JP4157255B2 - Annealing separator for grain-oriented electrical steel sheet and method for producing grain-oriented electrical steel sheet - Google Patents
Annealing separator for grain-oriented electrical steel sheet and method for producing grain-oriented electrical steel sheet Download PDFInfo
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- JP4157255B2 JP4157255B2 JP2000180364A JP2000180364A JP4157255B2 JP 4157255 B2 JP4157255 B2 JP 4157255B2 JP 2000180364 A JP2000180364 A JP 2000180364A JP 2000180364 A JP2000180364 A JP 2000180364A JP 4157255 B2 JP4157255 B2 JP 4157255B2
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
- H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
- H01F1/12—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials
- H01F1/14—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys
- H01F1/16—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys in the form of sheets
- H01F1/18—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys in the form of sheets with insulating coating
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Description
【0001】
【発明の属する技術分野】
本発明は方向性電磁鋼板の製造に際し、特にフォルステライト系絶縁被膜形成のための焼鈍分離剤を改良することによって、均一で優れた被膜特性を有し、かつ優れた磁気特性を有する方向性電磁鋼板を得ようとするものである。
【0002】
【従来の技術】
方向性電磁鋼板は、Si:2.5〜4.0%を含有する素材スラブを熱延し、焼鈍と1回または中間焼鈍を挟む2回以上の冷延により最終板厚とされる。次いで、連続焼鈍炉においてH2 あるいはN2 +H2 雰囲気中で脱炭焼鈍を行い、脱炭処理、一次再結晶処理、SiO2 を主成分とする酸化層形成処理を行う。その後、MgOを主成分とする焼鈍分離剤を鋼板に塗布し乾燥する。鋼板はコイル状に巻取られ、最終仕上げ焼鈍を行った後に、絶縁被膜剤処理とヒートフラットニング処理を行って最終製品となる。
【0003】
方向性電磁鋼板は圧延方向に<001>方位を持つGoss方位結晶粒が多数存在するために優れた磁気特性を有している。このGoss方位結晶粒は最終仕上げ焼鈍工程の二次再結晶過程で成長する。Goss方位結晶粒が優先的に成長するのは、鋼中にインヒビターとして分散している析出物(AlN,MnS等)によって、Goss方位以外の他方位結晶粒の成長が、Goss方位結晶粒成長開始温度域まで抑えられているからである。
従って優れた方向性電磁鋼板を製造するためには、鋼中のインヒビター(AlN,MnS等)の分散状態を適正に制御し、できるだけ正確な<001>方位を持つGoss方位結晶粒を成長させることが重要である。鋼中のインヒビターの分散状態はいろいろの要因により変化するが、特に最終仕上げ焼鈍時に形成されるフォルステライト被膜の形成状態が大きな影響を及ぼす。
【0004】
フォルステライト被膜は、脱炭焼鈍中に形成された酸化層中のSiO2 と、焼鈍分離剤中のMgOが、最終仕上げ焼鈍中に、SiO2 +2MgO→Mg2 SiO4 (フォルステライト)のとおりに反応して形成される。このフォルステライト被膜は鋼板の表面に形成されるため、鋼中のインヒビターと最終仕上げ焼鈍の雰囲気ガスとのやりとりを制御する重要な役割を持つ。
【0005】
フォルステライト被膜は仕上げ焼鈍途中の昇温過程およそ900℃あたりの温度域で形成されるが、その進行が遅れたり、あるいは形成された被膜が不均一またはポーラスな構造を呈したりした場合には、仕上げ焼鈍雰囲気からOやNが鋼中に過剰に侵入するため、鋼中のインヒビターが分解、粗大化または過剰化して適正なインヒビター分散状態を得られない。また、フォルステライト被膜形成反応が低温域から早めに進行しすぎた場合には、インヒビター構成元素が鋼中からフォルステライト被膜中へ過剰に吸上げられるため、鋼中のインヒビター不足が生じて適正なインヒビター分散状態を得られない。
【0006】
フォルステライト被膜形成反応の進行度やその形態には、鋼板表面酸化層中のSiO2 の量や形態、焼鈍分離剤中のMgO性状(純度、反応性、水和の進行度合、粒度、塗布量等)、および仕上げ焼鈍雰囲気ガス組成が大きく関係する。とりわけ焼鈍分離剤中のMgOの反応性は、フォルステライト被膜形成にとって非常に重要である。MgOの反応性が劣化すると、鋼板表面酸化層中のSiO2 と焼鈍分離剤中のMgOとの反応が進行し難くなり、フォルステライト被膜は形成され難くなる。MgOの反応性が良好であればSiO2 とMgOとの反応が進行し易くなり、フォルステライト被膜は形成され易くなる。
【0007】
MgO反応性はいろいろの要因によって変化するが、中でもMgO粒度の影響が大きい。MgO粒が大きい場合は、単位重量当りの表面積が小さくなり反応面積が減少するため、SiO2 とMgOとの反応が進行し難くなりMgO反応性は劣化する。また、被膜形成促進剤等を添加した場合でもMgO粒が大きいため、ミクロ的には促進剤濃度が不均一となり、局所的に促進剤濃度が少ない部分ではMgO反応性が劣化して、均一で良好なフォルステライト被膜を得られない。一方、MgO粒が小さい場合は、単位重量当りの表面積が大きくなり反応面積が増大するためSiO2 とMgOとの反応が進行し易くなり、MgO反応性が向上すると共に被膜形成促進剤等も均一分散するため、均一良好なフォルステライト被膜を得ることができる。
