JP3536306B2 - Method for producing oriented silicon steel sheet excellent in magnetic properties with few steel sheet flaws - Google Patents

Description

【発明の詳細な説明】 【０００１】 【産業上の利用分野】この発明は鋼板疵が少なくかつ磁
気特性の優れた方向性珪素鋼板の連続鋳造法による製造
方法である。 【０００２】 【従来の技術】方向性珪素鋼板は、主として変圧器その
他の電気機器の鉄芯材料として使用されるもので、磁束
密度、鉄損値等の磁気特性が優れていることが基本的に
重要である。近年、省資源、省エネルギーあるいは生活
環境悪化防止の観点から電気機器の鉄芯材料は、電力損
失低減・高効率化と共に低騒音化も求められている。 【０００３】方向性珪素鋼板の製造において特に重要な
工程は、いわゆる最終仕上焼鈍で一次再結晶粒から｛11
0 ｝〈001 〉方位の結晶粒に二次再結晶させることにあ
る。かような二次再結晶粒を効果的に促進させるために
は、一次再結晶粒の成長を抑制するインヒビターと称す
る分散相を必要とする。かかるインヒビターの代表的な
ものは、MnS 、MnSe、AlN およびVNのような硫化物や窒
化物等で、鋼中への溶解度が極めて小さい物質が用いら
れている。さらに、Sb、Sn、As、Pb、Ge、Cu、Mo等の粒
界偏析型元素もインヒビターとして利用されている。こ
れらのインヒビターの効果は最終仕上焼鈍前までに均
一、かつ適性なサイズにインヒビターを分散させること
によって達成される。このため、現状では、熱間圧延前
にスラブを高温加熱して、インヒビター元素を十分に固
溶させておき、熱延工程以降、二次再結晶までの工程で
析出分散状態を制御している。 【０００４】もう一つは、一回または二回以上の冷間圧
延および一回または二回以上の焼鈍によって得られた一
次再結晶粒組織が板厚方向全体にわたって適当な大きさ
の結晶粒で、かつ均一な大きさに分布させる。これらの
二つの条件を確保することが重要点であることは周知で
ある。ところで、近年の鉄鋼製造工程においては、スラ
ブの製造法が造塊・分塊法から連続鋳造法に大部分変わ
っている。かかる連続鋳造法を一方向性珪素鋼に単純に
適用した場合には、例えば、特開昭48−101317号公報に
開示されているごとく、連続鋳造法固有の急冷凝固によ
る柱状晶粒が前記スラブ加熱で異常成長を起こしやす
く、熱延後に粗大な延伸粒として残り、この粗大な延伸
粒が冷延・焼鈍を経た後も再結晶せずに残存し、最終仕
上げ焼鈍で｛110 ｝〈001 〉方位の二次再結晶が不完全
となる、いわゆる帯状細粒組織となり、磁気特性の劣化
を招くことが明らかになっている。 【０００５】また、連続鋳造スラブにはピンホール状の
欠陥や最終凝固位置である厚み中心部に偏析が生じるこ
ともよく知られている。これに対し、電磁的攪拌を付加
しながら連続鋳造した場合には帯状細粒起因の柱状晶が
減るが、負偏析のホワイトバンドが発生することも公知
である。しかも、ホワイトバンド周辺は逆にＣ、Si、
Ｓ、Se、Ｎ等の成分が中心部より顕著に偏析する。この
ため、インヒビターを固溶させるためのスラブ加熱条件
は当初成分設計したものよりはるかに高温・長時間が必
要となり、それによってスラブ粒も顕著に粗大化して帯
状細粒の発生を高める問題がある。一般的にスラブはガ
スまたは重油等による加熱法では比較的に低温（1250〜
1380℃）で長時間、電気的な加熱法では比較的高温（13
80〜1470℃）で短時間加熱される。 【０００６】近年、特殊鋼のスラブ加熱には高温・均
一加熱が容易であること、雰囲気制御が容易であるこ
と、熱効率が良いこと等から電気的な方法が採用され
だしている。ところが、連鋳スラブを融点に近い温度に
加熱した場合には、成分偏析による融点降下程度が把握
できていないため部分的に溶融し、それに伴って鋼板に
はヘゲ、穴あるいはふくれ等の欠陥を生じる問題があ
る。逆に、加熱温度を低めに設定した場合にはインヒビ
ターの固溶不足となり、二次再結晶不良を招く問題が生
じる。 【０００７】前記帯状細粒の防止方法として、特公昭54
−27820 号公報、特公昭50− 37009号公報にはそれぞれ
方向性珪素鋼板および高磁束密度珪素鋼板の製造方法に
おいて、連続鋳造したスラブから２回の熱延工程を経て
熱延板を造る技術を開示しているが、部分溶融に起因す
るヘゲ、穴およびふくれ欠陥については言及していな
い。 【０００８】特開平３−115529号公報ではスラブ加熱前
に１〜10％の圧下を加え、次いでスラブ粒の一部が溶融
する温度域まで加熱した後、1380〜1440℃で５〜60分保
持する方法を開示している。この技術では粒界偏析の一
部分を溶融するに止め、スラブ粒の粗大化抑制に効果的
であるが、工業的に部分的溶融にとどめる制御が困難な
場合がある。 【０００９】また、特公昭57−41526 号公報では電磁的
攪拌を付与しながら連続鋳造し、スラブ中心部の等軸晶
域を構成する結晶粒の95％以上を９mm² 未満に抑える技
術を開示している。この技術ではホワイトバンド近傍の
濃厚偏析の問題が未解決である。特公昭57−44734 号公
報ではホワイトバンドをスラブ表面からスラブ厚の１／
５以上中心側位置に発生させたスラブを用いる技術を開
示している。この技術ではホワイトバンドの発生位置を
単に中心部側に移動させたのみであり、濃厚偏析の問題
が残っている。 【００１０】さらに、特公昭58−43446 号公報ではやは
り連続鋳造時に電磁攪拌または超音波振動を付与し、柱
状晶の体積比を30〜70％に調整し、スラブ加熱温度に応
じた二次冷延率を適用する技術であり、前記開示技術と
同様に成分の濃厚偏析問題が未解決である。 【００１１】 【発明が解決しようとする課題】この発明は前記問題を
有利に解決しスラブ加熱時に起因するヘゲ、穴およびふ
くれ等の欠陥が少なく、かつ優れた磁気特性を有する方
向性珪素鋼板の製造方法を提案することを目的とする。 【００１２】 【課題を解決するための手段】本発明者らは連鋳スラブ
を素材とした実験において、磁気特性が良好であっても
ヘゲ、穴、ふくれのごとき欠陥が鋼板に頻発し、製品価
値がなくなる問題に遭遇した。この問題を鋭意解明した
結果、これら欠陥がスラブ中の濃厚な成分偏析やピンホ
ール状の内部欠陥の存在ならびにスラブ加熱条件と密接
な関係を有していることを思い出し本発明に到達した。 【００１３】すなわち、本発明は、含珪素鋼の溶鋼を連
続鋳造でスラブとし、そのスラブを加熱した後熱間圧延
を施し、その後１回または中間焼鈍を挟む２回以上の冷
間圧延を施して最終板厚に仕上げたのち、脱炭焼鈍を施
し、ついで鋼板表面に焼鈍分離剤を塗布してから仕上焼
鈍を施す一連の工程によって方向性珪素鋼板を製造する
に当たり、前記連続鋳造に際し、凝固進行中に電磁気的
