JP3644130B2 - Method for producing grain-oriented electrical steel sheet - Google Patents

Description

【００３９】
表１に示されるように、最も優れた磁気特性は、熱間圧延条件ａの鋼板で、熱延板焼鈍の昇温速度を12℃/sに制御し、中間焼鈍の均熱条件として1050℃で100 秒間とした場合に得られている。
【００４０】
ここで、こうした優れた結果を得た理由を調査するために、熱間圧延条件ａ，ｂ及びｃの熱延板について、それらを実験に合わせて昇温速度を３段階に変えて1000℃まで昇温してから急冷した鋼板について、鋼中の析出物の電子顕微鏡による観察結果を表２に示す。
【００４１】
【表２】

【００４２】
表２に示されているように、最も磁気特性の優れていた条件（熱間圧延条件ａ、熱延板焼鈍条件２，５，８（12℃/s) ）では、熱延板焼鈍の1000℃までの昇温過程で既に５〜10nmの微細なサイズのMnSe−AlN の複合析出物が極めて高密度に析出していることが分かる。この複合析出物は、熱延板の段階では認められないことから、熱延板焼鈍の昇温過程において生成したことは明らかである。この生成物の析出する密度は、その後の詳細な調査によって、熱間圧延の条件と熱延板焼鈍の600 〜800 ℃間における昇温速度に依存することがわかった。すなわち、熱延板焼鈍の600 〜800 ℃の間における昇温速度が５℃/s未満である場合には、析出核の析出頻度が低下し、析出物のサイズが増大しする。逆に昇温速度が30℃/sを超える場合は、微細、高密度に析出するのではあるが、均一な分散状態とはならない。また、別の調査によって、熱間圧延の条件としては、AlN が析出しない程度に低温であることが好ましく、つまり、低温での熱間圧延で導入される極微細な積層欠陥や析出物、介在物が、微細AlN の析出サイトになることがわかった。
【００４３】
ちなみに、Mn及びSeを含有するこの実験の場合、極めて微細なMnSeが熱間圧延の仕上圧延中に析出し、これが微細AlN の析出サイトとなって、５〜10nmの微細MnSe−AlN 複合析出物が生成したものである。なお、熱延板焼鈍の昇温途中に生成する微細AlN は、六方晶Wurtzite (ZnS)構造を有する結晶性析出物であり、熱延板焼鈍の昇温速度よっては多少のSiを有する場合もあるが、抑制力の作用に関しては粒径のみで定まるので、同等に取り扱ってよい。
【００４４】
上記熱間圧延において、かかるAlN の析出サイトを多数形成するのに、粗圧延開始から仕上圧延終了までの時間として450 秒間未満の熱間圧延時間で行う場合には、仕上圧延を従来より低温で行うのが良く、仕上圧延の開始温度を1000〜1230℃とし、終了温度を800 〜1100℃とすることが必要で、かような温度制御によって極めて微細な積層欠陥又は介在物あるいは析出物の生成頻度が増加し、熱延板焼鈍の昇温過程における微細AlN の析出サイトを提供できることになる。仕上圧延の温度が上記の温度より高い場合は微細AlN の析出サイトが不足し、表２の熱延条件ｃの欄に示されるように、熱延板焼鈍の昇温過程で新たに析出するAlN の頻度が低下し、かつサイズも増加して、インヒビターとしての良好な抑制力が得られない。
【００４５】
また、かかるAlN の析出サイトを確実に増加させるには、鋼中にＳ又は／及びSeを添加し、これらの極微細結晶物を熱間圧延において得ることが良い方法である。このためには、Ｓ及びSeの１種または２種を合計量で0.005 〜0.30％含有させて、硫化物及び／又はセレン化物を熱間圧延で形成させる。かかる析出物の極微細析出に適した熱間圧延条件は、仕上圧延開始温度として1000〜1200℃、終了温度として850 〜1000℃である。
【００４６】
もっとも、鋼中にSeを含有させる場合は、最も低温かつ長時間の熱間圧延によって、鋼中に極微細セレン化物を析出させることが可能であるので、熱間圧延の粗圧延開始から仕上圧延終了までの時間が450 秒間以上の特殊な熱間圧延においても、この発明を適用することが可能となる。
【００４７】
すなわち、鋼中にSeを0.005 〜0.030 ％含有させた鋼の熱間圧延においては、熱間圧延の仕上圧延開始から終了までの時間を460 秒以下とし、熱間圧延終了温度を850 〜1150℃とすることにより、熱延板焼鈍の昇温過程で析出する微細AlN の析出サイトとなる極微細セレン化物を高密度に析出させることができる。このとき、熱間圧延終了温度が1150℃を超えたり、仕上圧延開始から終了までの時間が460 秒を超えると、熱間圧延で析出するセレン化物が粗大なもののみとなり、逆に熱間圧延終了温度が850 ℃未満の場合は、極微細セレン化物の析出頻度が低下し、いずれの場合も熱延板焼鈍の昇温過程で析出する微細AlN が高密度の分布とならない。
【００４８】
次に、表２の熱延条件ａとｂとの差異について詳細に調査した結果を述べる。熱間圧延終了後の鋼板の冷却速度が遅い場合には、SiリッチのAlとSiとの複合窒化物（Si，Al）Ｎの安定析出状態となる。この複合窒化物は、結晶質の析出物（六方晶Wurtzite構造）であって熱的に比較的安定であり、表２に示した熱延条件ｂの熱延板中に認められるように粗大な析出物で、MnSeと複合析出物を形成したり、単独で花弁状析出物を生成している。この析出物は熱延板焼鈍の昇温過程でAlN （Siが鋼中に拡散し、逆にAlが侵入し、SiとAlが置換し、昇温条件にもよるが、Alリッチの（Al，Si）Ｎから最終的にAlN となる。）に変換するが、熱延板焼鈍後もそのサイズはほぼ維持される。
【００４９】
かかるSiリッチのAlとSiとの複合窒化物は、熱間圧延終了後のコイル巻き取り温度が高い場合にも認められ、熱延板焼鈍の昇温過程で析出する微細AlN の析出量と頻度を低下させるので、特に有害な析出物である。
【００５０】
ちなみに、熱間圧延終了後に急冷し、かつ低温度でコイル状に巻き取った表２の熱延条件ａやｃの熱延板中には、不定型（Si，Al）Ｎは認められても、結晶質の（Si，Al）Ｎはほとんど認められない。また、この不定型（Si，Al）Ｎは急冷に伴い生成した準安定なアモルファスであり、熱延板焼鈍の昇温過程の初期の段階で容易に分解、再固溶すると考えられるので、基本的にはこの窒化物は固溶状態にあるものと同一視して取り扱っても良い。
【００５１】
表２に示した熱延板及び熱延板昇温過程における1000℃昇温直後の鋼板での窒化物の析出量を測定し、析出程度を（窒化物としてのＮ）÷（トータルＮ）の値で算出評価すると、熱延条件ａの場合、熱延板で0.42、熱延板焼鈍1000℃昇温直後で、0.95であるのに対し、熱延条件ｂの場合では熱延板で0.84、熱延板焼鈍1000℃昇温直後で0.98であり、熱間圧延工程終了後で既に窒化物が大量に析出しており、熱延板焼鈍の昇温過程で新たに析出するAlN の量は極めて少ないことがわかる。
【００５２】
以上のように粗大かつ安定である理由で有害である結晶質の（Si，Al）Ｎの熱延板での析出を抑制するためには、熱間圧延終了後、700 ℃までの鋼板の冷却速度を10℃/s以上とすること、及びコイル巻き取り温度を650 ℃以下として、結晶質（Si，Al）Ｎの析出温度領域での長期滞留を避けることが必要である。
【００５３】
次に、この発明においては、熱延条件に関する第１の要件の他に、第２の要件として、熱延板焼鈍の昇温過程において生成した微細AlN を有効に活用するため、冷延圧延工程における焼鈍、すなわち熱延板焼鈍と、これに加えて２回の冷間圧延法においては、中間焼鈍を含めて焼鈍の最高温度を1125℃以下とすることが必要である。
【００５４】
実験では、表１の熱間圧延条件ａにおいて、かつ熱延板焼鈍の昇温速度が12℃/sの場合において、中間焼鈍の均熱温度が1050℃の場合には極めて優れた磁気特性の製品が得られたが、均熱温度を1150℃に高めると大幅な磁気特性の劣化が生じた。
【００５５】
この理由を探究するために、インヒビターの析出粒径分布の変化を調べ、抑制力についての調査を行った。図１は熱間圧延条件ａにおいて、熱延板焼鈍の昇温速度が12℃/sで、中間焼鈍条件が1050℃で100 秒間の場合、すなわち、この発明の方法に従う試料について、熱延板と熱延板焼鈍の1000℃昇温直後の鋼板及び脱炭・一次再結晶焼鈍後の析出物の粒径分布の測定結果を示している。一方、図２は、熱間圧延条件ｃにおいて、熱延板焼鈍の昇温速度が12℃/sで中間焼鈍条件が1150℃で60秒間の場合、すなわち、従来の方法における各鋼板の析出物の粒径分布の測定結果を示している。なお、ここで中間焼鈍後の鋼板には微細カーバイトが多数析出し、インヒビターである析出物との区別が困難であるので、図に示すのは省略してある。
【００５６】
図１に示されるように、この発明の方法では、熱延板焼鈍の1000℃までの昇温によって50〜100 Åのサイズの微細な析出物が多数析出し、この状態は脱炭・一次再結晶焼鈍後もほぼ変わらず維持されている。
【００５７】