【0008】
通常、MgOを主成分とする焼鈍分離剤は、まず水と混合してスラリー状とし、次に溝付きロールなどを用いて鋼板へ塗布される。その後水分除去のため乾燥工程を経て、鋼板はコイル状に巻取られ、最終仕上げ焼鈍が施される。良好なフォルステライト被膜を得るためにはMgOスラリーを鋼板表面へ均一に塗布しなくてはならないが、MgO粒度はこのMgOスラリーの塗布性にも大きな影響を及ぼす。すなわち、MgO粒が小さい場合は、鋼板へ均一に塗布され易く乾燥後の鋼板との密着性も良く、フォルステライト被膜形成状態は良好である。一方、MgO粒が大きい場合は、均一塗布性が悪化して乾燥中に剥離が発生する場合があり、フォルステライト被膜形成状態は劣化する。
このようにMgO粒度は、MgO反応性とMgOスラリー塗布性に多大に関係しており、その結果、フォルステライト被膜形成状態を左右し、インヒビター分散状態、更には方向性電磁鋼板の磁性に大きな影響を及ぼす。
【0009】
MgO粒度に関する研究は過去より数多くなされてきている。例えば特開平5−239664号公報では、スラリー調整から鋼板塗布までの過程で超微細粉砕装置により微粒化を行う方法が開示されている。この機械的な方法によってMgO粒は超微細となり、MgO粒全体の表面積が増大するためMgO反応性は向上し、鋼板表面の均一塗布性も確保できる。しかし、MgO粒が小さすぎるために、MgOスラリー中の粒子が過剰に凝集し易くなるという問題が発生した。その結果、超微細粉砕機の狭い間隔が閉塞する危険性が発生し、また、場合によってはMgO粒が凝集しすぎて逆にかなり粗大化し、結局はMgO粒が大きい場合と同様に、MgO反応性とMgOスラリー塗布性が劣化するトラブルも発生した。
【0010】
特開平10−88242号公報では、MgO粉を水と混合してスラリー状にした際のMgO粒凝集特性を、横軸に攪拌速度、縦軸に累積90%径を示したグラフ中のある領域で規定する方法が提案されている。この方法は、MgO粉をMgOスラリーにした際に起こる「凝集」を適正範囲に制御することで、均一で優れた被膜特性を有するフォルステライト被膜を形成する条件を得ている。しかし、操業条件が縦軸、横軸のそれぞれの規定範囲を外れても不可である厳しいものとなることから、従来よりも正確な操業技術が必要となり、規定範囲を外れるものは使用不可のため廃棄しなくてはならず、多様なトラブル等が発生する工場現場操業の面で不利であった。
【0011】
【発明が解決しようとする課題】
上述したとおり、従来の技術では、MgOの粒度やMgO粒のスラリー中での凝集を制御することで良好なフォルステライト被膜を得る方法があっても、製造現場における操業性が困難になると共に、規定条件を外れたものは優れた被膜特性を得られないという不利な面があった。従って、操業、設備条件を細かく規定しなくともMgOの粒度を簡単に制御でき、かつ良好なフォルステライト被膜を得られる方法の開発が望まれていた。
【0012】
これらの問題を解決するために、本発明は「MgO粒がスラリー中で凝集してMgO粒が大きくなる」性質を十分に考慮した上で、「MgO粒がスラリー中で凝集した場合でも、鋼板に塗布、乾燥後のMgO粒は小さくなる」方法で、かつ現場操業に負荷のかからない方法を提供するものである。
【0013】
【課題を解決するための手段】
本発明者は、「MgO粒がスラリー中で凝集した場合でも、鋼板に塗布、乾燥後のMgO粒は小さくなる」方法を探究する際に、現場操業方法の変更または設備の改造により目的を達成するよりも、MgO粉そのものに目的を達成する性質を持たせれば、製造現場条件を特に変更させることなく容易に扱うことができると考えた。
そこでMgO粉の性質として、「スラリーにする前のMgO粒径>鋼板に塗布、乾燥後のMgO粒径」で示されるMgO粉であれば、「スラリー中で凝集後のMgO粒径>スラリーにする前のMgO粒径」であるから、「スラリー中で凝集後のMgO粒径>鋼板に塗布、乾燥後のMgO粒径」となり、目的の「MgO粒がスラリー中で凝集した場合でも、鋼板に塗布、乾燥後のMgO粒は小さくなる」方法を実現できる。
【0014】
すなわち、Si:2.5〜4.0%を含有する素材スラブを熱延し、焼鈍と1回または中間焼鈍を挟む2回以上の冷延により最終板厚とした後、次いで連続焼鈍炉においてH2 あるいはN2 +H2 雰囲気中で脱炭焼鈍を行い、その後、MgOを主成分とする焼鈍分離剤をスラリー状にして鋼板に塗布、乾燥し、コイル状に巻取り、最終仕上げ焼鈍を行う一連の工程からなる方向性電磁鋼板の製造方法において、この方法によって製造される方向性電磁鋼板に適用されるMgOを主成分とする焼鈍分離剤であって、鋼板に塗布、乾燥後の焼鈍分離剤の90%径が、スラリー状にする前の焼鈍分離剤の90%径より小さくなるものを用いることにより、本発明の課題を解決できる。
【0015】
上記工程でのスラリーの乾燥は、スラリーを鋼板に塗布後、500〜900℃の範囲に加熱された焼鈍炉中にて3〜40秒間の範囲内で保持して行うのが望ましく、乾燥炉内の雰囲気としては、大気でもN2 などの無酸素雰囲気でも良い。
【0016】
またMgO粉としては、Mgを含有する物質を1500℃以上で焼成してMgOを得る処理を施したものがとりわけ有利に適合する。ここでMgを含有する物質とは、MgCl2 、炭酸マグネシウム、塩基性炭酸マグネシウム、海水、苦汁、岩塩などであり、Mg(OH)2 でもかまわない。Mgを含有する物質を1500℃以上で焼成してMgOを得る具体的な処理方法としては、「アーマンリアクター」方式が知られており、この方法は、MgCl2 を主成分とする濃い海水を約2000℃付近で焼成してMgOを得るものである。
【0017】
スラリー前の90%径としては、100μm以下であるものが好ましい。ここで90%径とは、小粒径のものから数えて90%目のMgO粒の径である。
