel are reacted to produce MgO, MgO.Al2O3 and dispersed in the molten steel, which can act as an inoculum nucleus when the molten steel solidifies. Since the molten steel is solidified starting from the nucleus, the solidified structure of the slab can be made uniform and equiaxed, and internal defects such as internal cracks, center segregation, and center porosity of the slab can be prevented.
[0007]
The slab for a non-oriented electrical steel sheet according to the present invention that meets the above-mentioned object is obtained by combining molten steel for a non-oriented electrical steel sheet with Mg mass %, O mass %, S mass %, and Mn mass % contained in the molten steel. After adjusting so as to satisfy the following formula (excluding the case where 0.4 to 5 mass% of Cr is included) , the adjusted molten steel is continuously cast, and the molten steel is heated at a temperature equal to or higher than the temperature at which the molten steel starts to solidify. to generate MgO in, moreover, after the MnS it is to produce a MgS before starting the deposition, to precipitate MnS around the MgS.
(Mg mass% −1.5 × O mass%) × (S mass%)> 1.2 × 10 ⁻⁶
And
(Mg mass% −1.5 × O mass%)> 1/200 × (Mn mass%)
Incidentally, Mg mass% Mg mass% contained in the molten steel, O wt% O wt% is contained in the molten steel, S wt% S% by weight contained in the molten steel, Mn mass% is contained in the molten steel It is Mn mass %.
This slab uses Mg oxide such as MgO, MgO.Al2O3, etc. as inoculation nuclei when the molten steel solidifies, so that the solidification structure of the slab is made uniform and equiaxed to prevent internal defects. be able to. In addition, MnS is precipitated around MgS during the solidification process to prevent the precipitation of fine MnS in the parent phase (the first solidification structure), thereby suppressing the refinement of crystal grains due to fine dispersion of MnS. Promotes grain growth.
Therefore, the magnetism (iron loss) of the steel material manufactured from this slab can be improved.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention.
FIG. 1 is an overall cross-sectional view of a continuous casting apparatus used in a continuous casting method for molten steel for non-oriented electrical steel sheets according to an embodiment of the present invention.
As shown in FIG. 1, the continuous casting apparatus 10 used for the continuous casting method of the molten steel for non-oriented electrical steel sheets which concerns on one embodiment of this invention uses Mg wire which is an example of the metal magnesium (Mg) material which is not shown in figure. A tundish 12 storing hot water of the added molten steel 11, an immersion nozzle 13 attached to the bottom of the tundish 12, and a mold 14 for pouring the molten steel 11 flowing downward through the immersion nozzle 13; 14, a support segment 15 provided with a cooling water nozzle (not shown), a pressing segment 17 for pressing the slab 16 in which the molten steel 11 forms a solidified shell 16 a, and a slab 16 for extracting the slab 16 at a predetermined speed. and a pair of pinch rolls 18.
[0009]
Next, the continuous casting method of the molten steel for non-oriented electrical steel sheets to which the continuous casting apparatus 10 is applied and the continuously cast slab for non-oriented electrical steel sheets will be described.
The molten steel 11 for the non-oriented electrical steel sheet is received in a ladle (not shown), sampled, O mass % and S mass % are measured, and based on this value, the metal Mg wire is added. After obtaining the Mg mass % in the molten steel 11 from the Mg yield and adjusting the Mg concentration ( mass %), S mass %, Mn mass %, and O mass % contained in the molten steel 11 to satisfy the following formula, this adjustment The molten steel 11 is continuously cast.
(Mg mass % −1.5 × O mass %) × (S mass %)> 1.2 × 10 ⁻⁶
And (Mg mass %-1.5 x O mass %)> 1/200 x (Mn mass %)
Incidentally, Mg mass% Mg mass% contained in the molten steel, O wt% O wt% is contained in the molten steel, S wt% S% by weight contained in the molten steel, Mn mass% is contained in the molten steel It is Mn mass %.
In the above formula, (1.5 × O mass %) is a value obtained from the stoichiometric calculation when all the oxygen in the molten steel becomes MgO, and the excessively added Mg mass % is ( (Mg mass % −1.5 × O mass %). In addition, as a result of experimentally determining the product of the excessively added Mg mass % and S mass %, it was found that MgS is stably generated if the product of concentration is greater than 1.2 × 10 ^−6. It was.
Furthermore, in order to generate MgS before MnS is generated (precipitation starts), the excess Mg mass % combined with S in the molten steel is set to be larger than 1/200 times the Mn mass % in the molten steel. Thereby, MgS is preferentially deposited over MnS.
[0010]
Molten steel 11 added with Mg and stored in the tundish 12 was poured into the mold 14 through an immersion nozzle 13 provided at the bottom of the tundish 12, cooled by the mold 14, and laid on the support segment 15. The solidified shell 16a is formed by cooling with water sprayed from the cooling water nozzle, and heat is removed by water spraying the cooling water as it goes downstream of the support segment 15.