これに対し、図２に示される従来の方法では、熱延板焼鈍によってもさほど微細析出物の量は増加しておらず、脱炭・一次再結晶焼鈍後の鋼板で初めて100 〜200 Åのサイズの微細析出物が増加している。この場合の微細析出物の析出時期と変化について、より詳細に調査したところ、一部は熱延板焼鈍の冷却時に析出し、中間焼鈍の高温時にα相中でオストワルド成長により、やや粗大化し、残りは中間焼鈍の高温時にγ相中で固溶し、冷却時に再析出しているものであった。このように、中間焼鈍でのオストワルド成長と固溶・再結晶過程とで、インヒビターの粒径分布が制御されるため、熱間圧延や熱延板焼鈍など、前工程の影響を受けることが少なく安定した粒径分布が得られる。
【００５８】
しかしながら、析出物のサイズとしては、この発明の方法に比べやや大きく、満足のいくサイズではない。これに対し、この発明の方法においては、熱間圧延条件及び熱延板焼鈍の条件を厳しく制御することで、50〜100 Åのサイズの極めて微細な析出物を得ることが可能となった。これは、極めて強い抑制力を有するインヒビターの析出制御が可能になったことを意味する。
【００５９】
さらに、この調査に引き続いて、前述の中間焼鈍温度1150℃での磁気特性劣化の原因を調査したところ、50〜100 Åの析出物がオストワルド成長により粗大化していることがわかり、また、かかるオストワルド成長を抑制するためには、中間焼鈍温度を1125℃以下に規制することが必要であることが分かった。
【００６０】
したがって、両者の方法において、種々の得失はあるが、熱間圧延条件及び熱延板焼鈍の昇温速度及び冷間圧延工程の最高温度規制に留意している限りにおいては、この発明の方法によって極めて優れた磁気特性の製品が得られる利点がある。
【００６１】
次に、この発明の第３の要件である集合組織の制御について述べる。
表１の熱間圧延条件ａにおいて、熱延板焼鈍の昇温速度12℃/sの欄において、中間焼鈍条件として均熱温度：1050℃、時間：60秒間と、100 秒間とを比較すると、100 秒間の処理のほうが、磁束密度、鉄損ともに際立って優れている。この原因について詳細に調査したところ、両者において、微細AlN の析出状態に大きな差異はなかったが、脱炭・一次再結晶集合組織を比較したところ、均熱時間：100 秒間の試料（ａ₅ ）は、均熱時間：60秒間の試料（ａ₂ ）に比較して、（１１０）〔００１〕粒の密度が約1.5 倍に増加し、｛１１１｝〈１１２〉粒の密度は逆に0.8 倍に低下していた。この（１１０）〔００１〕粒の増加は、より方位の優れた結晶粒が二次再結晶の核となる確率を高め、｛１１１｝〈１１２〉粒の密度の低下は、方位の劣る結晶粒が二次再結晶の核となるのを抑制するので、最終的に二次再結晶粒の方位を向上させるのに役立つ。
【００６２】
かかる脱炭・一次再結晶集合組織の変化をもたらした原因をさらに追求したとろ、中間焼鈍後の平均結晶粒径が均熱時間の増加によって５μm から18μm へと増加しているためであることがわかった。
【００６３】
最終冷間圧延直前の結晶粒径は、このように一次再結晶集合組織に大きな影響をもたらすことは、これまでにも知られていたが、従来の製造方法では、中間焼鈍あるいは熱延板焼鈍温度が高温であるため、結晶粒径を変更するために均熱温度を変えた場合、インヒビターの抑制力も変化することから、中間焼鈍、熱延板焼鈍の際にインヒビターの抑制力を維持しつつ、この最終冷間圧延直前の結晶粒径を適正範囲に独立して制御することができなかった。
【００６４】
これに対して、この発明に従う1125℃以下の低温の焼鈍においては、インヒビターの析出状態を変えることなく、結晶粒径を変更できるようになり、これによってはじめて、適正な一次再結晶集合組織に制御することが可能となったものである。なお、最終冷間圧延前の適正な平均結晶粒径は、10〜35μm であり、より好ましくは12.5〜27.5μm であり、これらの平均結晶粒径は、鋼の成分や、焼鈍温度、焼鈍時間、焼鈍雰囲気の変更によって調節することが可能である。
【００６５】
なお、集合組織制御の方法に関しては、従来から公知の方法があり、例えば150 〜250 ℃での温間圧延や、パス間時効及び最終冷間圧延前の焼鈍の冷却途中における低温度での温度保持によるカーバイドの析出ないし析出物サイズの制御の技術が挙げられ、この発明の方法と組み合わせることにより、一層効果が高まる。
【００６６】
最終的ににAl含有方向性電磁鋼板において、｛１１１｝〈１１２〉粒の形成頻度及び（１１０）〔００１〕粒の形成頻度を高めるには、公知のように最終冷間圧延の圧下率を80〜95％とすることが必要で、この範囲を外れた場合には、｛１１１｝〈１１２〉粒の形成頻度の急激な低下を招き、磁気特性の劣化がもたらされる。
【００６７】
更に、この発明の方向性電磁鋼板の磁気特性を向上させるには、公知のように鋼中のSbを添加し、このSbの粒界及び表面への偏析効果を利用して、二次再結晶の制御を行うことが有効であり、このためには、二次再結晶焼鈍の昇温時に800 〜890 ℃の間で15〜60時間、一定温度に保持するか、５℃/hr 以下の昇温速度又は降温速度で昇温又は降温処理を施す。これにより、二次再結晶の結晶方位をより先鋭なものとすることができる。
【００６８】
以下、この発明の出発素材となる方向性電磁鋼スラブの成分について述べる。
〔Ｃ：0.10％以下〕
Ｃは、γ変態を利用して熱延組織を改善するために必要であるが、場合によっては脱炭工程を行わずして製造することもあり、これらを勘案して適量を含有させる。一方0.10％を超えると脱炭不良となるので、0.10％以下とする。
【００６９】
〔Si：2.5 〜5.0 ％〕
Siは、電気抵抗を高めて鉄損を向上させるため2.5 ％以上が必要である。一方、5.0 ％を超えるとぜい化が激しく、冷間圧延が困難となるので、2.5 〜5.0 ％の範囲とする。
〔 Mn ： 0.005 〜 0.10 ％〕
Mn は、熱間圧延時の割れを防止するのに有用であり、また、 MnS や MnSe 等の副インヒビターを利用する際には、インヒビター形成成分としても有用となる。このためには 0.005 ％以上の含有が必要であり、上限としては副インヒビター形成のために 0.10 ％までを含有量とする。すなわち、 0.10 ％を超えると析出物として粗大化し、インヒビターとしての抑制力が低下し、磁気特性が劣化する。
【００７０】
〔Al：0.005 〜0.04％〕
Alは、この発明で所期した高磁束密度の方向性電磁鋼板を得るために必須の主インヒビターであるところのAlN を析出させるための基本成分であり、0.005 ％未満ではAlN の析出量が足りず、逆に0.04％を超えると析出するAlN が粗大化して抑制力が劣化するので、0.005 〜0.04％の範囲とする。
【００７１】
〔Ｎ：0.0040〜0.0130％〕
Ｎもこの発明で所期した高磁束密度の方向性電磁鋼板を得るために必須の主インヒビターであるところのAlN を析出させるための基本成分である。このＮは、鋼スラブ中に所定量を含有させることは必ずしも必要でなく、製造工程の途中で窒化処理により補給することも可能であるが、鋼スラブ中のＮ量が0.0040％未満ではこの発明の場合、AlN の量として不十分となる。逆に0.0130％を超えると鋼スラブの加熱の際にガス化して、フクレ等のトラブルの原因になるので、0.0040〜0.0130％の範囲とする。
【００７２】
以上、述べたＣ、Si、Mn 、Al及びＮは、この発明に必須の成分であり、その他の成分は不純物を除けば本質的にFeであっても十分である。
しかしながら、この発明の効果を高めるためには、次に述べる公知の成分を更に含有させることは可能である。
【００７４】
Cuは、硫化物、セレン化物などを形成するので有用成分であるが、この目的のためには0.005 ％以上が必要である。ただし、0.30％を超えると析出物として粗大化し、インヒビターとしての抑制力が低下してその効力を失う。
【００７５】
Ｓ、Seは、Mn又はCuと結合して副インヒビターとしてのMnS ，MnSeやCuS ，CuSeを析出させるので有用な成分である。この効果をもたらすためには、合計で0.005 ％以上が必要であるが、一方、0.030 ％を超えると、析出物の粗大化が生じ、磁気特性の劣化を招くので、0.005 〜0.030 ％の範囲が好ましい。
【００７６】
Sbは、鋼板表層部の酸化及び窒化を抑え、二次再結晶焼鈍における核の選択性を高めるので有効な成分であり、また、結晶粒界に偏析して抑制力を補強する効果を有する。これらの効果のためには、0.005 ％以上の含有が必要であるが、0.060 ％を超えると鋼板のぜい化が甚だしくなるので、0.005 〜0.060 ％の範囲が好ましい。
【００７７】
さらに、他にインヒビター補強成分として公知であるSn、Ｐ、Bi、As、Ｂ、Ge、Ｖ、Nb、Cr、Te等を含有してもよいことは勿論である。この目的のためには、Sn、Crは0.03〜0.30％、Biは0.005 〜0.020 ％、Ｐ、Ge、Ｖ、Nb、As、Teは0.005 〜0.030 ％、Ｂは0.0005〜0.0020％の範囲の含有が好ましい。
加えて、方向性電磁鋼に特有の熱間圧延での割れを防止するために、Moを0.005 〜0.020 ％含有させることも可能である。
【００７８】
次に、この発明における製造工程の要件について説明する。