90%径の測定方式としては、レーザー回折式粒度分布測定装置を用いる。本発明においては、HORIBA製のLA−500を使用し、測定条件の選択は、分散液として室温の蒸留水を使用、攪拌方法として最高回転数1000rpm の8段階調節の4番目選択、循環方法として最大吐出量600ml/minの7段階調節の3番目選択、超音波分散バス使用なし、必要試料量は装置表示の適性範囲内とした。
【0018】
粒度測定用のMgO粉サンプルの採取方法としては、スラリー前のMgO粉は、MgO粉の入った紙袋やフレコンパックから任意に取り出した。鋼板に塗布、乾燥後のMgO粉は、実際の製品コイルにおいては、乾燥後の鋼板表面の幅方向全体から乾燥終了後10分間以内に、測定に必要な量を機械的に掻き集めた。
ここで実際の製品コイルを用いる以外に、実験室的には以下のようにして本発明効果を確認することができる。
【0019】
まず重量100gのMgO粉を、MgO粉の入った紙袋やフレコンパックから任意に取り出す。次に、0〜5℃の範囲に冷却された750cm3 の水中へ先の重量100gのMgO粉を投入し、約1000rpm の攪拌速度で攪拌してMgOスラリーを作製する。その後、鉄を主成分とする約0.3mm板厚の鋼板の両面にMgOスラリーを乾燥後、MgO粉重量が片面当り5g/m2 となるように塗布して、500℃に加熱された大気雰囲気の実験炉中で15秒間保持する。焼鈍後の鋼板温度は約300℃となり、塗布されたMgOスラリーは十分に乾燥した状態となる。この乾燥したMgO粉を、へら等を使用して鋼板表面から掻き落して粒度測定用のサンプルとする。
【0020】
このようにして得られた鋼板に、塗布、乾燥後のMgO粉と、紙袋やフレコンパックから任意に取り出したスラリー前のMgO粉の90%径を測定して比較を行う。なお、90%径の測定方式としては、レーザー回折式粒度分布測定装置を用い、詳細については先述のとおりである。測定の結果、塗布、乾燥後のMgO粉の90%径が、スラリー前のMgO粉の90%径より小さければ、本発明の効果が得られるMgO粉であると断定できる。
【0021】
【発明の実施の形態】
以下、この発明の解明経緯について述べる。
発明者らは、MgOについて、製造方法、粒度を種々に変更させたものを用いて、かかるMgOが磁気特性、被膜特性に及ぼす影響を調査した。その結果、アーマンリアクター方式により生成したMgOであって、鋼板に塗布、乾燥後の焼鈍分離剤の90%径が、スラリー状にする前の焼鈍分離剤の90%径より小さい場合に、磁気特性、被膜特性が向上することを新規に見出したのである。
すなわち本発明のMgOは、「スラリーにする前のMgO粒径>鋼板に塗布、乾燥後のMgO粒径」であるために、磁気特性、被膜特性が向上するのである。
【0022】
ここでアーマンリアクター方式と、従来方式であるロータリーキルン方式、マッフル炉方式との相違点を説明する。
アーマンリアクター方式ではMgO製造時に生石灰(CaO)を添加しないが、ロータリーキルン方式、マッフル炉方式では生石灰を添加する。従ってアーマンリアクター方式で製造されたMgOは、ロータリーキルン方式、マッフル炉方式で製造されたMgOよりもCaO含有量が少ないことが特徴である。
次にアーマンリアクター方式の焼成温度は、ロータリーキルン方式、マッフル炉方式よりも高い。アーマンリアクター方式では1500℃以上の温度、平均的には約2000℃付近で焼成するのに対して、ロータリーキルン方式では800〜1000℃、マッフル炉方式では1000〜1200℃の温度で焼成する。
一般にロータリーキルン方式とは加熱された回転する炉中で焼成する方法であり、マッフル炉方式とは比較的小型の釜状焼鈍炉で適度に攪拌しながら焼成する方法である。
【0023】
本発明のMgOの特徴は次の通りである。
(1)鋼板に塗布、乾燥後の90%径が、スラリー状にする前の90%径より小さい。
(2)アーマンリアクター方式で製造されている。
(3)1500℃以上の温度(約2000℃付近)で焼成する。
(4)CaO含有量が少ない。
本発明のMgOの最大の特徴である、「鋼板に塗布、乾燥後の90%径が、スラリー状にする前の90%径より小さくなる」理由としては、上記の(2)〜 (4)が大きく関係していると考えられるが、実際に起こっている現象としては、従来のロータリーキルン方式、マッフル炉方式で約1000℃付近の焼成により製造されたMgOと異なり、鋼板に塗布後の乾燥段階で、MgO粒の亀裂が拡大または新たに発生して分割が進み、全体として粒度が細かくなっていると推定できる。
【0024】
次に本発明の限定理由を述べる。
まず本発明に適用されるMgOは、鋼板に塗布、乾燥後の焼鈍分離剤の90%径が、スラリー状にする前の焼鈍分離剤の90%径より小さいことが特徴である。鋼板に塗布、乾燥後の90%径がスラリー前より大きい場合は、過剰な凝集反応が発生していることを示し、すなわちMgO粒が凝集してかなり粗大化しているためにMgO反応性およびMgOスラリー塗布性が劣化するため良くない。
【0025】
スラリー前の焼鈍分離剤の90%径は3.4〜103.2μmであることが好ましい。スラリー前の90%径が103.2μmを超えるとMgOスラリー塗布性が劣化する。90%径の下限については、鋼板に塗布、乾燥後の90%径がスラリー前より小さい3.4μmであれば特に問題になることはない。この際、鋼板に塗布・乾燥後の90%径は3.2〜78.4μmとするのがよい。
【0026】
製造方法としては、Mgを含有する物質を1500℃以上で焼成してMgOを得る処理を施したものがとりわけ有利に適合し、望ましくは約2000℃付近で焼成したものが良い。この方式として、アーマンリアクター方式が知られている。1500℃未満の焼成温度ではスラリー中で凝集したMgO粒の乾燥段階での分割・細粒化が進み難くなり、本発明効果が得られない。高温で焼成するほど本発明効果は得られ易くなると考えているが、実際はMgO粉製造設備の耐久性から約2000℃付近が最適である。
【0027】
化学成分的には、CaOが0.3%以下であることが好ましい。アーマンリアクター方式で製造されたMgOは、ロータリーキルン方式、マッフル炉方式で製造されたMgOよりもCaO含有量が少ないことが特徴であり、これも本発明効果である乾燥後のMgO粒度を細かくすることに貢献していると推定している。またCaOが過剰に存在する場合には、フォルステライト被膜形成の進行が劣化する傾向にあるため良くない。以上からCaO含有量の上限は、アーマンリアクター方式で通常生産される成分範囲の上限と等しく0.3%とした。
【0028】