攪拌の付与方向を５〜30秒間隔に交互に変えて鋳込み、
さらに1000℃以上でスラブに２〜20％の予歪を付与した
後1380℃以上1450℃以下に加熱することを特徴とする鋼
板疵の少ない磁気特性の優れた方向性珪素鋼板の製造方
法である。 【００１４】 【作用】次に、上記知見に至った実験結果について詳細
に説明する。Ｃ： 0.072％、Si：3.15％、Mn： 0.073
％、Se： 0.018％、Sb： 0.025％、Al： 0.026％及び
Ｎ：0.0080％を含む溶鋼を以下の条件で連続鋳造にてス
ラブとした。 【００１５】連続鋳造条件は付加的処置なしにそのま
ま鋳造、電磁的攪拌を一方向に付与しながら鋳造、
電磁的攪拌の付与方向を20秒ごとに変えて鋳造した３種
類とし、さらには、のスラブを1200℃で５％加工処
理を施したあと、徐冷却した。このように処理した215m
m 厚スラブから 200×200mm 試験片を切り出し、窒素雰
囲気中の小型誘導加熱炉で1340〜1480℃で30分間加熱
し、引続き熱間圧延により2.0mm 厚の熱延板とした後、
端部処理してから公知の冷間１回法で0.23mmの最終板厚
の製品に仕上げた。 【００１６】製品鋼板を評価するため、長さ２ｍごとの
ブロックに分けて鋼板の各種欠陥の有無を判定し、該当
する欠陥を有するブロック数を総ブロック数で割って百
倍したものを発生率と定義した。図１に連続鋳造条件及
び予備加工処理の有無と製品鋼板疵欠陥発生率の関係を
示す。図１から明らかなように連続鋳造に際して電磁的
攪拌の付与方向を交互に変えた場合にはヘゲ、穴及びふ
くれ欠陥を抑制する効果のあることがわかった。図２は
上述のスラブ加熱前のスラブの厚み方向につい
てサルファプリントと成分変化を調べた偏析状態の概念
図を示す。スラブの場合は最終凝固位置の中心部に顕
著な偏析が生じており、スラブの場合は表裏面から１
／４の位置にホワイトバンドが発生し、その内側に中心
偏析より著しい偏析が発生している。スラブの場合は
ホワイトバンドが消滅し、スラブでホワイトバンド位
置の内側に発生した濃厚偏析が軽減している。スラブ
の場合はスラブより若干偏析が軽減し、かつスラブ
に認められたピンホール等の鋳巣が消滅しているこ
とが判明した。予備加工処理したスラブは1200℃に保
持したことと、加工による歪が成分の拡散均一化を促進
させ、偏析が軽減すること、スラブ粒が細粒化するため
他のスラブより熱間強度が高くなったものと推定
される。 【００１７】以上の加熱前のスラブ材質調査と図１の結
果から、スラブ加熱温度が融点に近いため偏析が顕著な
部分では一部分が溶解し、一旦溶解すると容易に凝固せ
ず、強度低下し熱延中に微細な割れを生じ、鋼板表面に
通じた場合に大気酸化し、熱延中での割れが小さい場合
にはヘゲとなり、大きな場合には穴の発生に至ると考え
られる。一方、ふくれに関しては鋼中に固溶していたＮ
等のガス成分の一部分が高温あるいは高温溶融域でガス
化し、ピンホール等の内部欠陥を起点に加熱中に膨れる
ものと考えられる。したがって、インヒビターにAlN を
用いない鋼種ではふくれの発生は極めてまれである。 【００１８】ところで、溶融開始温度は一般に鋼を構成
する成分の種類及含有量で変化するが、特に鋼の組成が
炭化物窒化物等の析出物またはこれらの複合析出物を生
成する成分系では成分元素の種類及びその含有量のほ
か、鋳造後の熱履歴によっても析出物の析出状態が影響
を受けるため、部分溶融する温度は変化する。したがっ
て、スラブの溶融開始温度は一義的に決めることが困難
であり、例えば、ＣやSiを含有する場合はその含有量に
応じて溶融開始温度は次の通りに変化する。 【００１９】Ｃ：0.01％当り３／℃ Si： 0.1％当り 2.5／℃ ちなみに、前記図１に示した実験に供した鋼の成分系に
おける溶融開始温度を実験にて求めたところ、1453℃で
あった。一方、スラブ加熱温度を1380℃未満に下げた場
合には前述の鋼板欠陥は防止できるが、インヒビター成
分の固溶には60分以上の長時間を必要とし、電気的な加
熱法では経済的に不利となるので、1380〜1450℃範囲で
５〜60分の加熱が望ましい。 【００２０】次に、鋼板のふくれ欠陥に対するスラブ加
熱前の予備加工処理効果を明らかにするために、図１に
用いたものと同じ、電磁的攪拌の付与方向を変えて連続
鋳造したスラブを用い、再加熱温度と予備加工率を変え
て実験した。なお、スラブ加熱条件は1450℃、30分間行
い、以降の処理工程は図１で示した実験と同様に処理し
た。得られた結果を図３に示す。図３からふくれの発生
を抑制するためには1000℃以上の温度で、かつ２％以上
の予備加工処理が必要なことがわかった。ふくれ発生を
抑制するには加工温度1000℃以上、加工率２％以上が必
要な理由は明確でないが、ピンホール等の鋳巣を圧着す
るために上記条件であり、加工温度及び加工率が低すぎ
る場合は鋳巣等の欠陥を圧着するのに不十分なためと考
えられる。一方、20％超の加工率では、熱延率低下によ
り粗くなったスラブ組織の破壊・微細化効果が減るた
め、上限は20％に限定した。 【００２１】次に、成分偏析度に及ぼす電磁的攪拌方向
の電気的反転間隔の影響について検討した。図４はＣ：
0.070％、Si：3.20％、Mn：0.071 ％、Se：0.019 ％、
Sb：0.024 ％、Al： 0.026％及びＮ：0.0082％含有する
溶鋼を連続鋳造するに際し、電磁的攪拌を一方向または
２、３、５、10、20、30及び60秒間隔で反転して付与
し、対応スラブの厚み方向のＣ、Si成分調査を行い、偏
析指数（最大成分含有率と溶鋼成分含有率の比で定義）
を求めた結果を示す。高温加熱で溶融しないＣとSiの最
大偏析指数をそれぞれ1.2 及び1.04以下にするには電磁
的攪拌方向の電気的な切り替え間隔は５〜30秒が望まし
く、５秒未満の場合は電気的に切り替えても攪拌方向が
追随せず、不完全なために効果が小さいものと考えられ
る。また、切り替え間隔時間が長い場合には一方向の電
磁的攪拌に近づくためである。連続鋳造時の溶鋼攪拌す
る手段は電磁的攪拌のみならず、超音波振動等の攪拌も
有効であることは言うまでもない。 【００２２】以上に示した図１〜図４から、鋼板疵を防
いで方向性珪素鋼板を製造するには、次の、及び
に従う必要のあることが判明した。 連続鋳造に際して電磁的攪拌方向を５〜30秒間隔ご
とに変えて付与する。 1000〜1300℃で２〜20％の予備加工処理を施す。 インヒビター固溶のスラブ加熱は1380〜1450℃で行
う。望ましい加熱時間は５〜60分である。 【００２３】この発明の素材である含珪素鋼としては、
従来公知の成分組成のものいずれもが適合するが、代表
組成を掲げると次の通りである。 Ｃ： 0.025〜0.10wt％ Ｃは 0.025％未満では途中工程における結晶組織を均一
にする効果が少なく、一方0.10％より多いと脱炭焼鈍が