The cast slab 16 whose thickness of the solidified shell 16a is sequentially increased by this heat removal is reduced by a pressing amount of 1 to 10 mm by the reduction segment 17 arranged on the downstream side of the support segment 15, and then completely solidified.
In the solidified slab 16, MgO or MgO · Al 2 O 3 is precipitated and formed at a temperature before the temperature of the molten steel 11 is lowered and before solidification is started, that is, a temperature higher than the temperature at which the molten steel 11 starts to solidify. In addition, since MgO and MgO.Al2O3 act as inoculation nuclei when the molten steel 11 is solidified, δ-iron precipitates around it to form uniform equiaxed crystals (solidified structure). be able to.
[0011]
Next, since Mg is added in a larger amount than the amount of Mg consumed for the reaction with O in the molten steel 11, the excessively added Mg is added to the molten steel 11 before the MnS starts to precipitate. Reacts with S (sulfur) to precipitate MgS.
The deposited MgS has a small difference between the lattice strain of MnS in the molten steel 11 (difference between the lattice constants of δ-Fe and MnS / the value of the lattice constant of δ-Fe), and the lattice matching between MgS and MnS is good. Therefore, the slab 16 is cooled in the continuous casting apparatus 10, and MnS is preferentially deposited around the MgS in a region where the temperature is about 1000 to 1200 ° C.
Thereby, it is possible to prevent fine MnS from being finely dispersed and precipitated in the matrix.
The non-oriented electrical steel sheet produced from this slab 16 precipitates finely dispersed MnS around MgS in advance, so that MnS dispersed in the slab 16 is reduced when heat-annealed, and pinning with fine MnS is performed. The action can be greatly suppressed, and the growth of crystal grains can be promoted. As a result, it is possible to cast the slab 16 in which the solidified structure is made uniform and equiaxed by the synergistic action of MgO and MgS, and the crystal grains are larger than in the case where fine dispersion precipitation of MnS is not suppressed.
This slab 16 is free from internal defects such as internal segregation occurring in the interior, center segregation due to molten steel flow, and center porosity, and eliminates care and scrapping of the slab 16 to improve the yield and quality of the good slab. be able to.
The slab 16 thus cast is pulled out by the pinch roll 18 and cut into a predetermined size by a cutting machine (not shown) and then conveyed to a subsequent process such as rolling.
Even in a non-oriented electrical steel sheet in which the slab 16 has been subjected to processing such as rolling, generation of internal defects and surface defects such as surface defects and wrinkles can be prevented, and the maintenance of the steel sheet and the improvement of good product yield can be prevented. Is possible.
Moreover, since a large amount of MnS is precipitated around MgS, it is possible to obtain excellent magnetism (low iron loss) because the extremely fine MnS suppresses the crystal grains in the slab 16 from being extremely refined. it can.
[0012]
The type and amount of inclusions in the slab 16 can be measured by cutting out a part of the entire cross section of the slab 16 and observing the cut piece with a commonly used optical microscope.
Further, the solidified structure can be determined by etching the slab 16 with picric acid to detect a dendrite structure and determining whether the structure is equiaxed or columnar.
[0013]
【Example】
Next, examples of cast slabs cast using the continuous casting method for molten steel for non-oriented electrical steel sheets according to an embodiment of the present invention will be described.
350 tons of molten steel for a non-oriented electrical steel sheet having the composition shown in Table 1 is placed in a ladle, and Mg wire is added to the molten steel to obtain Mg concentration, S mass %, Mn mass %, O in the molten steel. Each mass % was adjusted, and the casting was cast into a mold having an inner dimension of 250 mm in thickness and 1200 mm in width, and drawn by a pinch roll at a speed of 1.2 m / min to cast a slab. Then, the solidification structure and internal quality of the cast slab, the surface wrinkles and wrinkles of the steel sheet, and the magnetic properties were investigated. The results are shown in Table 2.
Examples 1 to 5 are cases where Mg mass %, S mass %, Mn mass %, and O mass % in the molten steel satisfy the relationship of the above-described formula of the present invention, and in each case, the solidified structure can be equiaxed. In addition, the internal quality is free of cracks, center segregation, center porosity, and other internal defects, and the non-oriented electrical steel sheet processed from this slab is free of surface flaws and wrinkles and has good magnetic properties. It was.
[0014]
[Table 1]