MgOスラリーの乾燥方法としては、スラリーを鋼板に塗布後、500〜900℃の範囲に加熱された焼鈍炉中にて、3〜40秒間の範囲内で保持する方法が好ましい。この範囲を外れる乾燥方法では、本発明の効果を最大限に得ることができず、更に水分を十分に除去できなかったり、鋼板が過酸化を起こしたりしてフォルステライト被膜形成状態が劣化する。乾燥炉内の雰囲気としては、大気でもN2 などの無酸素雰囲気でも良いが、大気中である方がコスト面から費用は少なくて済む。
【0029】
本発明のMgOに、本発明効果が得られる範囲内で、本発明以外のMgOやその他の粉体を混合させても同様の本発明効果を得ることができる。その他の粉体としては、TiO2 粉末、Sb化合物、B化合物、Cl化合物などがある。
【0030】
【実施例】
[実施例1]
C:0.05%、Si:3%、Mn:0.06%、S:0.03%、N:0.005%、Cu:0.2%を含有し、残部が不可避的不純物とFeからなる0.30mmの板厚の鋼板を脱炭焼鈍して、表1に示すMgO粉を純水と混合してスラリー状にしたものを片面当り5g/m2 塗布し、800℃に加熱された炉中で大気雰囲気中10秒間乾燥させてコイル状に巻き取り、1150℃×20hrの最終仕上げ焼鈍を施して、ヒートフラットニング処理を行い製品とした。
【0031】
各製品から鋼板サンプルを採取して磁気特性を測定し、コイル全長の観察結果から被膜外観と不良部発生率を得た。また各コイルごとにMgOスラリー乾燥後のMgOサンプルを、乾燥させた鋼板表面の幅方向全体から乾燥終了後10分間以内に機械的に掻き集めて採取し、レーザー回折式粒度分布測定装置(HORIBA製のLA−500)により粒度分布を測定して90%径を求めた。結果を表2に示す。
本発明の範囲において磁気特性、被膜特性とも良好となっている。
【0032】
【表1】
【0033】
【表2】
【0034】
[実施例2]
C:0.06%、Si:3%、Mn:0.1%、S:0.03%、Al:0.03%、N:0.008%、Cu:0.2%を含有し、残部が不可避的不純物とFeからなる0.30mmの板厚の鋼板を脱炭焼鈍して、表1に示すMgO粉を純水と混合してスラリー状にしたものに、被膜形成促進剤としてTiO2 をMgO粉重量の3%加え、そのスラリーを片面当り5g/m2 塗布し、800℃に加熱された炉中で大気雰囲気中20秒間乾燥させてコイル状に巻き取り、1150℃×20hrの最終仕上げ焼鈍を施して、ヒートフラットニング処理を行い製品とした。
【0035】
各製品から鋼板サンプルを採取して磁気特性を測定し、コイル全長の観察結果から被膜外観と不良部発生率を得た。また各コイルごとでMgOスラリー乾燥後のMgOサンプルを、乾燥させた鋼板表面の幅方向全体から乾燥終了後10分間以内に機械的に掻き集めて採取し、レーザー回折式粒度分布測定装置(HORIBA製のLA−500)により粒度分布を測定して90%径を求めた。結果を表3に示す。本発明の範囲において磁気特性、被膜特性とも良好となっている。
【0036】
【表3】
【0037】
[実施例3]
C:0.08%、Si:3%、Mn:0.08%、S:0.03%、Al:0.03%、N:0.008%、Cu:0.1%、Sn:0.1%を含有し、残部が不可避的不純物とFeからなる0.23mmの板厚の鋼板を脱炭焼鈍して、表1に示すMgO粉を純水と混合してスラリー状にしたものに、被膜形成促進剤としてTiO2 をMgO粉重量の3%、Sb2 (SO4 )3 をMgO粉重量の0.2%加え、そのスラリーを片面当り6g/m2 塗布し、800℃に加熱された炉中で大気雰囲気中10秒間乾燥させてコイル状に巻き取り、1150℃×20hrの最終仕上げ焼鈍を施して、ヒートフラットニング処理を行い製品とした。
【0038】
各製品から鋼板サンプルを採取して磁気特性を測定し、コイル全長の観察結果から被膜外観と不良部発生率を得た。また各コイルごとでMgOスラリー乾燥後のMgOサンプルを、乾燥させた鋼板表面の幅方向全体から乾燥終了後10分間以内に機械的に掻き集めて採取し、レーザー回折式粒度分布測定装置(HORIBA製のLA−500)により粒度分布を測定して90%径を求めた。結果を表4に示す。本発明の範囲において磁気特性、被膜特性とも良好となっている。
【0039】
【表4】
【0040】
[実施例4]
表1に示すMgO粉を重量100gずつ採取して、それぞれを0〜5℃の範囲に冷却した750cm3 の水中へ投入し、約1000rpm の攪拌速度で攪拌してMgOスラリーを作製した。その後、Si:3%を含有した鉄を主成分とする0.3mm板厚の鋼板の両面に、MgOスラリーを乾燥後MgO粉重量が片面当り5g/m2 となるように塗布して、500℃に加熱した大気雰囲気の実験炉中で15秒間保持した。十分に乾燥したMgO粉をへらを使用して鋼板表面から掻き落し収集して、レーザー回折式粒度分布測定装置(HORIBA製のLA−500)により粒度分布を測定して90%径を求めた。結果を表5に示す。
上記のとおりの実験室的な方法によって、本発明のMgO粉は、塗布、乾燥後のMgO粉の90%径が、スラリー前のMgO粉の90%径より小さいことが確認できている。
実施例1〜3から、本発明のMgOを使用して方向性電磁鋼板を製造すれば、優れた磁気特性と被膜特性を得られることは明らかである。
【0041】
【表5】
【0042】
【発明の効果】
以上詳述したように、本発明のMgOを主成分とする焼鈍分離剤を使用して方向性電磁鋼板を製造すれば、極めて優れた磁気特性および被膜特性を有する方向性電磁鋼板を安定して製造することが可能となる。[0001]
BACKGROUND OF THE INVENTION
The present invention provides a directional electromagnetic steel having uniform and excellent coating characteristics and excellent magnetic properties by improving an annealing separator for forming a forsterite-based insulating coating, especially in the production of grain-oriented electrical steel sheets. A steel sheet is to be obtained.