上記成分を含有する方向性電磁鋼は、熱間圧延により熱延鋼帯とされる。このとき、ＳやSeなどの副インヒビター成分を含有する場合は、高温スラブ加熱を施すが、インヒビターとしてAlN のみを利用する場合は、通常の1200℃前後のスラブ加熱や連続鋳造後の高温スラブを直接圧延することも可能である。
【００７９】
ここで、粗圧延と仕上圧延からなる熱間圧延において、粗圧延開始から仕上圧延終了までの時間として450 秒間未満からなる通常の方向性電磁鋼の熱間圧延の場合には、熱間圧延の仕上圧延の開始温度を1000〜1230℃とし、終了温度を800 〜1100℃とする。この温度範囲に調整することによって、AlN を高密度に析出分散させることができ、ひいては磁気特性の優れた製品が得られるからである。この理由は、まだ完全に解明されたわけではないが、かかる温度域での仕上圧延によって、極微細な積層欠陥、硫化物、セレン化物、酸化物が高密度に形成され、次工程での熱延板焼鈍の昇温過程で析出する微細AlN の析出サイトが十分に形成されることになるものと推定される。
【００８０】
ここで、かかる仕上圧延温度がこの範囲よりも高い場合、微細AlN の析出サイトの形成量が十分でなく、該析出AlN が粗大化し、析出頻度も低下する結果、抑制力の低下をもたらし、製品の磁気特性が劣化する。また、かかる仕上圧延温度がこの範囲よりも低い場合も、析出サイトの形成量が不十分となり、熱延板焼鈍の昇温過程で析出するAlN が粗大化して、抑制力の低下をもたらし、製品の磁気特性が劣化する。
【００８１】
また、鋼中にＳ及び／又はSe並びに Cuを含有する場合は、より明確に極微細CuS 、CuSe、MnS 又はMnSeの析出物が形成され、熱延板焼鈍の昇温過程で析出する微細AlN の析出サイトとして特に有効に寄与する。このとき、この効果を顕著に発現させるためには、熱間圧延の仕上圧延の開始温度を1000〜1200℃、終了温度を850 〜1000℃とすることが好ましい。温度の限定理由は、上述と同様である。
【００８２】
一方、圧延機配列が長大となったり、仕上圧延機がリバース方式である等の理由により、粗圧延開始から仕上圧延終了までの時間が450 秒間以上となる熱間圧延の場合にも、この発明は極めて効果的である。なお、このときは鋼中にSeを含有させることが必要である。その理由は、Seを含有させることによりCu_x SeやMnSeが析出するのであるが、このCu_x SeやMnSeは析出温度が低く、Seの拡散速度が遅いため、低温で長時間の熱間圧延においても、極微細な析出物を十分に得ることが可能となるからである。
【００８３】
かかる場合の熱間圧延の適正条件としては、熱間圧延の仕上圧延開始から終了までの時間を460 秒間以下として、仕上圧延終了温度を850 〜1150℃とすることが必要であり、かかる条件によって、次工程の熱延板焼鈍の昇温過程で析出する微細AlN の析出サイトが十分に形成されることになるものと推定される。
【００８４】
仕上圧延の開始から終了までの時間が460 秒間を超える場合もしくは熱間圧延終了温度が850 〜1150℃の温度範囲から外れる場合は、この発明の方法をもってしても粗大なCu_x SeやMnSeに複合析出した粗大結晶質AlN の析出を抑制し得ず、AlN の粗大化をもたらし、よってインヒビターの抑制力の改善効果がなく、製品の磁気特性が劣化する。
【００８５】
次に、かかる熱間圧延の終了後は、鋼板の急速冷却により700 ℃までの冷却速度を10℃/s以上とし、コイル巻き取り温度として650 ℃以下とすることが必要である。この条件は、熱間圧延の際に、粗圧延開始から仕上圧延終了までの時間が450 秒未満である場合であっても、450 秒以上である場合であっても同じである。
【００８６】
かかる急冷、低温巻取り処理によって、有害な結晶質（Si，Al）Ｎが鋼中に生成することを防止し、次工程である熱延板焼鈍の昇温過程で、微細なAlN を新たに析出させることができ、これによりインヒビターAlN の抑制力を向上させることができるのである。
【００８７】
逆に、700 ℃までの冷却速度が10℃/s未満の場合や、コイル巻き取り温度が650 ℃を超える場合は、熱的に安定な結晶質（Si，Al）Ｎの析出温度領域に長時間滞留することになるから、熱延板焼鈍の昇温過程で新たに析出する微細AlN の量が不足して、インヒビターAlN の抑制力を向上させることが叶わず、磁気特性が劣化する。なお、ここで析出する結晶質（Si，Al）Ｎは次工程以降でSiとAlとの置換が進行し、究極にはAlN に転換するとはいえ、そのサイズはおおよそ変化することがないので、初期に析出した粗大なサイズが最後まで保存されてしまい、インヒビター抑制力の向上には寄与しない。
【００８８】
熱間圧延後の鋼板は、熱延板焼鈍が施され、１回又は中間焼鈍を挟む２回の冷間圧延によって最終板厚とされる。
ここに、熱延板焼鈍の昇温過程は、この発明において最も重要な工程の一つであって、600 〜800 ℃の昇温速度を５〜30℃/sとすることが肝要である。かかる昇温速度の制御によって、熱間圧延段階で多量に生起させたAlN の析出サイト上に微細AlN を高密度に生成させる。この微細AlN は600 ℃前後から析出を開始し、800 ℃程度で大部分が析出するので、この温度領域での昇温速度が重要となるである。
【００８９】
ここに、かかる温度領域での昇温速度が30℃/sを超える場合は、析出サイトにAlN が高密度かつ微細に析出するが、鋼中の場所によっては析出密度の不十分な領域も存在し、均一微細かつ高密度の析出とはならない。逆に昇温速度が５℃/s未満の場合は、析出頻度が低下し、析出物のサイズが増大する。このように、600 〜800 ℃の昇温速度がこの発明の範囲を外れる場合はいずれもインヒビター抑制力の低下をもたらすので、製品の磁気特性の劣化をもたらす。
【００９０】
以上のことから、この発明の主インヒビターである微細AlN の析出のサイズ、析出頻度、均一性等の分散制御は、かかる熱延板焼鈍の昇温過程の600 〜800 ℃での昇温速度の制御によってなされるといえる。
【００９１】
かかる昇温速度の制御によって分散析出させた微細AlN は、冷間圧延直前の焼鈍時に、オストワルド成長や固溶・再析出により、分散状態が劣化する可能性が高いので、この発明では、この焼鈍の上限温度を従来より低く、1125℃以下とすることが特に肝要である。すなわち、通常行われている1150℃や1200℃等といった高温の焼鈍では、AlN のオストワルド成長（α−Feの部分）及び固溶・再結晶（γ−Feの部分）をさせることにより、AlN の好適な分散析出状態を得ることを目的としているが、この方法では先に述べた実験結果からも示されるように、この発明の方法と比較して、AlN の微細・均一分散の手法として劣っており、この発明におけるような強い抑制力効果を得ることはできないのである。したがって、この発明における熱延板焼鈍及び最終冷間圧延前の焼鈍の最高温度は、1125℃とする。
【００９２】
更に、かかる焼鈍温度の下限値については特に定めないが、AlN の昇温時における析出制御の観点及び実施例でも示されるように、最終冷間圧延直前の平均結晶粒径制御の観点からも1000℃を超えることが望ましい。
【００９３】
更に、この発明の第３の技術として、最終冷間圧延直前の鋼板の平均結晶粒径を制御することで、一次再結晶集合組織を制御することがある。すなわち、最終冷間圧延前の鋼板の平均結晶粒径を10〜35μm に制御することが必要であり、より好ましくは12.5〜27.5μm に制御することが望ましい。
このように最終冷間圧延直前の鋼板粒径を10〜35μm の範囲に調整することにより、（１１０）〔００１〕粒の生成頻度を増加させ、かつ｛１１１｝〈１１２〉粒の生成頻度を調整することができ、ひいては（１１０）〔００１〕方位からずれた方位の一次再結晶粒の二次再結晶粒としての成長を抑制して製品の二次再結晶粒の（１１０）〔００１〕方位への集積を高めることができ、磁気特性のさらなる向上をもたらすことができる。
【００９４】
ここで、鋼板の平均結晶粒径が10μm 未満の場合には、一次再結晶集合組織において、｛１１１｝〈１１２〉粒の生成頻度が過剰となり、二次再結晶の核として（１１０）〔００１〕方位からずれた方位の結晶粒が多く成長する結果、製品の二次再結晶方位の劣化をもたらし、磁気特性が劣化する。
また、逆に鋼板の平均粒径が35μm を超える場合には、一次再結晶集合組織においても｛１１１｝〈１１２〉粒の生成頻度が低減し、二次再結晶の核としての（１１０）〔００１〕粒の成長さえも抑制される結果、二次再結晶不良が発生し、製品の磁気特性の劣化をもたらす。
【００９５】
なお、ここで平均結晶粒径の測定方法は、鋼板の板厚方向の断面であって一方の表層から他方の表層までにわたる領域において、1000個以上の結晶粒の個数を測定し、一個当たりの面積より、円相当径に換算して算出したものである。
【００９６】
上記のような最終冷間圧延直前の鋼板における平均結晶粒径の調整は、主として熱延板焼鈍や中間焼鈍での焼鈍温度や時間の変更で行うことができ、これによって平均結晶粒径制御とインヒビターの分散制御を全く独立にできる点がこの発明の優れている点である。すなわち、熱延板焼鈍の昇温速度によりインヒビターの分散制御を行った後は、1125℃以下の温度で焼鈍温度と時間とを変えることにより、平均結晶粒径の適切な制御を行うことが可能である。この平均結晶粒径の制御は、上記の手段の他にも、焼鈍雰囲気や鋼中成分の変更によっても行うことが可能で、これらを併用することも有効である。