[0015]
[Table 2]

[0016]
On the other hand, Comparative Example 1 and Comparative Example 2 are cases where Mg was added to molten steel, but Mg mass %, S mass %, Mn mass %, and O mass % do not satisfy the relationship of the above-described formula of the present invention. In addition, MnS was precipitated earlier than MgS and MnS was finely dispersed, the growth of crystal grains was inhibited, the crystal grain size of the slab was reduced, and the magnetic properties were also poor.
Comparative Example 3 is a case where the added Mg was consumed by oxygen and MgS could not be generated. Fine MnS was dispersed and precipitated in the slab, and the crystal grain size of the slab was reduced, resulting in magnetic properties. Became defective.
Comparative Example 4 is a case where the addition amount of Mg is small, and Comparative Example 5 is a case where Mg is not added. In both cases, the solidified structure becomes columnar crystals, and all of internal defects, surface wrinkles / wrinkles, and magnetic properties are poor. became.
[0017]
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and all changes in conditions and the like that do not depart from the gist are within the scope of the present invention.
For example, the slab can be cast by a casting method such as an ingot casting method, a belt caster, or a roll in addition to continuous casting.
Furthermore, in addition to adding a wire that has been processed into a linear shape in which Mg, Mg alloy, or the like is covered with thin steel, Mg, Mg alloy, or the like can also be added by blowing it into molten steel using an immersion lance.
[0018]
【The invention's effect】
In the continuous casting method of the molten steel for non-oriented electrical steel sheets according to claim 1, Mg molten mass , O mass %, S mass %, and Mn mass % contained in the molten steel for molten steel for non-oriented electrical steel sheets. Since the adjusted molten steel is continuously cast after being adjusted to satisfy the predetermined range, the solidified structure of the slab solidified by the molten steel is made uniform and equiaxed to suppress internal defects, and care for the slab. It is possible to prevent scrapping and improve the yield of a good slab and improve the quality of the slab.
[0019]
In the cast piece for a non-oriented electrical steel sheet according to claim 2, Mg mass %, O mass %, S mass %, and Mn mass % contained in the molten steel for the non-oriented electrical steel sheet are within a predetermined range. After adjusting so as to satisfy, after continuously casting this adjusted molten steel, MgO is generated at a temperature equal to or higher than the temperature at which the molten steel starts to solidify, and MgS is generated before MnS starts to precipitate Since MnS is precipitated around MgS, it has uniform equiaxed crystals to prevent internal defects and surface flaws, etc., to increase the yield of products, and to precipitate MnS coarsely around MgS. The magnetic properties of the non-oriented electrical steel sheet can be stably improved.
[Brief description of the drawings]
FIG. 1 is an overall cross-sectional view of a continuous casting apparatus used in a continuous casting method for molten steel for non-oriented electrical steel sheets according to an embodiment of the present invention.
[Explanation of symbols]
10: continuous casting apparatus, 11: molten steel, 12: tundish, 13: immersion nozzle, 14: mold, 15: support segment, 16: slab, 16a: solidified shell, 17: reduction segment, 18: pinch roll

Claims

The molten steel for non-oriented electrical steel sheet is adjusted so that Mg mass %, O mass %, S mass %, and Mn mass % contained in the molten steel satisfy the following formula (provided that Cr is 0.4 to 5 mass) %)) , And then continuously casting the adjusted molten steel. A method for continuously casting molten steel for non-oriented electrical steel sheets.
(Mg mass % −1.5 × O mass %) × (S mass %)> 1.2 × 10 ⁻⁶
And (Mg mass %-1.5 x O mass %)> 1/200 x (Mn mass %)
Incidentally, Mg mass% Mg mass% contained in the molten steel, O wt% O wt% is contained in the molten steel, S wt% S% by weight contained in the molten steel, Mn mass% is contained in the molten steel It is Mn mass %.

The molten steel for non-oriented electrical steel sheet is adjusted so that Mg mass %, O mass %, S mass %, and Mn mass % contained in the molten steel satisfy the following formula (provided that Cr is 0.4 to 5 mass) %)) , And then continuously casting the adjusted molten steel, producing MgO in the molten steel at a temperature equal to or higher than the temperature at which the molten steel starts to solidify, and before the MnS starts to precipitate. After producing | generating this, MnS is precipitated around this MgS, The slab for non-oriented electrical steel sheets characterized by the above-mentioned.
(Mg mass % −1.5 × O mass %) × (S mass %)> 1.2 × 10 ⁻⁶
And (Mg mass %-1.5 x O mass %)> 1/200 x (Mn mass %)
Incidentally, Mg mass% Mg mass% contained in the molten steel, O wt% O wt% is contained in the molten steel, S wt% S% by weight contained in the molten steel, Mn mass% is contained in the molten steel It is Mn mass %.