[0002]
[Prior art]
The grain-oriented electrical steel sheet is made into a final sheet thickness by hot-rolling a material slab containing Si: 2.5 to 4.0% and cold-rolling at least twice with annealing and intermediate annealing. Next, decarburization annealing is performed in a continuous annealing furnace in an atmosphere of H 2 or N 2 + H 2 , and decarburization treatment, primary recrystallization treatment, and oxide layer formation treatment mainly containing SiO 2 are performed. Thereafter, an annealing separator mainly composed of MgO is applied to the steel sheet and dried. The steel sheet is wound into a coil shape, and after final finish annealing, it is subjected to an insulating coating agent treatment and a heat flattening treatment to obtain a final product.
[0003]
The grain-oriented electrical steel sheet has excellent magnetic properties because there are many Goss-oriented crystal grains having <001> orientation in the rolling direction. These Goss oriented grains grow in the secondary recrystallization process of the final finish annealing process. Goss-oriented crystal grains preferentially grow due to precipitates (AlN, MnS, etc.) dispersed as inhibitors in the steel. This is because the temperature is suppressed.
Therefore, in order to produce an excellent grain-oriented electrical steel sheet, the dispersion state of the inhibitors (AlN, MnS, etc.) in the steel is properly controlled, and Goss orientation crystal grains having the <001> orientation as accurate as possible are grown. is important. The dispersion state of the inhibitor in the steel varies depending on various factors, but the formation state of the forsterite film formed at the time of final finish annealing has a great influence.
[0004]
The forsterite coating is composed of SiO 2 in the oxide layer formed during decarburization annealing and MgO in the annealing separator in the final finish annealing as SiO 2 + 2MgO → Mg 2 SiO 4 (forsterite). Formed in reaction. Since this forsterite film is formed on the surface of the steel sheet, it has an important role in controlling the exchange between the inhibitor in the steel and the atmosphere gas of the final finish annealing.
[0005]
The forsterite film is formed in the temperature range of about 900 ° C. during the temperature raising process in the course of final annealing, but if the progress is delayed or the formed film exhibits a non-uniform or porous structure, Since O and N penetrate into the steel excessively from the finish annealing atmosphere, the inhibitor in the steel is decomposed, coarsened or excessive, and an appropriate inhibitor dispersion state cannot be obtained. In addition, when the forsterite film formation reaction proceeds too early from the low temperature range, the inhibitor constituent elements are excessively sucked from the steel into the forsterite film. Inhibitor dispersion cannot be obtained.
[0006]
The progress and form of the forsterite film formation reaction include the amount and form of SiO 2 in the oxidized surface layer of the steel sheet, the MgO properties in the annealing separator (purity, reactivity, progress of hydration, particle size, coating amount) Etc.), and finish annealing atmosphere gas composition is greatly related. In particular, the reactivity of MgO in the annealing separator is very important for forsterite film formation. When the reactivity of MgO is deteriorated, the reaction between SiO 2 in the oxidized surface layer of the steel sheet and MgO in the annealing separator becomes difficult to proceed, and a forsterite film is hardly formed. If the reactivity of MgO is good, the reaction between SiO 2 and MgO tends to proceed, and a forsterite film is likely to be formed.
[0007]
The MgO reactivity varies depending on various factors, but the influence of the MgO particle size is particularly great. If MgO grains is large, the surface area per unit weight is the reaction area decreases less, MgO reactivity becomes reaction between SiO 2 and MgO it is hardly proceeds is degraded. In addition, even when a film formation accelerator or the like is added, the MgO particles are large, so that the accelerator concentration is microscopically uneven, and the MgO reactivity is deteriorated at a portion where the accelerator concentration is locally low, and is uniform. A good forsterite film cannot be obtained. On the other hand, when the MgO particles are small, the surface area per unit weight is increased and the reaction area is increased, so that the reaction between SiO 2 and MgO is facilitated, the MgO reactivity is improved, and the film formation accelerator is uniform. Since it is dispersed, a uniform and excellent forsterite film can be obtained.
[0008]
Usually, an annealing separator containing MgO as a main component is first mixed with water to form a slurry, and then applied to a steel sheet using a grooved roll or the like. After that, a steel plate is wound into a coil shape through a drying process for removing moisture, and final finish annealing is performed. In order to obtain a good forsterite film, the MgO slurry must be uniformly applied to the surface of the steel sheet, but the MgO particle size greatly affects the applicability of the MgO slurry. That is, when the MgO grains are small, they are easily applied uniformly to the steel sheet and have good adhesion to the steel sheet after drying, and the forsterite film formation state is good. On the other hand, when the MgO grains are large, the uniform coatability is deteriorated and peeling may occur during drying, and the forsterite film forming state deteriorates.