困難となり、磁気特性を劣化させるので、0.025 〜0.10
％の範囲内が望ましい。 【００２４】Si： 2.5〜4.0wt ％ Siは比抵抗を高め、渦流損を低下させるために必要であ
るが、2.5 ％未満では添加効果に乏しく、一方、4.0 ％
を越えると冷間圧延時に脆性割れを起こしやすくなるの
で、 2.5〜4.0 ％の範囲内が望ましい。Mn：Mnは熱間圧
延中の割れを防止するために0.03％以上を必要とする。
しかしながら0.12％を越えると磁気特性を劣化させるの
で、0.03〜0.12％の範囲内が望ましい。 【００２５】Ｓ、Se、Alのうちから選ばれる一種または
二種以上の合計が0.01〜0.15％ Ｓ、Se、Alはそれぞれ、インヒビターとして有効に機能
するが、単独使用又は併用のいずれであっても0.10％未
満では完全な二次再結晶粒が得られず、一方、0.15％を
越えると冷間圧延時に割れを起こし易くなるだけでな
く、仕上げ焼鈍でのＳ、Seの純化が不十分になる恐れが
あるので、 0.010〜0.15％の範囲内で添加することが望
ましい。 【００２６】インヒビターとしては上述したＳ、Se、Al
の他、Cu、Sn、MoおよびＰなども有利に適合するのでそ
れぞれ少量併せて含有させることもできる。ここに上記
成分の好適添加範囲はCu、Sn：0.01〜0.15％、Mo： 0.0
05％〜 0.1％、Ｐ：0.01〜0.2 ％であり、これらの各イ
ンヒビター成分についても、単独使用および複合使用い
ずれもが可能である。 【００２７】上記した成分条件を満たした溶鋼を連続鋳
造するに際し、電磁的攪拌の付与方向を５〜30秒間隔で
変え、偏析を軽減させることが重要である。得られたス
ラブは、通常スラブ加熱でインヒビターを固溶処理され
る。通常インヒビターの固溶処理には、1250℃以上で、
しかも比較的に低温では長時間保持し、高温では短時間
保持が利用されている。これに対してこの発明法ではス
ラブに２〜20％の圧下を加え、部分溶融起点となる偏析
を拡散で軽減させ、ふくれに起点となるピンホール等の
鋳巣を圧着させた後、高温の1380〜1450℃の範囲で望ま
しくは５〜60分電気的な加熱でインヒビターを固溶す
る。５〜60分の短時間加熱でインヒビターを固溶するに
は、1380℃が下限であり、1450℃を越えると部分的に液
体を生じ、鋼板疵を発生させるので上限を1450℃とし
た。 【００２８】この1380〜1450℃範囲への加熱には、密閉
構造にしやすく酸素濃度を下げられること、保護ガスに
よって酸化を防止できること、温度制御が可能であるこ
とおよび高温に効率よく加熱できること、等の理由か
ら、誘導加熱炉や抵抗加熱炉などの電気的加熱炉を用い
ることが有利である。また、スラブに２〜20％の予備加
工する際の1000℃以上望ましくは1300℃以下への加熱に
は、電気的加熱のみならず、低温加熱領域で経済的に有
利なガスまたは重油加熱炉等も適用できる。 【００２９】スラブ加熱でインヒビターを固溶処理後、
1.2〜4.0mm 厚の熱延鋼帯とする。熱延鋼帯を酸洗後、
１回の冷間圧延または中間焼鈍を挟む２回以上の冷間圧
延とそれに続く脱炭焼鈍、焼鈍分離剤塗布および仕上げ
焼鈍の工程は、公知の手段を用いることができる。 実施例１ Ｃ： 0.045％、Si：3.35％、Mn： 0.072％、Se： 0.019
％、Sb： 0.027％、Mo： 0.012％および残部不可避不純
物とFeよりなる溶鋼を 215mm厚スラブへの連続鋳造とス
ラブ加熱を行うに当たり、次の４条件で実施した。 【００３０】 Ａ：注入溶鋼を攪拌処理無しに連続鋳造を実施。 Ｂ：一方向の電磁攪拌を付与しながら連続鋳造を実施。 Ｃ：電磁的攪拌の付与方向を15秒間隔で交互に変えなが
ら連続鋳造を実施。 Ｄ：電磁的攪拌の付与方向を15秒間隔で交互に変えなが
ら連続鋳造し、1250℃再加熱後で10％の予備加工を実
施。 【００３１】該スラブを表１に示す条件でスラブ加熱
し、粗圧延機と仕上げ圧延機で 2.0mm厚の熱延板とし
た。ついで、1000℃、１分間の熱延板焼鈍とスケール除
去の酸洗を施し、一次冷延で0.60mm厚の中間板厚とし、
950℃、２分間の中間焼鈍を行い、二次冷延で0.23mm厚
の最終板厚とした。該コイルを湿水素中 820℃、２分間
の脱炭焼鈍を行い、MgO を主体とする焼鈍分離剤を塗布
した後、窒素雰囲気中 850℃、50時間の二次再結晶焼鈍
と1180℃、５時間の純化焼鈍を行って方向性珪素鋼帯の
製品とした。該製品コイルを 100ｍごとのブロックに分
けて表面欠陥の有無を判定し、該当する欠陥を有するブ
ロックを総ブロック数で割って百倍して発生率を求め
た。さらに、該コイルの両端部からサンプルを切り出
し、磁気特性とマクロ組織を調査した。その結果を表１
に示す。 【００３２】 【表１】 【００３３】表１から明らかなように、本発明法にした
がって連続鋳造を行い、予備加工処理後にスラブ加熱を
実施することにより表面欠陥が少なく、磁気特性の優れ
た方向性珪素鋼板が製造できる。 実施例２ Ｃ： 0.072％、Si：3.15％、Mn： 0.072％、Se： 0.018
％、Al： 0.025％、Sb： 0.024％、Ｎ：0.0080％および
残部不可避不純物とFeよりなる溶鋼を 215mm厚スラブへ
の連続鋳造とスラブ加熱を行うに当たり、次の４条件で
実施した。 【００３４】 Ｅ：注入溶鋼を攪拌処理無しに連続鋳造を実施。 Ｆ：一方向の電磁攪拌を付与しながら連続鋳造を実施。 Ｇ：電磁的攪拌の付与方向を15秒間隔で交互に変えなが
ら連続鋳造を実施。 Ｈ：電磁的攪拌の付与方向を15秒間隔で交互に変えなが
ら連続鋳造し、1250℃再加熱後で５％の予備加工を実
施。 【００３５】該スラブを表２に示す条件でスラブ加熱
し、粗圧延機と仕上げ圧延機で 2.7mm厚の熱延板とし
た。ついで、熱延板スケール除去の酸洗を施し、一次冷
延で 1.8mm厚の中間板厚とし、1100℃２分間の中間焼鈍
を行い、二次冷延で0.30mm厚の最終板厚とした。該コイ
ルを湿水素中 840℃、２分間の脱炭焼鈍を行い、MgO を
主体とする焼鈍分離剤を塗布した後、水素雰囲気1200
℃、20時間の仕上げ焼鈍を行って方向性珪素鋼帯の製品
とした。該製品コイルを 100ｍごとのブロックに分けて
表面欠陥の有無を判定し、実施例１と同様の方法で発生
率を求めた。さらに、該コイルの両端部からサンプルを
切り出し、磁気特性とマクロ組織を調査した。その結果
を表２に示す。 【００３６】 【表２】 【００３７】表２から明らかなように、本発明法にした
がって連続鋳造と予備加工処理後にスラブ加熱を実施す
ることにより、インヒビターの複合添加においても、先
の実施例と同様に効果のあることがわかる。 実施例３ Ｃ： 0.075％、Si：3.20％、Mn： 0.069％、Se： 0.020
％、Al： 0.027％、Sb： 0.025％、Sn： 0.045％、Ｎ：