【００９７】
また、鋼中にＣを含有する鋼の場合には、最終冷間圧延直前の焼鈍の冷却過程において、急冷低温保持によって微細カーバイドの析出促進や、析出サイズの調整を行って、一次再結晶集合組織の制御を行うことも有用な手段であり、この発明をこの適用を妨げない。更に、冷間圧延において、150 〜250 ℃の温度での温間圧延や、パス間時効処理によって一次再結晶集合組織の制御を行うことも有効な手段であり、この発明はこの適用を妨げない。
【００９８】
次に、この発明で所期するような高磁束密度の方向性電磁鋼板を得るためには最終冷間圧延の圧下率を80〜95％の高圧下とすることが必要であり、この範囲の圧下率を施すことにより、一次再結晶集合組織として、二次再結晶核が成長し易い｛１１１｝〈１１２〉粒の形成頻度を高めることができる。すわなち、圧下率が80％未満や95％を超える場合は、一次再結晶組織における｛１１１｝〈１１２〉粒の生成頻度が急激に低下し、二次再結晶の核の成長が困難となる。
【００９９】
上記の最終冷間圧延後のコイルは、次いで一次再結晶焼鈍に供される。この焼鈍は、鋼中にＣを含有する場合には脱炭焼鈍を兼ねている。この焼鈍は、750 〜900 ℃、60〜180 秒間で行われる。
【０１００】
一次再結晶焼鈍後のコイルは、焼鈍分離剤を塗布した後、コイル状に巻き取ってから二次再結晶焼鈍に供する。この二次再結晶焼鈍は、純化焼鈍を兼ねて最終仕上焼鈍として施すことが一般的である。この最終仕上焼鈍は、公知の方法で行えば良いが、特にこの発明ではSbを鋼中に含有させ、昇温途中で800 〜890 ℃の間で15〜60時間の一定温度保持の処理か、もしくは５℃/hr 以下の昇温速度又は降温速度の昇温処理又は降温処理を施すことが、二次再結晶粒の結晶方位を（１１０）〔００１〕方位に集積させるのに有効である。
【０１０１】
最終仕上焼鈍後のコイルは、残存する焼鈍分離剤を除去したのち、絶縁抵抗を高める必要のある場合には絶縁コーティング剤を塗布して平坦化焼鈍を施し、製品とされる。また、製品は、プラズマジェット、レーザーもしくは電子ビームの照射や溝形成等の磁区細分化技術を適用することは可能で、この発明の目的とも合致する。
【０１０２】
【実施例】
（実施例１）
表３に示す成分組成になる鋼塊記号Ｃ〜Ｍのスラブを各２本ずつ準備した。これらのスラブを誘導加熱炉で1400℃に加熱した後、３機直列配置になる粗圧延機及び７スタンドのタンデム圧延機からなる仕上圧延機を用いた熱間圧延により板厚2.20mmの熱延コイルとした。
【０１０３】
【表３】

【０１０４】
この熱間圧延においては、粗圧延でのクーラント水量の調整により各鋼種２本のスラブにつき、一方は仕上圧延開始温度を1150〜1220℃とし、仕上圧延終了温度を890 〜970 ℃とし、その後はジェット水を鋼帯に噴射することにより18℃/sの冷却速度で急冷してから、550 ℃でコイル状に巻き取った（適合例）。
【０１０５】
他方は、仕上圧延開始温度を1250〜1310℃とし、仕上圧延終了温度を1120〜1190℃とし、その後はジェット水を鋼帯に噴射することにより８℃/sで冷却してから、巻き取りは適合例と同じく550 ℃で行った（比較例）。なお、粗圧延開始から仕上圧延終了までの所要時間は、いずれも230 〜290 秒間の範囲であった。
【０１０６】
熱間圧延終了後は、各鋼板を1000℃で30秒間の熱延板焼鈍を施した、このとき、昇温温度を15〜17℃/s（600 〜800 ℃間の昇温速度13〜16℃/s）とした。この後、酸洗により表面のスケールを除去してから、冷間圧延により中間板厚1.40mmとし、次いで中間焼鈍を施した。この中間焼鈍の条件は、適合例の鋼板については露点50℃、50％Ｈ₂ 、残部Ｎ₂ バランスの雰囲気中で1080℃で60秒間の熱処理を施したのち、ミスト水を用いて40℃/sの冷却速度で350 ℃まで急冷し、この350 ℃にて20秒間保持した後、冷却し酸洗したものである。一方、比較例の鋼板の中間焼鈍条件については、適合例と同一の雰囲気中で1170℃で60秒間の熱処理を施したのち、ミスト水を用いて40℃/sの冷却速度で室温まで急冷した後、酸洗したものである。
【０１０７】
これらの鋼板について、中間焼鈍後の鋼板の平均結晶粒径を測定したのち、150 〜220 ℃で温間圧延及びパス間時効を施し、0.19mmの最終板厚に仕上げた。
これらの鋼板は、露点60℃、55％Ｈ₂ と残部Ｎ₂ バランスの雰囲気中で840 ℃，120 秒間の脱炭・一次再結晶焼鈍を施し、次いで５％のTiO₂と３％のSrSO₄ とを含有するMgO を焼鈍分離剤として塗布した後、コイル状に巻き取って最終仕上焼鈍を施した。
【０１０８】
この最終仕上焼鈍の条件は、以下のとおりである。まず、Sbを含有する記号Ｃ，Ｅ，Ｈ，Ｋ，Ｍのコイルについては、850 ℃までを30℃/hr の昇温速度でＮ₂ 中で昇温し、さらにＮ₂ 中で850 ℃で35時間保持した後、25％Ｎ₂ と75％Ｈ₂ の混合雰囲気中で15℃/hr の昇温速度で1160℃まで昇温し、Ｈ₂ 中で1160℃、８時間保持した後、降温した。
また、記号Ｄ，Ｆ，Ｇ，Ｉ，Ｊ，Ｌのコイルについては、850 ℃まで30℃/hr の昇温速度でＮ₂ 中で昇温し、さらに25％Ｎ₂ と75％Ｈ₂ の混合雰囲気中で15℃/hr の昇温速度で1160℃まで昇温し、Ｈ₂ 中で1160℃、８時間保持した後、降温した。
【０１０９】
最終仕上焼鈍後は、残像する焼鈍分離剤を除去した後、50％のコロイダルシリカとりん酸マグネシウムからなる張力コーティング剤を塗布した後、800 ℃，１分間のコーティング焼き付けを兼ねる平坦化処理を施し、更に圧延方向に６mmの間隔で線状にプラズマジェットを照射して磁区細分化処理を施して製品とした。これらの製品の磁気特性をを表４に示す。
【０１１０】
【表４】

【０１１１】
表４から明らかなように、この発明に従う熱間圧延及び冷間圧延条件を満たす適合例は、比較例に比し極めて優れた磁気特性を有している。
【０１１２】
（実施例２）
表３に示した鋼塊記号Ｃ，Ｄ，Ｈ，Ｉのスラブを各２本ずつ準備した。これらのスラブを1350℃に加熱したのち、粗圧延機による粗圧延とステッケル圧延機による仕上圧延とからなる熱間圧延によって2.40mmの板厚の熱延コイルとした。
【０１１３】
この熱間圧延では、仕上圧延開始温度を980 〜1125℃とし、仕上圧延終了温度を870 〜1020℃とし、粗圧延開始から仕上圧延終了まで490 〜510 秒間を要した。熱間圧延終了後は各鋼種につき、一方のコイルはジェット水を噴射して20℃/sの冷却速度で500 ℃まで急冷した後、コイル状に巻き取り放冷した（適合例）。一方、残るコイルは熱延終了後、５℃/sの冷却速度で500 ℃まで急冷したのち、コイル状に巻き取り放冷した（比較例）。
【０１１４】
これらの熱延コイルには、次いで1100℃で60秒間の熱延板焼鈍を施したが、このとき、昇温時の加熱制御を行い、600 〜800 ℃間の昇温速度を8.5 〜10.5℃/sの間に制御し、かつ、冷却時にはミスト冷却により冷却速度20℃/sとして鋼中に微細カーバイドを析出させた。この熱延板焼鈍後は鋼板の平均結晶粒径を測定し、酸洗後、150 〜250 ℃での温間圧延とパス間時効により最終板厚0.34mmまで圧延した。
【０１１５】
最終冷間圧延後は電解脱脂し、次いで露点60℃、Ｈ₂ 55％、残余Ｎ₂ バランスの雰囲気で脱炭・一次再結晶焼鈍を施した後、８％TiO₂を含有するマグネシアを焼鈍分離剤として塗布した後、コイル状に巻き取り最終仕上焼鈍に供した。
この最終仕上焼鈍の条件は、Ｎ₂ 中で800 ℃まで30℃/hr の昇温速度で昇温し、その後20％Ｎ₂ と80％Ｈ₂ の雰囲気で1180℃まで15℃/hr の昇温速度で昇温してから、Ｈ₂ 雰囲気中で1180℃、５時間保持した後、降温したものである。
最終仕上焼鈍後は残存する焼鈍分離剤を除去した後、50％のコロイダルシリカとりん酸アルミニウムからなる張力コーティング剤を塗布した後、800 ℃、１分間のコーティング焼き付けを兼ねる平坦化処理を施し、製品とした。
これらの製品の磁気特性を表５に示す。
【０１１６】
【表５】

【０１１７】
表５から明らかなように、Seをインヒビター成分として添加した鋼Ｃ，Ｈについて、この発明に従う熱間圧延及び冷間圧延条件を満たす場合に、極めて優れた磁気特性が得られる。
【０１１８】
（実施例３）
表３に示す鋼塊記号Ｃのスラブを16本用意し、これらのスラブを誘導加熱炉で1420℃に加熱し、実施例１と同一の熱間圧延機配列で粗圧延及び仕上圧延を施し、2.40mmの板厚の熱延コイルとした。このとき、粗圧延でのロールクーラント及びストリップクーラント水量の調節により、仕上圧延開始温度を1170〜1210℃とし、仕上圧延終了温度を870 〜930 ℃とし、その後、ジェット水を噴射して15℃/sの冷却速度で急冷してから550 ℃でコイル状に巻き取った。このとき、粗圧延開始から仕上圧延終了までの所要時間は350 〜372 秒間であった。
【０１１９】