As described above, the MgO particle size is greatly related to the MgO reactivity and the MgO slurry coating property. As a result, it influences the forsterite film formation state and has a great influence on the dispersed state of the inhibitor and also on the magnetic properties of the grain-oriented electrical steel sheet. Effect.
[0009]
Many studies on MgO particle size have been made since the past. For example, Japanese Patent Application Laid-Open No. 5-239664 discloses a method of atomizing with an ultrafine pulverizer in the process from slurry adjustment to steel plate application. By this mechanical method, the MgO grains become ultrafine and the surface area of the entire MgO grains increases, so that the MgO reactivity is improved and the uniform coating property on the steel sheet surface can be secured. However, since the MgO particles are too small, there is a problem that the particles in the MgO slurry are easily aggregated excessively. As a result, there is a risk that the narrow interval of the ultrafine pulverizer is clogged, and in some cases, the MgO particles are agglomerated too much and conversely become coarser, and eventually the MgO reaction is similar to the case where the MgO particles are large. And the trouble that MgO slurry application property deteriorates also occurred.
[0010]
Japanese Patent Laid-Open No. 10-88242 discloses a certain region in a graph in which MgO powder aggregation characteristics when mixing MgO powder with water to form a slurry, the stirring speed on the horizontal axis, and the cumulative 90% diameter on the vertical axis. The method specified in is proposed. In this method, conditions for forming a forsterite film having uniform and excellent film characteristics are obtained by controlling “aggregation” that occurs when MgO powder is made into an MgO slurry within an appropriate range. However, since the operating conditions are harsh, which is impossible even if the specified range of the vertical axis and the horizontal axis is out of range, more accurate operation technology is required than before, and those outside the specified range cannot be used. It was disadvantageous in terms of factory site operation that had to be disposed of and caused various troubles.
[0011]
[Problems to be solved by the invention]
As described above, in the conventional technology, even if there is a method for obtaining a good forsterite film by controlling the aggregation of MgO particles and MgO particles in the slurry, the operability at the manufacturing site becomes difficult, Those outside the specified conditions had the disadvantage that excellent film properties could not be obtained. Accordingly, it has been desired to develop a method capable of easily controlling the particle size of MgO and obtaining a good forsterite film without finely defining operation and equipment conditions.
[0012]
In order to solve these problems, the present invention considers the property that “MgO grains agglomerate in the slurry and the MgO grains become large”, and “the steel plate is It provides a method that makes the MgO grains smaller after coating and drying.
[0013]
[Means for Solving the Problems]
The present inventor achieved the purpose by changing the on-site operation method or remodeling equipment when exploring the method of “even when MgO grains agglomerate in the slurry, the MgO grains after application and drying on the steel sheet become smaller”. Rather than doing it, we thought that if the MgO powder itself has the property of achieving the purpose, it can be easily handled without changing the production site conditions.
Therefore, as the properties of MgO powder, if the MgO powder is represented by “MgO particle size before slurrying> MgO particle size applied to steel sheet and dried,” “MgO particle size after aggregation in slurry> slurry” “MgO particle size after agglomeration in slurry> MgO particle size after coating and drying on steel plate”, and even if the desired “MgO particles agglomerate in the slurry” The MgO grains after application and drying become smaller ”can be realized.
[0014]
That is, a material slab containing Si: 2.5 to 4.0% is hot-rolled to obtain a final sheet thickness by annealing and at least two cold rollings sandwiching intermediate annealing, and then in a continuous annealing furnace. Decarburization annealing is performed in an H 2 or N 2 + H 2 atmosphere, and then an annealing separator mainly composed of MgO is applied to a steel sheet in a slurry form, dried, wound into a coil, and subjected to final finish annealing. In a method for producing a grain-oriented electrical steel sheet comprising a series of steps, an annealing separator mainly composed of MgO applied to the grain-oriented electrical steel sheet produced by this method, which is applied to the steel sheet and annealed after drying. The problem of the present invention can be solved by using a material in which the 90% diameter of the agent is smaller than the 90% diameter of the annealing separation agent before forming the slurry.
[0015]
Desirably, the slurry is dried in the above step by applying the slurry to a steel plate and holding it in an annealing furnace heated to a temperature in the range of 500 to 900 ° C. for 3 to 40 seconds. The atmosphere may be air or an oxygen-free atmosphere such as N 2 .
[0016]
Further, as the MgO powder, those obtained by firing Mg-containing material at 1500 ° C. or higher to obtain MgO are particularly suitable. Here, the substance containing Mg is MgCl 2 , magnesium carbonate, basic magnesium carbonate, seawater, bitter juice, rock salt, etc., and may be Mg (OH) 2 . As a specific processing method for obtaining MgO by baking a material containing Mg at 1500 ° C. or higher, an “Arman reactor” method is known. This method uses concentrated seawater mainly composed of MgCl 2. It is fired at around 2000 ° C. to obtain MgO.
[0017]
The 90% diameter before the slurry is preferably 100 μm or less. Here, the 90% diameter is the diameter of the 90% MgO particles counted from those having a small particle diameter.
As a 90% diameter measuring method, a laser diffraction particle size distribution measuring device is used. In the present invention, LA-500 manufactured by HORIBA is used, and selection of measurement conditions is performed by using distilled water at room temperature as a dispersion, fourth selection of eight-stage adjustment at a maximum rotation speed of 1000 rpm as a stirring method, and as a circulation method. A third selection of 7-step adjustment with a maximum discharge amount of 600 ml / min, no use of an ultrasonic dispersion bath, and the required sample amount was within the appropriate range of the device display.
[0018]
As a method for collecting a MgO powder sample for particle size measurement, the MgO powder before slurry was arbitrarily taken out from a paper bag or flexible container pack containing the MgO powder. In an actual product coil, the MgO powder applied to the steel sheet and dried was mechanically scraped in an amount necessary for measurement within 10 minutes after the end of drying from the entire width direction of the steel sheet surface after drying.