0.0082％および残部不可避不純物とFeよりなる溶鋼を 2
50mm厚スラブへの連続鋳造とスラブ加熱を行うに当た
り、次の３条件で実施した。 【００３８】 Ｉ：一方向の電磁攪拌を付与しながら連続鋳造を実施。 Ｊ：電磁的攪拌の付与方向を15秒間隔で交互に変えなが
ら連続鋳造を実施。 Ｋ：電磁的攪拌の付与方向を15秒間隔で交互に変えなが
ら連続鋳造し、1250℃℃再加熱後で20％の予備加工を実
施。 該スラブを表３に示す条件でスラブ加熱し、粗圧延機と
仕上げ圧延機で 1.6mm厚の熱延板とした。ついで、1200
℃、１分間の熱延板焼鈍とスケール除去の酸洗を施し、
冷間圧延で0.23mm厚の最終板厚に仕上げた。該コイルを
湿水素中 840℃、２分間の脱炭焼鈍を行い、MgO を主体
とする焼鈍分離剤を塗布した後、水素と窒素の混合雰囲
気1200℃、20時間の仕上げ焼鈍を行って方向性珪素鋼帯
の製品とした。該製品コイルを 100ｍごとのブロックに
分けて表面欠陥の有無を判定し、実施例１と同様の方法
で発生率を求めた。さらに、該コイルの両端部からサン
プルを切り出し、磁気特性マクロ組織を調査した。その
結果を表３に示す。 【００３９】 【表３】 【００４０】表３から明らかなように、本発明法にした
がって連続鋳造を行い、予備加工処理後にスラブ加熱を
実施することにより、冷延１回法においても実施例１と
同様の効果のあることがわかる。 実施例４ Ｃ： 0.035％、Si：3.05％、Mn： 0.073％、Ｓ： 0.019
％および残部不可避不純物とFeよりなる溶鋼を 250mm厚
スラブへの連続鋳造とスラブ加熱を行うに当たり、次の
２条件で実施した。 【００４１】Ｌ：電磁的攪拌の付与方向を７秒間隔で交
互に変えながら連続鋳造を実施。 Ｍ：電磁的攪拌の付与方向を７秒間隔で交互に変えなが
ら連続鋳造し、1250℃再加熱後で15％の予備加工を実
施。 該スラブを表４に示す条件でスラブ加熱し、粗圧延機と
仕上げ圧延機で 2.4mm厚の熱延板とし、500 ℃で巻き取
った。ついで、熱延板スケール除去の酸洗を施し、一次
冷延で0.80mm厚の中間板厚とし、950 ℃、２分間の中間
焼鈍を行い、二次冷延で0.35mm厚の最終板厚とした。該
コイルを湿水素中 820℃、３分間の脱炭焼鈍を行い、Mg
O を主体とする焼鈍分離剤を塗布した後、水素雰囲気12
00℃、５時間の仕上げ焼鈍を行って方向性珪素鋼帯の製
品とした。該製品コイルを 100ｍごとのブロックに分け
て表面欠陥の有無を判定し、実施例１との同様の方法で
発生率を求めた。さらに、該コイルの両端部からサンプ
ルを切り出し、磁気特性とマクロ組織を調査した。その
結果を表４に示す。 【００４２】 【表４】 【００４３】表４から明らかなように、本発明法にした
がって連続鋳造を行い、予備加工処理後にスラブ加熱を
実施することにより、製品厚みの厚い場合も同様に効果
のあることが分かる。 実施例５ Ｃ： 0.037〜0.042 ％、Si：3.23〜3.26％、Mn： 0.068
〜0.073 ％を含み、さらに表５に示すインヒビター成分
を含有し残部不可避不純物とFeよりなる溶鋼を電磁的攪
拌の付与方向を30秒間隔で交互に変えながら連続鋳造
し、215mm 厚スラブとした。該スラブをインヒビターを
固溶するスラブ加熱前に予め1200℃で５％の加工を施
し、1430℃、25分間保持して抽出し、その後3.0mm 厚の
熱延板とした。 【００４４】該熱延板に1000℃、１分間の熱延板焼鈍と
酸洗を施した後、一次冷延で0.80mm厚の中間板厚とし、
ついで 950℃で２分間の中間焼鈍を施し、二次冷延で0.
30mm厚の最終板厚に仕上げた。引続き、湿水素中で 820
℃、３分間の脱炭焼鈍を施した後、 MgOを主成分とする
焼鈍分離剤を塗布し、水素中1180℃、８時間の仕上げ焼
鈍を施して方向性珪素鋼板とした。該製品コイルを 100
ｍごとのブロックに分けて表面欠陥の有無を判定し、実
施例１と同様に発生率を求めた。併せて該コイルの先後
端部からサンプルを採取し、磁気特性と結晶組織を調査
した。その結果を表６に示す。 【００４５】 【表５】 【００４６】 【表６】【００４７】表６から明らかなように、本発明法にした
がって連続鋳造を行い、かつ予備加工処理後のスラブ加
熱を実施することにより、鋼板疵の発生を抑制でき、磁
気特性のよい方向性珪素鋼板が得られる。 【００４８】 【発明の効果】以上説明したようにこの発明は、含珪素
の溶鋼を連続鋳造に関して電磁的攪拌の付与方向を定時
間間隔に交互に変え、さらにインヒビターを固溶する前
のスラブに予備加工を施し、スラブの成分偏析を軽減
し、ピンホール等の内部欠陥を圧着して消滅させ、粗い
スラブ組織を微細化した後、スラブ加熱でインヒビター
を固溶するようにしたので、鋼板のヘゲ、穴およびふく
れ欠陥を防ぎ、帯状細粒も防止できることから、品質向
上に大きく寄与するものである。Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a grain-oriented silicon steel sheet having few flaws and excellent magnetic properties by continuous casting. 2. Description of the Related Art Grain-oriented silicon steel sheets are mainly used as iron core materials for transformers and other electric equipment, and basically have excellent magnetic properties such as magnetic flux density and iron loss value. Is important. In recent years, from the viewpoint of resource saving, energy saving, or prevention of deterioration of living environment, iron core materials for electrical equipment have been required to reduce power loss, increase efficiency, and reduce noise. [0003] A particularly important step in the production of grain-oriented silicon steel sheets is the so-called final finishing annealing, which is carried out by reducing primary recrystallized grains by 11%.