熱間圧延後は、各鋼板とも950 ℃で60秒間の熱延板焼鈍を施したが、このとき、昇温速度を調整し、600 〜800 ℃間の昇温速度を12〜15℃/sとした。この後、酸洗により表面スケールを除去し、次いで冷間圧延により1.50mmの板厚に圧延した後、中間焼鈍を施した。この中間焼鈍の条件として、雰囲気を２水準にとり、一つは乾燥雰囲気条件（露点10℃以下、20％Ｎ₂ と80％Ｈ₂ ）であり、もう一つは湿潤雰囲気条件（露点50℃、50％Ｎ₂ と残余Ｈ₂ バランス）とした。また、均熱温度を1080と一定にして均熱時間をそれぞれ５秒間、10秒間、30秒間、60秒間、90秒間、120 秒間、180 秒間、240 秒間とした。この焼鈍後はミスト水で40℃/sの冷却速度で350 ℃まで急冷し、この350 ℃で25秒間保持した後、冷却し酸洗した。次いで、これらの鋼板の平均結晶粒径を測定した後、100 〜230 ℃で温間圧延を施し最終板厚0.22mmに仕上げた。
【０１２０】
次に脱脂処理を施し、磁区細分化処理の溝を設けるため、鋼板に耐酸性のマスキング処理を選択的に施して、非処理部を電解エッチングし、幅150 μm 、深さ20μm の、圧延方向から85°の方向に伸びる溝を圧延方向における間隔４mmで設けた。
【０１２１】
次にこれらの鋼板に露点50℃、55％のＨ₂ と残部Ｎ₂ バランスの雰囲気中で850 ℃、120 秒間の脱炭・一次再結晶焼鈍を施してから、８％のTiO₂と３％の Sr(OH)₂・８H₂O を含有するMgO を焼鈍分離剤として塗布した後、コイル状に巻き取り最終仕上焼鈍を施した。
この最終仕上焼鈍の条件は、Ｎ₂ 中で840 ℃，45時間保持した後、15％Ｎ₂ と85％Ｈ₂ との混合雰囲気で20℃/hr の昇温速度で1160℃まで昇温し、Ｈ₂ 中で1160℃、５時間保持してから降温したものである。
【０１２２】
この最終仕上焼鈍後は、残存する焼鈍分離剤を除去したのち、50％のコロイダルシリカとりん酸マグネシウムからなる張力コーティングを塗布した後、800 ℃、１分間のコーティング焼き付けを兼ねる平坦化処理を施し、製品とした。
これらの製品の磁気特性と中間焼鈍後の鋼板の平均結晶粒径との関係を図３に示す。この図３に示されるように、この発明に従い、鋼板の平均結晶粒径が10〜35μm である範囲において、優れた磁気特性の製品が得られている。
【０１２３】
（実施例４）
表３に示す鋼塊記号Ａ，Ｂのスラブを各３本ずつガス炉で1200℃に加熱し、実施例１と同一の熱間圧延機配列により粗圧延及び仕上圧延を施し、Ａ、Ｂ共に２本は、板厚2.70mmに、残り１本は板厚2.00mmに熱間圧延して熱延コイルとした。この熱間圧延の際、仕上圧延開始温度を1030〜1090℃とし、仕上圧延終了温度を830 〜890 ℃とした。この仕上圧延終了後はジェット水を噴射して14℃/sの冷却速度で急冷し、550 ℃でコイル状に巻き取った。このときの粗圧延開始から仕上圧延終了までの所要時間は284 〜320 秒であった。
【０１２４】
熱間圧延後は、均熱温度1000℃の熱延板焼鈍を施したが、このとき、板厚2.70mmの熱延板の一方は600 〜800 ℃間の昇温速度を３℃/sとし、他方は急熱処理により600 〜800 ℃間の昇温速度を14℃/sとした。また、板厚2.00mmの熱延板は600 〜800 ℃間の昇温速度を16℃/sとした。なお、均熱時間は、平均結晶粒径を18〜21μm とするため、50秒間とした。これらの鋼板は、平均結晶粒径を測定した後、250 ℃での温間圧延により0.49mmの最終板厚に仕上げた。
【０１２５】
この後、脱脂処理を施し、鋼Ａについては露点60℃、50％Ｈ₂ 残部Ｎ₂ バランスの雰囲気下で840 ℃、200 秒間の脱炭・一次再結晶焼鈍を施し、また、鋼Ｂについては露点40℃、40％Ｈ₂ 、残部Ｎ₂ バランスの雰囲気下で840 ℃、60秒間の一次再結晶焼鈍を施した。この後は５％のTiO₂を含有するMgO 焼鈍分離剤を塗布してコイル状に巻き取り、最終仕上焼鈍を施した。
【０１２６】
この最終仕上焼鈍の条件は、Ｎ₂ 中900 ℃まで30℃/hr の昇温速度で昇温し、次いで25％Ｎ₂ と75％Ｈ₂ との混合雰囲気で1180℃まで15℃/hr の昇温速度で昇温して、引き続きＨ₂ 中で1180℃で５時間保持したのち、降温したものである。
【０１２７】
最終仕上晶緒後は残存する焼鈍分離剤を除去した後、50％のコロイダルシリカとりん酸マグネシウムからなる張力コーティングを塗布した後、800 ℃，１分間のコーティング焼き付けを兼ねる平坦化処理を施して製品とした。これらの経遺品の磁気特性を表６に示す。
【０１２８】
【表６】

【０１２９】
表６に示されるように、この発明に従う熱間圧延工程及び冷間圧延工程の条件を満たす製品は、優れた磁気特性を示している。
【０１３０】
（実施例５）
表３に示した鋼塊記号Ｋのスラブを８本準備した。これらのスラブを1400℃に加熱し、１機の粗圧延機と６スタンドの仕上圧延機からなる熱間圧延設備によって、往復による３回の粗圧延と仕上圧延を施し、2.20mmの熱延コイルとした。このとき、粗圧延でのクーラント水量を調節して仕上圧延開始温度を1100〜1150℃、仕上圧延終了温度を920 〜970 ℃とし、仕上圧延終了後はジェット水を噴射して16℃/sの冷却速度で急冷し500 ℃でコイル状に巻き取った。このときの粗圧延開始から仕上圧延終了までの所要時間は198 〜216 秒間であった。
【０１３１】
熱間圧延後、昇温速度10℃/s（600 〜800 ℃間にて12℃/s）で均熱温度1000℃の熱延板焼鈍を施し、酸洗後、冷間圧延により1.50mmの中間板厚とした。引き続く中間焼鈍は、露点45℃、60％Ｈ₂ 、残部Ｎ₂ バランスの雰囲気で均熱時間60秒間の熱処理であって、引き続きミスト水により40℃/sの冷却速度で急冷処理をするものであるが、この中間焼鈍の均熱時間をそれぞれ1000℃、1050℃、1075℃、1100℃、1125℃、1150℃、1175℃、1200℃に変更した。
【０１３２】
この中間焼鈍後の鋼板は、平均結晶粒径を測定した後、酸洗を施し、次いで、150 〜230 ℃の温間圧延とパス間時効からなる冷間圧延によって最終板厚0.22mmまで仕上げた。
【０１３３】
この後、脱脂処理を施し、露点60℃，50％Ｈ₂ 、残部Ｎ₂ バランスの雰囲気下で840 ℃，120 秒間の脱炭・一次再結晶焼鈍を施し、次いで８％のTiO₂を含有するMgO 焼鈍分離剤を塗布してからコイル状に巻き取って最終仕上焼鈍に供した。この最終仕上焼鈍条件は、860 ℃までＮ₂ 中で40℃/hr の昇温速度で昇温し、引き続いてこの860 ℃で25時間Ｎ₂ 中で保持した後、25％Ｎ₂ と75％Ｈ₂ の雰囲気で12℃/hの昇温速度で1200まで昇温してから、Ｈ₂ 中で1200℃で５時間保持した後、降温したものである。
【０１３４】
最終仕上照度後は、残存する焼鈍分離剤を除去したのち、磁区細分化処理として突起ロールで幅100 μm 、深さ15μm 、圧延方向から85°に伸びる溝を圧延方向に４mmの間隔で形成し、次いで50％のコロイダルシリカとりん酸マグネシウムからなる張力コーティングを塗布した後、800 ℃、１分間のコーティング焼き付けを兼ねる平坦化処理を施し、製品とした。
これらの製品の磁気特性を表７に示す。
【０１３５】
【表７】

【０１３６】
表７に示されるように、中間焼鈍後の平均結晶粒径が8.2 μm と小さい、均熱温度：1000℃の条件の製品及び均熱温度1150℃，1175℃、1200℃とこの発明の均熱温度よりも高い条件の製品については、磁気特性が劣っているが、この発明に従う冷間圧延工程を満たす製品については、極めて良好な磁気特性が得られている。
【０１３７】
【発明の効果】
かくしてこの発明によれば、Alを含有する方向性電磁鋼板を製造する際、熱間圧延工程の各種条件の制御及び冷間圧延条件の制御によるインヒビターAlN の新しい析出制御の方法によって、極めて優れた磁気特性の方向性電磁鋼板を得ることができる。
【図面の簡単な説明】
【図１】この発明に従う熱延板、熱延板焼鈍の1000℃昇温直後の鋼板及び脱炭・一次再結晶焼鈍後の析出物の粒径分布と生成頻度とを示す図である。
【図２】従来の熱延板、熱延板焼鈍の1000℃昇温直後の鋼板及び脱炭・一次再結晶焼鈍後の析出物の粒径分布と生成頻度とを示す図である。
【図３】実施例における中間焼鈍後の鋼板の平均結晶粒径と磁気特性との関係を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing a grain-oriented electrical steel sheet having a crystal orientation aligned in one direction, which is used for a core material such as a transformer.
[0002]
[Prior art]