Here, in addition to using an actual product coil, the effect of the present invention can be confirmed in the laboratory as follows.
[0019]
First, MgO powder having a weight of 100 g is arbitrarily taken out from a paper bag or flexible container pack containing MgO powder. Next, the MgO powder having a weight of 100 g is put into 750 cm 3 of water cooled to 0 to 5 ° C. and stirred at a stirring speed of about 1000 rpm to prepare an MgO slurry. Thereafter, the MgO slurry is dried on both sides of a steel sheet having a thickness of about 0.3 mm mainly composed of iron, and then applied so that the weight of MgO powder is 5 g / m 2 per side, and heated to 500 ° C. Hold for 15 seconds in an atmospheric laboratory furnace. The steel plate temperature after annealing is about 300 ° C., and the applied MgO slurry is in a sufficiently dry state. The dried MgO powder is scraped off from the steel sheet surface using a spatula or the like to obtain a sample for particle size measurement.
[0020]
A comparison is made by measuring the 90% diameter of the MgO powder after coating and drying, and the MgO powder before slurry arbitrarily taken out from a paper bag or flexible container pack, on the steel plate thus obtained. In addition, as a measuring method of a 90% diameter, a laser diffraction type particle size distribution measuring device is used, and details are as described above. As a result of the measurement, if the 90% diameter of the MgO powder after application and drying is smaller than the 90% diameter of the MgO powder before the slurry, it can be determined that the MgO powder can achieve the effects of the present invention.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the elucidation process of the present invention will be described.
The inventors investigated the influence of MgO on magnetic properties and film properties using various changes in the manufacturing method and particle size of MgO. As a result, when the 90% diameter of the annealing separator after being applied to the steel sheet and dried is smaller than the 90% diameter of the annealing separator before being made into a slurry, the magnetic properties are MgO produced by the Armor reactor method. Thus, it has been newly found that the film properties are improved.
That is, since the MgO of the present invention is “MgO particle size before slurrying> MgO particle size after coating and drying on steel plate”, the magnetic properties and coating properties are improved.
[0022]
Here, the difference between the Arman reactor method, the conventional rotary kiln method, and the muffle furnace method will be described.
In the Arman reactor method, quick lime (CaO) is not added during the production of MgO, but quick lime is added in the rotary kiln method and the muffle furnace method. Therefore, MgO produced by the Armor reactor system is characterized by a lower CaO content than MgO produced by the rotary kiln system and the muffle furnace system.
Next, the firing temperature of the Arman reactor method is higher than that of the rotary kiln method and the muffle furnace method. Firing is performed at a temperature of 1500 ° C. or higher in the Arman reactor system, and on average, around about 2000 ° C., whereas it is performed at a temperature of 800 to 1000 ° C. in the rotary kiln system and 1000 to 1200 ° C. in the muffle furnace system.
In general, the rotary kiln method is a method of firing in a heated rotating furnace, and the muffle furnace method is a method of firing with moderate stirring in a relatively small kettle-type annealing furnace.
[0023]
The characteristics of the MgO of the present invention are as follows.
(1) The 90% diameter after applying and drying on a steel sheet is smaller than the 90% diameter before making into a slurry.
(2) Manufactured with an armor reactor system.
(3) Firing at a temperature of 1500 ° C. or higher (about 2000 ° C.).
(4) Low CaO content.
The reason why “the 90% diameter after applying to a steel plate and drying is smaller than the 90% diameter before making into a slurry”, which is the greatest feature of MgO of the present invention, is the above (2) to (4). However, unlike the conventional rotary kiln method and muffle furnace method, which is produced by firing at about 1000 ° C., the phenomenon that actually occurs is the drying stage after application to the steel sheet. Thus, it can be estimated that the cracks of the MgO grains are enlarged or newly generated and the division proceeds and the particle size is fine as a whole.
[0024]
Next, the reasons for limiting the present invention will be described.
First, MgO applied to the present invention is characterized in that the 90% diameter of the annealing separator after coating and drying on the steel sheet is smaller than the 90% diameter of the annealing separator before forming a slurry. When the 90% diameter after application and drying on the steel plate is larger than that before the slurry, it indicates that excessive agglomeration reaction has occurred, that is, MgO particles are agglomerated and considerably coarsened, so MgO reactivity and MgO It is not good because the slurry coatability deteriorates.
[0025]
The 90% diameter of the annealing separator before the slurry is preferably 3.4 to 103.2 μm. If the 90% diameter before the slurry exceeds 103.2 μm, the MgO slurry coating property deteriorates. The lower limit of the 90% diameter, coating the steel sheet, the 90% size after drying is never particularly problematic if 3.4μm have less than the previous slurry. At this time, the 90% diameter after coating and drying on the steel plate is preferably 3.2 to 78.4 μm.
[0026]
As a production method, a material obtained by firing a material containing Mg at 1500 ° C. or higher to obtain MgO is particularly suitable, and desirably a material fired at about 2000 ° C. is preferable. As this method, the Armor reactor method is known . When the firing temperature is less than 1500 ° C., it becomes difficult for the MgO particles agglomerated in the slurry to be divided and refined in the drying stage, and the effects of the present invention cannot be obtained. Although it is considered that the effect of the present invention is more easily obtained by firing at a higher temperature, in practice, about 2000 ° C. is optimal in view of the durability of the MgO powder production facility.
[0027]
In terms of chemical component, CaO is preferably 0.3% or less. MgO produced by the Arman reactor system is characterized by a lower CaO content than MgO produced by the rotary kiln system and the muffle furnace system, and this is also the effect of the present invention to reduce the MgO particle size after drying. It is estimated that it contributes to. Further, when CaO is excessively present, the progress of forsterite film formation tends to deteriorate, which is not good. From the above, the upper limit of the CaO content was set to 0.3%, which is equal to the upper limit of the component range normally produced by the Armor reactor system.