It is to recrystallize crystal grains of 0 0 <001> orientation. In order to effectively promote such secondary recrystallized grains, a dispersed phase called an inhibitor for suppressing the growth of primary recrystallized grains is required. Typical examples of such inhibitors are sulfides and nitrides such as MnS, MnSe, AlN and VN, and substances having extremely low solubility in steel are used. Further, grain boundary segregation elements such as Sb, Sn, As, Pb, Ge, Cu, and Mo are also used as inhibitors. The effect of these inhibitors is achieved by dispersing the inhibitors to a uniform and appropriate size prior to final finish annealing. For this reason, at present, the slab is heated to a high temperature before hot rolling, the inhibitor element is sufficiently dissolved, and the precipitation and dispersion state is controlled in the steps from the hot rolling step to the secondary recrystallization. . [0004] The other is that the primary recrystallized grain structure obtained by one or more cold rollings and one or more annealings is composed of appropriately sized grains throughout the thickness direction. , And a uniform size. It is well known that ensuring these two conditions is important. By the way, in the recent steel making process, the slab manufacturing method has largely changed from the ingot making / bulking method to the continuous casting method. When such a continuous casting method is simply applied to a unidirectional silicon steel, for example, as disclosed in JP-A-48-101317, columnar grains formed by rapid solidification inherent in the continuous casting method are used to form the slab. Abnormal growth is likely to occur by heating, and remains as coarsely stretched grains after hot rolling, and the coarsely stretched grains remain without recrystallization even after cold rolling and annealing, and in the final finish annealing, {110} <001> It has been clarified that secondary recrystallization of the orientation becomes incomplete, that is, a so-called band-like fine grain structure, which causes deterioration of magnetic properties. [0005] It is also well known that continuous casting slabs have pinhole-like defects and segregation at the center of the thickness which is the final solidification position. On the other hand, when continuous casting is performed while adding electromagnetic stirring, columnar crystals due to band-like fine grains are reduced, but it is also known that a white band of negative segregation is generated. Moreover, C, Si,
Components such as S, Se, and N segregate remarkably from the center. For this reason, the slab heating conditions for forming a solid solution of the inhibitor require much higher temperature and longer time than those originally designed, and there is a problem that the slab grains are remarkably coarsened and the generation of band-like fine grains is increased. . Generally, slabs are heated to relatively low temperatures (1250-
1380 ° C) for a long time and relatively high temperature (13
80-1470 ° C) for a short time. [0006] In recent years, electrical methods have been adopted for heating slabs of special steel due to the fact that high temperature and uniform heating are easy, the atmosphere is easily controlled, and the thermal efficiency is good. However, when the continuous cast slab is heated to a temperature close to the melting point, the molten steel is partially melted because the degree of melting point drop due to component segregation has not been grasped, and accordingly, the steel sheet has defects such as barbs, holes or blisters. There is a problem that causes. Conversely, if the heating temperature is set lower, the solution of the inhibitor will be insufficient, resulting in a problem of secondary recrystallization failure. [0007] As a method for preventing the above-mentioned band-like fine particles,
No. 27820 and Japanese Examined Patent Publication No. 50-37009 each disclose a technique for producing a hot rolled sheet from a continuously cast slab through two hot rolling steps in a method for producing a oriented silicon steel sheet and a high magnetic flux density silicon steel sheet. Although disclosed, no mention is made of barge, hole and blister defects due to partial melting. In JP-A-3-115529, a pressure of 1 to 10% is applied before heating the slab, and then the slab is heated to a temperature range in which a part of the slab grain is melted, and then kept at 1380 to 1440 ° C. for 5 to 60 minutes. A method for doing so is disclosed. Although this technique is effective in suppressing a part of the grain boundary segregation and suppressing the coarsening of the slab grain, it is sometimes difficult to control the slab grain to be partially melted industrially. [0009] Japanese Patent Publication No. 57-41526 discloses a technique in which continuous casting is performed while applying electromagnetic stirring to suppress 95% or more of the crystal grains constituting the equiaxed crystal region at the center of the slab to less than 9 mm ^2. are doing. This technique does not solve the problem of dense segregation near the white band. In Japanese Patent Publication No. 57-44734, a white band is set to 1 / th of the slab thickness from the slab surface.
A technique using a slab generated at 5 or more central positions is disclosed. In this technique, the position where the white band is generated is simply moved to the center, and the problem of dense segregation remains. In Japanese Patent Publication No. 58-43446, electromagnetic stirring or ultrasonic vibration is applied during continuous casting, the volume ratio of columnar crystals is adjusted to 30 to 70%, and secondary cooling is performed according to the slab heating temperature. This is a technique that uses elongation, and the problem of dense segregation of components is still unsolved as in the above-described disclosed technique. SUMMARY OF THE INVENTION The present invention advantageously solves the above-mentioned problems, and is a grain-oriented silicon steel sheet having few defects such as barbs, holes, and blisters caused by slab heating and having excellent magnetic properties. The purpose of the present invention is to propose a manufacturing method. Means for Solving the Problems In an experiment using a continuously cast slab as a material, the present inventors frequently found defects such as barbs, holes and blisters on a steel sheet, even if the magnetic properties were good. I encountered a problem where the product value was lost. As a result of elucidating this problem diligently, the present inventors have recalled that these defects have a close relationship with the presence of dense component segregation in the slab, the presence of pinhole-shaped internal defects, and the slab heating conditions, and have reached the present invention. That is, according to the present invention, a molten steel of silicon-containing steel is formed into a slab by continuous casting, and the slab is heated and then subjected to hot rolling, and then subjected to one or two or more cold rollings with intermediate annealing. After finishing to the final sheet thickness, decarburizing annealing is performed, and then a directional silicon steel sheet is manufactured by a series of steps of applying an annealing separating agent to the steel sheet surface and then performing finish annealing. During the casting, the direction of application of the electromagnetic stirring is alternately changed at intervals of 5 to 30 seconds and cast.
Further, a method for producing a grain-oriented silicon steel sheet excellent in magnetic properties with few steel sheet flaws, characterized in that a slab is given a pre-strain of 2 to 20% at 1000 ° C. or more and then heated to 1380 ° C. to 1450 ° C. . Next, the experimental results that led to the above findings will be described in detail. C: 0.072%, Si: 3.15%, Mn: 0.073
%, Se: 0.018%, Sb: 0.025%, Al: 0.026%, and N: 0.0080% were made into slabs by continuous casting under the following conditions. The continuous casting conditions include casting without any additional treatment, casting while applying electromagnetic stirring in one direction,
The slabs were subjected to 5% processing at 1200 ° C., and then gradually cooled after changing the direction of application of the electromagnetic stirring every 20 seconds. 215m treated in this way
A 200 x 200 mm test piece was cut out from a m-thick slab, heated in a small induction heating furnace in a nitrogen atmosphere at 1340-1480 ° C for 30 minutes, and subsequently hot-rolled into a 2.0 mm thick hot-rolled sheet.