In recent years, from the standpoint of energy crisis and environmental protection, it is desired to improve the efficiency of electrical equipment. Iron loss of iron cores of transformers and rotating machines (loss W when magnetized to a magnetic flux density of 1.7 T at 50 Hz)_17/50Represented by ) Is required.
[0003]
In recent years, with regard to grain-oriented electrical steel sheets as iron core materials, technologies have been developed that significantly reduce iron loss by magnetic domain refinement techniques such as laser irradiation or plasma irradiation on the steel sheet surface or grooves in the steel sheet surface. , Magnetic flux density (value B at a magnetic field strength of 800 A / m₈Indicated by ) Is becoming increasingly important for reducing iron loss.
[0004]
In order to improve the magnetic flux density of the grain-oriented electrical steel sheet, it is necessary to highly integrate the crystal grain orientation of the product in the (110) [001] orientation, so-called Goth orientation. Here, the crystal grains in the Goss direction are obtained by the secondary recrystallization phenomenon caused by the final finish annealing, and in order to cause this secondary recrystallization, it is close to the (110) [001] orientation. In order to suppress so-called selective growth by growing only crystal grains and suppressing generation of crystal grains in other directions, an inhibitor (inhibitor) for suppressing the growth of crystal grains in other directions is necessary. That is, the inhibitor forms a precipitated dispersed phase in the steel and exhibits a function of suppressing grain growth.
[0005]
As such an inhibitor, the one having the strongest inhibitory action has the strongest selective growth effect, and a material having a high magnetic flux density can be obtained. Therefore, many studies have been made so far to find an inhibitor having a strong inhibitory action. The most effective one was AlN. That is, as disclosed in Japanese Examined Patent Publication No. 46-23820, a steel sheet containing Al is rapidly cooled by annealing before the final cold rolling, and the rolling reduction of the final cold rolling is 80 to 95%. With the thickness of 0.35mm, B_TenIs 1.981 T (B₈A material with a high magnetic flux density of about 1.95 T) is obtained. However, with this method, the greatest problem is that excellent magnetic properties cannot be stably obtained.
[0006]
Japanese Examined Patent Publication No. Sho 63-11406 discloses a technique for stably producing a grain oriented electrical steel sheet of 0.15 to 0.25 mm by adding Sn and Cu to steel and using a cold rolling method. The magnetic flux density of products obtained by this technology is B_Ten1.92T (B₈About 1.90 T), which is not yet sufficient as a magnetic flux density magnetic steel sheet.
[0007]
Further, as a method for enhancing the inhibitory inhibitory power of grain-oriented electrical steel sheets containing Al, a method of nitriding a steel sheet surface layer portion has been known for a long time. For example, JP-A-49-6455 discloses decarburization. A technique for performing nitriding after the annealing process is disclosed in Japanese Patent Publication No. 50-19489, and a technique for performing nitriding in the process before the final cold rolling is disclosed. However, the magnetic flux density of products obtained by these technologies is at most B_Ten: 1.93T (B₈About 1.91 T), and a material having a high magnetic flux density has not been obtained.
[0008]
By the way, in order to obtain a good secondary recrystallization, it is necessary to control not only the strong inhibitory force of the inhibitor described above but also a suitable texture of primary recrystallized grains. That is, in the texture of such primary recrystallized grains, the generation frequency of secondary recrystallized nuclei aligned in the (110) [001] orientation (hereinafter referred to as (110) [001] grains) increases ( 110) It is important to increase the frequency of formation of {111} <112> -oriented grains (hereinafter referred to as {111} <112> grains) in which grains with [001] orientation tend to grow.