[0028]
As a drying method of the MgO slurry, a method of holding the slurry in a range of 3 to 40 seconds in an annealing furnace heated to a range of 500 to 900 ° C. after applying the slurry to a steel plate is preferable. If the drying method is out of this range, the effect of the present invention cannot be obtained to the maximum, and further, water cannot be sufficiently removed, or the steel sheet is peroxidized, so that the forsterite film formation state deteriorates. The atmosphere in the drying furnace may be air or an oxygen-free atmosphere such as N 2, but the air is less expensive in terms of cost.
[0029]
The same effect of the present invention can be obtained by mixing MgO of the present invention with MgO other than the present invention and other powders within the range where the effect of the present invention is obtained. Other powders include TiO 2 powder, Sb compound, B compound, and Cl compound.
[0030]
【Example】
[Example 1]
C: 0.05%, Si: 3%, Mn: 0.06%, S: 0.03%, N: 0.005%, Cu: 0.2%, the balance being inevitable impurities and Fe A 0.30 mm-thick steel plate made of decarburized steel was decarburized and annealed, and the MgO powder shown in Table 1 mixed with pure water to form a slurry was applied at 5 g / m 2 per side and heated to 800 ° C. The product was dried in an air atmosphere for 10 seconds in an air atmosphere, wound into a coil, and subjected to a final finishing annealing of 1150 ° C. × 20 hr, and a heat flattening treatment was performed to obtain a product.
[0031]
A steel plate sample was collected from each product, the magnetic properties were measured, and the coating appearance and defective portion occurrence rate were obtained from the observation results of the entire coil length. In addition, the MgO sample after drying the MgO slurry for each coil is mechanically collected and collected within 10 minutes from the entire width direction of the dried steel sheet surface, and a laser diffraction particle size distribution measuring device (manufactured by HORIBA) The particle size distribution was measured by LA-500) to obtain a 90% diameter. The results are shown in Table 2.
Within the scope of the present invention, both magnetic properties and film properties are good.
[0032]
[Table 1]
[0033]
[Table 2]
[0034]
[Example 2]
C: 0.06%, Si: 3%, Mn: 0.1%, S: 0.03%, Al: 0.03%, N: 0.008%, Cu: 0.2%, A steel plate having a thickness of 0.30 mm, the balance of which is inevitable impurities and Fe, is decarburized and annealed, and MgO powder shown in Table 1 is mixed with pure water to form a slurry. 2 was added at 3% of the weight of MgO powder, the slurry was applied at 5 g / m 2 per side, dried in an air atmosphere for 20 seconds in a furnace heated to 800 ° C., wound up in a coil shape, 1150 ° C. × 20 hr. A final finish annealing was performed, and a heat flattening treatment was performed to obtain a product.
[0035]
A steel plate sample was collected from each product, the magnetic properties were measured, and the coating appearance and defective portion occurrence rate were obtained from the observation results of the entire coil length. In addition, the MgO sample after drying the MgO slurry for each coil is mechanically scraped and collected from the entire width direction of the dried steel sheet surface within 10 minutes after completion of the drying. The particle size distribution was measured by LA-500) to obtain a 90% diameter. The results are shown in Table 3. Within the scope of the present invention, both magnetic properties and film properties are good.
[0036]
[Table 3]
[0037]
[Example 3]
C: 0.08%, Si: 3%, Mn: 0.08%, S: 0.03%, Al: 0.03%, N: 0.008%, Cu: 0.1%, Sn: 0 A steel sheet having a thickness of 0.23 mm containing 1% and the balance of inevitable impurities and Fe is decarburized and annealed, and the MgO powder shown in Table 1 is mixed with pure water to form a slurry. As a film formation accelerator, TiO 2 is added to 3% of the weight of MgO powder, Sb 2 (SO 4 ) 3 is added to 0.2% of the weight of MgO powder, and the slurry is applied at 6 g / m 2 per side and heated to 800 ° C. The resulting product was dried in an air atmosphere for 10 seconds in an air atmosphere, wound into a coil, and subjected to a final finish annealing of 1150 ° C. × 20 hr, and a heat flattening treatment was performed to obtain a product.
[0038]
A steel plate sample was collected from each product, the magnetic properties were measured, and the coating appearance and defective portion occurrence rate were obtained from the observation results of the entire coil length. In addition, the MgO sample after drying the MgO slurry for each coil is mechanically scraped and collected from the entire width direction of the dried steel sheet surface within 10 minutes after completion of the drying. The particle size distribution was measured by LA-500) to obtain a 90% diameter. The results are shown in Table 4. Within the scope of the present invention, both magnetic properties and film properties are good.
[0039]
[Table 4]
[0040]
[Example 4]
100 g of MgO powder shown in Table 1 was sampled and put into 750 cm 3 of water cooled to a temperature of 0 to 5 ° C., and stirred at a stirring speed of about 1000 rpm to prepare a MgO slurry. Thereafter, MgO slurry was dried and applied to both surfaces of a 0.3 mm-thick steel plate mainly composed of iron containing Si: 3% so that the MgO powder weight was 5 g / m 2 per side. It was kept for 15 seconds in an experimental furnace in an air atmosphere heated to ° C. The sufficiently dried MgO powder was scraped off and collected from the steel plate surface using a spatula, and the particle size distribution was measured with a laser diffraction particle size distribution measuring device (LA-500 manufactured by HORIBA) to obtain a 90% diameter. The results are shown in Table 5.
It has been confirmed by the laboratory method as described above that the 90% diameter of the MgO powder after application and drying is smaller than the 90% diameter of the MgO powder before slurry.
From Examples 1 to 3, it is clear that excellent magnetic properties and coating properties can be obtained if grain oriented electrical steel sheets are produced using MgO of the present invention.
[0041]
[Table 5]
[0042]
【The invention's effect】
As described above in detail, if a grain-oriented electrical steel sheet is produced using the annealing separator mainly composed of MgO of the present invention, the grain-oriented electrical steel sheet having extremely excellent magnetic properties and coating properties can be stably obtained. It can be manufactured.
Claims (5)
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