After the end treatment, the product was finished to a final thickness of 0.23 mm by a known cold single process. In order to evaluate the product steel sheet, the presence or absence of various defects in the steel sheet is determined by dividing the steel sheet into blocks each having a length of 2 m, and the number of blocks having the corresponding defect is divided by the total number of blocks and multiplied by 100 to obtain the incidence rate. Defined. FIG. 1 shows the relationship between the continuous casting conditions, the presence or absence of pre-processing, and the incidence rate of defects in the product steel sheet. As is clear from FIG. 1, it was found that when the direction in which the electromagnetic stirring was applied was alternately changed during continuous casting, there was an effect of suppressing barge, hole and blister defects. FIG. 2 shows a conceptual diagram of a segregation state in which a sulfur print and a change in components in the thickness direction of the slab before the slab heating are examined. In the case of a slab, remarkable segregation has occurred at the center of the final solidification position.
A white band is generated at the position of / 4, and segregation more remarkable than center segregation is generated inside the white band. In the case of the slab, the white band disappears, and the dense segregation generated inside the white band position in the slab is reduced. In the case of the slab, it was found that segregation was slightly reduced as compared with the slab, and that the cavities such as pinholes observed in the slab had disappeared. Pre-processed slabs are maintained at 1200 ° C, and distortion due to processing promotes uniform diffusion of components, segregation is reduced, and hot strength is higher than other slabs because slab grains are refined. It is presumed that it has become. From the above investigation of the slab material before heating and the results shown in FIG. 1, the slab heating temperature is close to the melting point, and a portion where segregation is remarkable dissolves partly. It is considered that fine cracks are generated during rolling, and are oxidized in the atmosphere when they pass through the surface of the steel sheet. If the cracks during hot rolling are small, the cracks are formed, and if they are large, holes are generated. On the other hand, regarding blisters, N dissolved in steel
It is considered that a part of the gas components such as gasified at a high temperature or a high temperature melting region and swells during heating starting from internal defects such as pinholes. Therefore, blistering is extremely rare in steels that do not use AlN as an inhibitor. The melting start temperature generally varies depending on the type and content of the components constituting the steel. Particularly, in the case where the composition of the steel is such that the precipitates such as carbide nitrides or the composite precipitates thereof are formed, In addition to the type and content of the elements and the heat history after casting, the precipitation state of the precipitates is affected, so that the temperature at which partial melting is performed changes. Therefore, it is difficult to uniquely determine the melting start temperature of the slab. For example, when C or Si is contained, the melting start temperature changes as follows according to the content. C: 3 / .degree. C. per 0.01% Si: 2.5 / .degree. C. per 0.1% Incidentally, the melting start temperature in the steel component system used in the experiment shown in FIG. there were. On the other hand, if the slab heating temperature is lowered to less than 1380 ° C, the above-mentioned steel sheet defects can be prevented, but the solid solution of the inhibitor component requires a long time of 60 minutes or more, and the electric heating method is economical. Heating in the range of 1380 to 1450 ° C. for 5 to 60 minutes is desirable because it is disadvantageous. Next, in order to clarify the effect of the preliminary processing before slab heating on the blister defect of the steel sheet, the same slab as that used in FIG. The experiment was performed while changing the reheating temperature and the pre-processing rate. The slab was heated at 1450 ° C. for 30 minutes, and the subsequent processing steps were performed in the same manner as in the experiment shown in FIG. The results obtained are shown in FIG. From FIG. 3, it was found that in order to suppress the occurrence of blistering, a pre-processing at a temperature of 1000 ° C. or more and a processing of 2% or more was necessary. It is not clear why the processing temperature is 1000 ° C or more and the processing rate is 2% or more in order to suppress the occurrence of blistering. However, the above conditions are required for pressing the cavities such as pinholes, and the processing temperature and processing rate are low. If too large, it is considered that it is insufficient to press-bond defects such as cavities. On the other hand, if the working ratio exceeds 20%, the effect of breaking and refining the slab structure coarsened by the reduction of the hot rolling reduction decreases, so the upper limit is limited to 20%. Next, the effect of the electrical inversion interval of the electromagnetic stirring direction on the degree of component segregation was examined. FIG. 4 shows C:
0.070%, Si: 3.20%, Mn: 0.071%, Se: 0.019%,
When continuously casting molten steel containing Sb: 0.024%, Al: 0.026% and N: 0.0082%, electromagnetic stirring was applied in one direction or by inverting at intervals of 2, 3, 5, 10, 20, 30, and 60 seconds. Then, the C and Si components in the thickness direction of the corresponding slab are investigated, and the segregation index (defined by the ratio between the maximum component content and the molten steel component content)
Is shown. In order to reduce the maximum segregation index of C and Si which are not melted by high temperature heating to 1.2 or 1.04 or less, respectively, the electrical switching interval of the electromagnetic stirring direction is preferably 5 to 30 seconds, and if less than 5 seconds, the electrical switching is performed. However, it is considered that the effect is small because the stirring direction does not follow and is incomplete. Another reason is that when the switching interval time is long, it approaches one-way electromagnetic stirring. It is needless to say that not only electromagnetic stirring but also stirring such as ultrasonic vibration is effective as means for stirring molten steel during continuous casting. From FIG. 1 to FIG. 4 described above, it has been found that the following must be followed in order to manufacture a grain-oriented silicon steel sheet while preventing a steel sheet flaw. During continuous casting, the direction of electromagnetic stirring is changed at intervals of 5 to 30 seconds. Preliminary processing of 2-20% is performed at 1000-1300 ° C. The slab heating of the inhibitor solid solution is performed at 1380-1450 ° C. A desirable heating time is 5 to 60 minutes. The silicon-containing steel as the material of the present invention includes:
Although any of conventionally known component compositions are suitable, representative compositions are as follows. C: 0.025 to 0.10 wt% If C is less than 0.025%, the effect of making the crystal structure uniform in the middle of the process is small, while if it is more than 0.10%, decarburization annealing becomes difficult, and the magnetic properties deteriorate, so that 0.025 to 0.10%
% Is desirable. Si: 2.5-4.0 wt% Si is necessary to increase the specific resistance and reduce the eddy current loss, but if it is less than 2.5%, the effect of addition is poor, while 4.0%
If it exceeds 2,000, brittle cracking is likely to occur during cold rolling, so that the content is preferably in the range of 2.5 to 4.0%. Mn: Mn requires 0.03% or more to prevent cracking during hot rolling.
However, if it exceeds 0.12%, the magnetic properties deteriorate, so that the content is preferably in the range of 0.03 to 0.12%. The total of one or more selected from S, Se and Al is 0.01 to 0.15%. Each of S, Se and Al effectively functions as an inhibitor. If it is less than 0.10%, complete secondary recrystallized grains cannot be obtained. On the other hand, if it exceeds 0.15%, not only cracks are likely to occur at the time of cold rolling, but also S and Se are not sufficiently purified by finish annealing. Therefore, it is desirable to add within the range of 0.010 to 0.15%. The inhibitors described above include S, Se, and Al.