[0009]
Among the grain control of the primary recrystallization texture, it is known that increasing the frequency of forming the latter {111} <112> grains can be achieved by increasing the rolling reduction of the final cold rolling. Therefore, generally a rolling reduction of 80% or more is adopted. On the other hand, with respect to the formation of the former (110) [001] grains, which are the cores of the favorable secondary recrystallized grains, warm rolling at 150 to 250 ° C. in final cold rolling, or 150 to 350 ° C. for 30 seconds. Although it is disclosed in Japanese Patent Publication No. 54-13846 and Japanese Patent Publication No. 54-29182 that the inter-pass aging at ˜10 hours is effective, this method alone is insufficient. This is because this method alone has a limit in the generation frequency of (110) [001] grains, and there are also excessive amounts of {111} <112> grains, which deviates from the (110) [001] orientation. This is because the primary recrystallized grains in the orientation also grow as secondary recrystallized grains, resulting in an increase in the ratio of secondary recrystallization inferior in orientation and a decrease in the magnetic flux density of the product.
[0010]
[Problems to be solved by the invention]
An object of the present invention is to solve the above-mentioned problem advantageously, and an object of the present invention is to propose a manufacturing method capable of stably obtaining a steel sheet having a higher magnetic flux density in a grain-oriented electrical steel sheet using AlN as an inhibitor. .
[0011]
In order to achieve this object, the invention in which the instability of magnetic flux density or the decrease in magnetic flux density of grain-oriented electrical steel sheets containing AlN as a main inhibitor is inherent in the method of precipitation dispersion of AlN in steel itself. Based on these new findings, we propose a new method for producing grain-oriented electrical steel sheets using the AlN precipitation dispersion control method.
[0012]
[Means for Solving the Problems]
  The gist configuration of the present invention is as follows.
(1) C is 0.10 wt% or less, Si is 2.5 to 5.0 wt%,Mn The 0.005 ~ 0.10wt %,A directional electrical steel slab containing 0.005-0.040 wt% Al and 0.0040-0.0130 wt% N, with the balance being composed of Fe and inevitable impurities, and the time from rough rolling start to finish rolling is less than 450 seconds After hot rolling is performed, hot-rolled sheet annealing is performed, and then the final sheet thickness is obtained by one or two cold rolling sandwiching intermediate annealing, followed by primary recrystallization annealing and secondary recrystallization annealing. In the manufacturing method of the grain-oriented electrical steel sheet to be applied,
  In the above hot rolling, the finish rolling start temperature is 1000 to 1230 ° C, the end temperature is 800 to 1100 ° C, and the cooling rate from the finish rolling to 700 ° C is 10 ° C / s or more. to take,
  The temperature rising rate between 600-800 ° C in the temperature rising process of the hot-rolled sheet annealing is 5-30 ° C / s, and the temperature of the hot-rolled sheet annealing and the annealing before the final cold rolling is 1125 ° C or less. To do,
  Adjusting the average grain size of the steel strip immediately before the final cold rolling to 10 to 35 μm; and
  Make the rolling reduction of the final cold rolling 80-95%
Characterized by the combination ofWhoA method for producing a grain-oriented electrical steel sheet (first invention).
[0013]
(2) In the first invention, the average grain size of the steel plate immediately before the final cold rolling is adjusted to 12.5 to 27.5 μm.WhoA method for producing a grain-oriented electrical steel sheet (second invention).
[0014]
(3) In the first invention or the second invention, the steel slab further comprises one or two of S and Se in a total amount of 0.005 to 0.030 wt.Including%Have
  It is characterized in that the start temperature of finish rolling in hot rolling is 1000 to 1200 ° C and the end temperature is 850 to 1000 ° C.WhoA method for producing a grain-oriented electrical steel sheet (third invention).
[0015]
(Four) C is 0.10 wt% or less, Si is 2.5 to 5.0 wt%,Mn The 0.005 ~ 0.10wt %,Containing 0.005-0.040 wt% of Al and 0.0040-0.0130 wt% of N, with the balance being a directional electrical steel slab with a composition of Fe and inevitable impurities, the time from the start of rough rolling to the end of finish rolling is 450 seconds or more After hot rolling is performed, hot-rolled sheet annealing is performed, and then the final sheet thickness is obtained by one or two cold rolling sandwiching intermediate annealing, followed by primary recrystallization annealing and secondary recrystallization annealing. In the manufacturing method of the grain-oriented electrical steel sheet to be applied,
  The steel slab is further 0.005-0.030 wt.Including%Have
  The time from the start to the end of finish rolling in the hot rolling is limited to 460 seconds or less, the finish rolling finish temperature is set to 850 to 1150 ° C, and the cooling rate from the finish rolling to 700 ° C is set to 10 ° C. Winding at 650 ° C or less as ℃ / s or more,
  The temperature rising rate between 600-800 ° C in the temperature rising process of the hot-rolled sheet annealing is 5-30 ° C / s, and the temperature of the hot-rolled sheet annealing and the annealing before the final cold rolling is 1125 ° C or less. To do,
  Adjusting the average grain size of the steel strip immediately before the final cold rolling to 10 to 35 μm; and
  Make the rolling reduction of the final cold rolling 80-95%
Characterized by the combination ofWhoA method for producing a grain-oriented electrical steel sheet (fourth invention).
[0016]
(Five) 1st invention-4th inventionEitherIn this, the steel slab further contains 0.005 to 0.060 wt% of Sb, the cooling rate in the hot-rolled sheet annealing step is 5 to 60 ° C./s, and at the time of temperature increase in the secondary recrystallization annealing, 800 to It is characterized in that it is maintained at a constant temperature for 15 to 60 hours at 890 ° C., or is heated or lowered at a temperature rising rate or a temperature falling rate of 5 ° C./hr or less within this temperature range.WhoA method for producing a grain-oriented electrical steel sheet (fifth invention).
(6) In any one of 1st invention-5th invention, steel slab is further Cu The 0.005 ~ 0.30wt % Content-containing electrical steel sheet manufacturing method (6th invention) characterized by the above-mentioned.
(7) 1st invention-1st6inventionEitherIn the steel slab, one or two selected from Sn, P, Bi, As, B, Ge, V, Nb, Cr and Te are used, and Sn and Cr are 0.03 to 0.30 wt%, Bi respectively. Is 0.005 to 0.020 wt%, P, Ge, V, Nb, As, and Te are 0.005 to 0.030 wt%, and B is 0.0005 to 0.0020 wt%.WhoProduction method of grain-oriented electrical steel sheets (No.7invention).
(8) 1st invention-1st7inventionEitherThe steel slab further contains 0.005 to 0.020 wt% of Mo.WhoProduction method of grain-oriented electrical steel sheets (No.8invention).
[0017]
The “steel strip immediately before the final cold rolling” in the present invention means that after the cold rolling method is performed, hot-rolled sheet annealing is performed, and in the case of the cold rolling method, intermediate annealing is performed. It means the steel strip before the final cold rolling.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Now, the inventors have conducted extensive research to solve the problems of the prior art with the primary viewpoint of controlling the primary recrystallized grains to a suitable texture as described above. It has been found that increasing the grain size of the immediately preceding steel strip is particularly effective. That is, when the grain size of the steel strip immediately before the final cold rolling is controlled within a specific range, (110) [001] grains increase as the primary recrystallization texture after rolling and recrystallization, and { 111} <112> grains were found to decrease to an appropriate amount.
[0019]
By applying this method to the final cold rolling during the manufacturing process of the Al-containing grain-oriented electrical steel sheet in which the rolling reduction is 80% or higher, it becomes possible to appropriately control the primary recrystallization texture. . However, this new method cannot be directly applied to the conventional technology.
[0020]
This is because in the conventional method for producing an Al-containing grain-oriented electrical steel sheet, as disclosed in Japanese Patent Publication Nos. 46-23820 and 62-56923, annealing before the final cold rolling is an inhibitor. Therefore, the temperature and cooling rate during the annealing are determined by the finely dispersed precipitation conditions of the above AlN in the steel. This is because the annealing conditions cannot be optimized independently of the finely dispersed precipitation conditions of AlN for controlling the texture as described above.
[0021]
More specifically, in the conventional inhibitor control technology for Al-containing grain-oriented electrical steel sheets disclosed in Japanese Patent Publication No. 46-23820 and Japanese Patent Publication No. 62-56923, the AlN is uniformly finely dispersed and precipitated. In addition, AlN is solid-dissolved by heat treatment at a high temperature, and then a uniform fine dispersion state preferable as an inhibitor is caused by rapid cooling. However, in such a high temperature treatment, the crystal grains of the steel sheet surface layer portion having a complete α structure become excessively coarse, and the {111} <112> grains of the steel sheet surface layer portion become extremely large in the primary recrystallization annealing after the final cold rolling. The phenomenon is that the growth of (110) [001] grains during secondary recrystallization annealing is inhibited and secondary recrystallization failure is frequently caused. Therefore, it is not always appropriate from the viewpoint of control of the texture. I couldn't.