In addition, Cu, Sn, Mo, P and the like can be advantageously contained, so that they can be contained together in small amounts. Here, the preferred addition ranges of the above components are Cu, Sn: 0.01 to 0.15%, and Mo: 0.0
05% to 0.1%, P: 0.01 to 0.2%, and these inhibitor components can be used alone or in combination. In continuously casting molten steel satisfying the above-mentioned component conditions, it is important to change the direction of application of electromagnetic stirring at intervals of 5 to 30 seconds to reduce segregation. The obtained slab is usually subjected to solid solution treatment of the inhibitor by slab heating. Usually, for solid solution treatment of inhibitors, at 1250 ° C or higher,
In addition, holding is performed for a long time at a relatively low temperature, and is used for a short time at a high temperature. On the other hand, in the method of the present invention, a reduction of 2 to 20% is applied to the slab, segregation serving as a starting point of partial melting is reduced by diffusion, and a blowhole such as a pinhole serving as a starting point is press-bonded to a blister. The inhibitor is dissolved by electric heating in the range of 1380 to 1450 ° C, preferably for 5 to 60 minutes. In order to form a solid solution of the inhibitor by heating for a short time of 5 to 60 minutes, the lower limit is 1380 ° C., and if it exceeds 1450 ° C., a liquid is partially generated and a steel sheet flaw is generated. The heating to the temperature range of 1380 to 1450 ° C. includes the fact that it is easy to form a closed structure, the oxygen concentration can be reduced, the oxidation can be prevented by a protective gas, the temperature can be controlled, and the heating can be efficiently performed at high temperature. For this reason, it is advantageous to use an electric heating furnace such as an induction heating furnace or a resistance heating furnace. Heating to 1000 ° C or more and preferably 1300 ° C or less when pre-processing 2 to 20% of the slab is not only electric heating but also gas or heavy oil heating furnace which is economically advantageous in the low temperature heating area. Is also applicable. After the inhibitor is solid-solved by heating the slab,
Hot rolled steel strip of 1.2 to 4.0 mm thickness. After pickling the hot-rolled steel strip,
Known steps can be used for the steps of one or more cold rollings or two or more cold rollings sandwiching intermediate annealing, followed by decarburizing annealing, application of an annealing separator, and finish annealing. Example 1 C: 0.045%, Si: 3.35%, Mn: 0.072%, Se: 0.019
%, Sb: 0.027%, Mo: 0.012% and the balance of molten steel consisting of inevitable impurities and Fe into a 215 mm thick slab and slab heating were carried out under the following four conditions. A: Continuous casting of the poured molten steel was performed without stirring. B: Continuous casting was performed while applying magnetic stirring in one direction. C: Continuous casting was performed while alternately changing the application direction of the electromagnetic stirring at intervals of 15 seconds. D: Continuous casting was performed while alternately changing the direction of application of electromagnetic stirring at intervals of 15 seconds, followed by 10% preliminary processing after reheating at 1250 ° C. The slab was heated under the conditions shown in Table 1 to obtain a hot-rolled sheet having a thickness of 2.0 mm using a rough rolling mill and a finishing rolling mill. Then, hot rolled sheet annealing at 1000 ° C. for 1 minute and pickling for scale removal are performed, and the intermediate sheet thickness is 0.60 mm thick by primary cold rolling.
Intermediate annealing was performed at 950 ° C. for 2 minutes to obtain a final sheet thickness of 0.23 mm by secondary cold rolling. The coil was subjected to decarburizing annealing at 820 ° C. for 2 minutes in wet hydrogen, coated with an annealing separator mainly composed of MgO, and then subjected to secondary recrystallization annealing at 850 ° C. for 50 hours in a nitrogen atmosphere at 1180 ° C. and 5 ° C. The product was subjected to time annealing for purification to obtain a product of a directional silicon steel strip. The product coil was divided into blocks every 100 m to determine the presence or absence of a surface defect, and the block having the corresponding defect was divided by the total number of blocks and multiplied by 100 to determine the occurrence rate. Furthermore, samples were cut out from both ends of the coil, and the magnetic properties and macrostructure were investigated. Table 1 shows the results.
Shown in [Table 1] As is clear from Table 1, by performing continuous casting in accordance with the method of the present invention and performing slab heating after the preliminary processing, a grain-oriented silicon steel sheet having few surface defects and excellent magnetic properties can be manufactured. Example 2 C: 0.072%, Si: 3.15%, Mn: 0.072%, Se: 0.018
%, Al: 0.025%, Sb: 0.024%, N: 0.0080%, and the balance of molten steel consisting of unavoidable impurities and Fe were subjected to continuous casting to a 215 mm thick slab and heating of the slab under the following four conditions. E: Continuous casting of injected molten steel without stirring. F: Continuous casting was performed while applying unidirectional electromagnetic stirring. G: Continuous casting was performed while alternately changing the application direction of the electromagnetic stirring at intervals of 15 seconds. H: Continuous casting was performed while alternately changing the application direction of the electromagnetic stirring at intervals of 15 seconds, and 5% preliminary processing was performed after reheating at 1250 ° C. The slab was heated under the conditions shown in Table 2 to obtain a hot-rolled sheet having a thickness of 2.7 mm by a rough rolling mill and a finishing rolling mill. Then, pickling was performed to remove the scale of the hot-rolled sheet, the intermediate sheet thickness was 1.8 mm thick by primary cold rolling, the intermediate annealing was performed at 1100 ° C for 2 minutes, and the final sheet thickness was 0.30 mm thick by secondary cold rolling. . The coil was subjected to decarburizing annealing at 840 ° C. for 2 minutes in wet hydrogen, and after applying an annealing separator mainly composed of MgO, the coil was heated to a hydrogen atmosphere of 1200 ° C.
Finish annealing was performed at 20 ° C. for 20 hours to obtain a product of a directional silicon steel strip. The product coil was divided into blocks every 100 m to determine the presence or absence of surface defects, and the occurrence rate was determined in the same manner as in Example 1. Furthermore, samples were cut out from both ends of the coil, and the magnetic properties and macrostructure were investigated. Table 2 shows the results. [Table 2] As is evident from Table 2, by performing slab heating after continuous casting and pre-processing according to the method of the present invention, the same effect as in the previous example can be obtained in the case of the combined addition of inhibitors. Understand. Example 3 C: 0.075%, Si: 3.20%, Mn: 0.069%, Se: 0.020
%, Al: 0.027%, Sb: 0.025%, Sn: 0.045%, N:
0.0082% and the balance of molten steel consisting of unavoidable impurities and Fe
In performing continuous casting to a 50-mm thick slab and slab heating, the following three conditions were used. I: Continuous casting was performed while applying unidirectional electromagnetic stirring. J: Continuous casting was performed while alternately changing the application direction of the electromagnetic stirring at intervals of 15 seconds. K: Continuous casting was performed while alternately changing the direction of application of electromagnetic stirring at intervals of 15 seconds, followed by pre-processing of 20% after reheating at 1250 ° C. The slab was heated under the conditions shown in Table 3 to form a 1.6 mm thick hot rolled sheet by a rough rolling mill and a finishing rolling mill. Then 1200
℃ 1 minute hot rolled sheet annealing and pickling for scale removal,
Finished to a final thickness of 0.23 mm by cold rolling. The coil was subjected to decarburizing annealing at 840 ° C. for 2 minutes in wet hydrogen, coated with an annealing separator mainly composed of MgO, and then subjected to final annealing at 1200 ° C. for 20 hours in a mixed atmosphere of hydrogen and nitrogen for 20 hours. The product was a silicon steel strip. The product coil was divided into blocks every 100 m to determine the presence or absence of surface defects, and the occurrence rate was determined in the same manner as in Example 1. Further, samples were cut out from both ends of the coil, and the magnetic characteristics macrostructure was investigated. Table 3 shows the results. [Table 3] As is clear from Table 3, by performing continuous casting in accordance with the method of the present invention and performing slab heating after preliminary processing, the same effect as in Example 1 can be obtained even in the single cold rolling method. I understand. Example 4 C: 0.035%, Si: 3.05%, Mn: 0.073%, S: 0.019
% And the balance of inevitable impurities and Fe and molten steel were continuously cast into a 250 mm thick slab and slab heating was performed under the following two conditions. L: Continuous casting was performed while alternately changing the application direction of the electromagnetic stirring at intervals of 7 seconds. M: Continuous casting was performed while alternately changing the application direction of the electromagnetic stirring at intervals of 7 seconds, and a pre-processing of 15% was performed after reheating at 1250 ° C. The slab was heated under the conditions shown in Table 4 to form a 2.4 mm thick hot rolled sheet by a rough rolling mill and a finishing rolling mill, and was wound at 500 ° C. Next, pickling was performed to remove the scale of the hot-rolled sheet, the intermediate sheet thickness was 0.80 mm thick by primary cold rolling, intermediate annealing was performed at 950 ° C for 2 minutes, and the final sheet thickness was 0.35 mm thick by secondary cold rolling. did. The coil was subjected to decarburization annealing at 820 ° C for 3 minutes in wet hydrogen,
After applying an annealing separator mainly composed of O 2, a hydrogen atmosphere 12
Finish annealing was performed at 00 ° C. for 5 hours to obtain a product of a directional silicon steel strip. The product coil was divided into blocks every 100 m to determine the presence or absence of surface defects, and the occurrence rate was determined in the same manner as in Example 1. Furthermore, samples were cut out from both ends of the coil, and the magnetic properties and macrostructure were investigated. Table 4 shows the results. [Table 4] As is evident from Table 4, by performing continuous casting in accordance with the method of the present invention and performing slab heating after preliminary processing, the same effect can be obtained when the product thickness is large. Example 5 C: 0.037 to 0.042%, Si: 3.23 to 3.26%, Mn: 0.068
A slab of 215 mm thick was prepared by continuously casting molten steel containing 0.073%, containing the inhibitor components shown in Table 5, and comprising the balance of unavoidable impurities and Fe, alternately changing the application direction of electromagnetic stirring at intervals of 30 seconds. The slab was preliminarily subjected to 5% processing at 1200 ° C. before heating the slab for dissolving the inhibitor, and extracted at a temperature of 1430 ° C. for 25 minutes, and then a hot-rolled sheet having a thickness of 3.0 mm was obtained. After the hot-rolled sheet was subjected to hot-rolled sheet annealing at 1000 ° C. for 1 minute and pickling, an intermediate sheet thickness of 0.80 mm was obtained by primary cold rolling.
Then, it was subjected to intermediate annealing at 950 ° C for 2 minutes, and then subjected to secondary cold rolling at 0.
Finished to a final thickness of 30 mm. Subsequently, 820 in wet hydrogen
After decarburizing annealing at 3 ° C. for 3 minutes, an annealing separator containing MgO as a main component was applied, and finish annealing was performed at 1180 ° C. for 8 hours in hydrogen to obtain a grain-oriented silicon steel sheet. 100 coils of the product
The presence / absence of a surface defect was determined for each m blocks, and the occurrence rate was determined as in Example 1. At the same time, samples were taken from the front and rear ends of the coil, and the magnetic properties and crystal structure were investigated. Table 6 shows the results. [Table 5] [Table 6] As is apparent from Table 6, by performing continuous casting in accordance with the method of the present invention and performing slab heating after pre-processing, generation of flaws in the steel sheet can be suppressed, and directional silicon having good magnetic properties can be suppressed. A steel sheet is obtained. As described above, according to the present invention, the application direction of electromagnetic agitation is alternately changed at regular time intervals in continuous casting of molten steel containing silicon, and further, the slab before the inhibitor is solid-dissolved. Preliminary processing was applied to reduce the segregation of components in the slab, to eliminate internal defects such as pinholes by pressing, to refine the coarse slab structure, and then to dissolve the inhibitor by heating the slab. Since it can prevent bark, hole and blister defects, and can prevent band-like fine particles, it greatly contributes to quality improvement.

【図面の簡単な説明】 【図１】連続鋳造条件電磁攪拌付与の有無、および付与
方向、スラブ加熱温度と鋼板欠陥ヘゲ、穴およびふくれ
発生率の関係を示すグラフ。 【図２】連続鋳造条件とスラブ厚み方向の成分偏析を示
す概念図。 【図３】予備加工条件と鋼板欠陥・穴発生率の関係を示
すグラフ。 【図４】連続鋳造時の電磁攪拌付与方向の電気的反転時
間とＣおよびSiの最大偏析指数を示すグラフ。BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing the presence or absence of electromagnetic stirring under continuous casting conditions, the direction of application, the slab heating temperature, and the relationship between the rate of occurrence of barbed defects, holes, and blisters in a steel sheet. FIG. 2 is a conceptual diagram showing continuous casting conditions and component segregation in a slab thickness direction. FIG. 3 is a graph showing the relationship between pre-processing conditions and steel sheet defect / hole occurrence rates. FIG. 4 is a graph showing the electrical reversal time in the direction of applying electromagnetic stirring and the maximum segregation index of C and Si during continuous casting.

───────────────────────────────────────────────────── フロントページの続き (56)参考文献 特開 平３−115529（ＪＰ，Ａ) 特開 平３−243244（ＪＰ，Ａ) (58)調査した分野(Int.Cl.⁷，ＤＢ名) C21D 8/12 C21D 9/46 501 B21B 3/02 ────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-115529 (JP, A) JP-A-3-243244 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C21D 8/12 C21D 9/46 501 B21B 3/02

Claims (1)

(57)【特許請求の範囲】 【請求項１】 含珪素鋼の溶鋼を連続鋳造でスラブと
し、そのスラブを加熱した後熱間圧延を施し、その後１
回または中間焼鈍を挟む２回以上の冷間圧延を施して最
終板厚に仕上げたのち、脱炭焼鈍を施し、ついで鋼板表
面に焼鈍分離剤を塗布してから仕上焼鈍を施す一連の工
程によって方向性珪素鋼板を製造するに当たり、前記連
続鋳造に際し、凝固進行中に電磁気的攪拌の付与方向を
５〜30秒間隔に交互に変えて鋳込み、さらに1000℃以上
でスラブに２〜20％の予歪を付与した後1380℃以上1450
℃以下に加熱することを特徴とする鋼板疵の少ない磁気
特性の優れた方向性珪素鋼板の製造方法。(57) [Claims 1] A molten steel of silicon-containing steel is made into a slab by continuous casting, and the slab is heated and then subjected to hot rolling.
A series of steps of performing cold rolling two or more times with intermediate or intermediate annealing to finish to the final sheet thickness, performing decarburizing annealing, applying an annealing separator on the steel sheet surface, and then performing finish annealing In producing a grain-oriented silicon steel sheet, during the above-mentioned continuous casting, the direction of application of electromagnetic stirring is alternately changed at intervals of 5 to 30 seconds during solidification, and the slab is cast at a temperature of 1000 ° C. or higher by 2 to 20%. After applying strain 1380 ℃ or higher 1450
A method for producing a grain-oriented silicon steel sheet having excellent magnetic properties with less steel sheet flaws, characterized in that the steel sheet is heated to not more than ℃.