[0022]
In addition, since AlN dissociated and dissolved at high temperature and precipitated during cooling is metastable, it tends to grow Ostwald and lose its restraining force during final finish annealing. There was a problem that it was easy to induce crystal defects.
[0023]
The instability of the magnetic properties of the Al-containing grain-oriented electrical steel sheet is caused by such a phenomenon, and the nitriding treatment described in the prior art is a means applied to prevent the above-described loss of inhibitory inhibitory power. It is. However, since this nitriding treatment is a technique that generally promotes the growth of secondary recrystallization nuclei, it also causes the growth of secondary recrystallization nuclei with poor orientation. It will cause a decline.
[0024]
As described above, it can be said that all problems are caused by the drawback that the control of the inhibitor and the control of the texture cannot be performed independently in the conventional technique.
[0025]
In addition to the problems described so far, there has also been a problem of deterioration of magnetic properties due to the form of hot rolling. That is, hot rolling is usually performed by an arrangement of a plurality of hot rolling mills divided into rough rolling and finish rolling. This rough rolling is rolling in which the time interval between rollings has sufficient time to cause static recrystallization or static recovery, while finish rolling is achieved by a short interval arrangement (tandem rolling mill) of rolling mills. Apart from dynamic recrystallization and dynamic recovery effects, this is rolling in which distortion during rolling is additionally imparted to the steel.
[0026]
Here, hot rolling of Al-containing grain-oriented electrical steel sheets requires processing in a shorter time than hot rolling of normal grain-oriented electrical steel sheets in order to avoid coarse precipitation of AlN. In the technique disclosed in Japanese Patent Publication No. 51-2290, the time from the slab heating extraction to the temperature drop from 1000 to 1250 ° C. is set to 200 seconds or less, and the time from the time to the temperature drop to 600 ° C. is set to 200 seconds or less. It is said that it is necessary to control the cooling to the end and finish the hot rolling process during this period.
[0027]
However, along with the increase in production of grain-oriented electrical steel sheets, it is necessary to carry out hot rolling of grain-oriented electrical steel sheets with excellent characteristics even in long hot rolling mills that require a long time for hot rolling. It has become. For example, in a hot rolling factory that performs mixed rolling with other steel types, the distance from the roughing mill to the finish rolling mill is long, and therefore it is often necessary to set the time from the start of rough rolling to the end of finish rolling to less than 400 seconds. With difficulty. In addition, a method of performing reciprocal rolling in a single rolling mill (for example, a stickel mill) a plurality of times as finish rolling after rough rolling, and coiling winding between the passes is inevitably hot rolling. Therefore, these hot rolling methods could not stably produce a grain-oriented electrical steel sheet having excellent magnetic properties.
[0028]
In this regard, in the method for producing a grain-oriented electrical steel sheet according to the present invention, a grain-oriented electrical steel sheet having excellent magnetic properties can be produced even in such a special hot rolling form.
[0029]
Inconvenience inevitably accompanied by precipitation annealing as described above, that is, by performing inhibitor precipitation dispersion control and primary recrystallization texture control in the same annealing, the problem that it is difficult to optimize each control is solved, Inhibitor dispersion precipitation control and primary recrystallization texture control can be performed independently, and even in long hot rolling mills where hot rolling requires a long time, directional electromagnetic An epoch-making technique capable of obtaining a steel sheet is proposed by the present invention.
[0030]
That is, the present invention has been completed as a result of research and development based on the following four new findings.
(1) By controlling the various hot rolling conditions, the dispersion state of precipitation of AlN in the subsequent process can be controlled.
(2) AlN is sufficiently precipitated during the heating process up to 1000 ° C in hot-rolled sheet annealing, and its precipitation dispersion state can be controlled at a heating rate between 600-800 ° C.
(3) Annealing before the final cold rolling (one cold rolling method is equivalent to hot-rolled sheet annealing and two-time cold rolling method is intermediate annealing) in order to sufficiently avoid AlN re-solution or Ostwald growth. , Keep the temperature below 1125 ℃,
(4) As the primary recrystallization texture, there is an appropriate range for the density of {111} <112> grains, and the control thereof controls the average crystal grain size of the steel sheet immediately before the final cold rolling to an appropriate value of 10 to 35 μm. (That is, it is performed by appropriately controlling the soaking temperature and soaking time of the annealing before the final cold rolling.)
[0031]
In the following, experiments that have motivated the present invention to be completed will be described.
C: 0.075 wt% (hereinafter, simply referred to as “%”), Si: 3.34%, Mn: 0.069%, P: 0.007%, S: 0.003%, Al: 0.025%, Se: 0.019%, Mo: 0.012 % And N: 0.0085% of three steel slabs were heated at 1420 ° C. for 15 minutes soaking and then hot rolled for 220 to 280 seconds to obtain a hot rolled sheet having a thickness of 2.2 mm. At this time, after the rough rolling, one slab has a finishing rolling start temperature of 1100 to 1180 ° C. and a finishing rolling finishing temperature of 870 to 920 ° C., and the cooling rate from the finish rolling to coil winding is set. The water was quenched at 16 ° C./s with jet water and wound up at 550 ° C. (condition a).
[0032]
Among the other two, one slab was wound at 650 ° C. with the hot rolling finish rolling conditions the same as the condition a, the cooling rate after finish rolling was 8 ° C./s. Condition b).
For the remaining one, after the rough rolling, the finish rolling start temperature is set to 1270 to 1290 ° C., the finish rolling end temperature is set to 1150 to 1180 ° C., the cooling rate after finish rolling is gradually cooled to 8 ° C./s, 550 It wound up at the temperature of (degree C) (condition c).
[0033]
Each of these coils is divided into 12 parts,₁~ A₁₂, B₁~ B₁₂, C₁~ C₁₂The hot-rolled sheet annealing for 1 minute was performed at 1000 degreeC.
At this time, the symbol a₁, A_Four, A₇, A_Ten, B₁, B_Four, B₇, B_Ten, C₁, C_Four, C₇And c_TenFor, rapid heating was performed at a rate of temperature increase of 45 ° C./s. The symbol a₂, A_Five, A₈, A₁₁, B₂, B_Five, B₈, B₁₁, C₂, C_Five, C₈And c₁₁As for, the heating rate was controlled to 12 ° C./s. Furthermore, the symbol a_Three, A₆, A₉, A₁₂, B_Three, B₆, B₉, B₁₂, C_Three, C₆, C₉And c₁₂As for, the temperature rising rate was gradually cooled at 3 ° C./s.
[0034]
These steel sheets were pickled, made 1.50 mm thick by cold rolling, and then subjected to intermediate annealing. As the conditions for this intermediate annealing, a₁, A₂, A_Three, B₁, B₂, B_Three, C₁, C₂And c_ThreeAs for, after soaking at 1050 ° C. for 60 seconds, it was quenched with mist water. a_Four, A_Five, A₆, B_Four, B_Five, B₆, C_Four, C_FiveAnd c₆As for, after soaking at 1050 ° C. for 100 seconds, it was quenched with mist water. a_Ten, A₁₁, A₁₂, B_Ten, B₁₁, B₁₂, C_Ten, C₁₁And c₁₂As for, after soaking at 1150 ° C. for 60 seconds, it was quenched with mist water.
[0035]
These steel sheets were finished to a final sheet thickness of 0.19 mm by warm rolling at 150 to 230 ° C. after pickling. After this, decarburization and primary recrystallization annealing were performed, and an annealing separator was applied and wound into a coil shape. The conditions for this decarburization and primary recrystallization annealing were as follows: Dew point 60 ℃, H₂55%, balance N₂The atmosphere was balanced. Also, the annealing separator is 10% TiO₂And 3% Sr (OH)₂・ 8H₂MgO containing O is applied to both sides of the coil.
[0036]
After this, final finish annealing was performed for the purpose of secondary recrystallization annealing and purification annealing.₂Heated up in the atmosphere, 25% N from 850 ° C to 1160 ° C₂And 75% H₂In a mixed atmosphere with a temperature rising rate of 12 ° C./hr.₂The temperature was lowered after holding at 1160 ° C. for 5 hours.
[0037]
After the final finish annealing, after removing the unreacted annealing separator, apply a tension coating mainly composed of magnesium phosphate and colloidal silica, and then apply a coating heat treatment at 800 ° C for 1 minute to double the planarization annealing. Thereafter, a magnetic domain fragmentation treatment was performed by plasma jet irradiation to obtain a product.
Table 1 shows the magnetic characteristics of each product coil.
[0038]
[Table 1]

[0039]
As shown in Table 1, the most excellent magnetic properties are the steel sheet of hot rolling condition a, the heating rate of hot-rolled sheet annealing is controlled to 12 ° C / s, and the soaking condition of intermediate annealing is 1050 ° C. It is obtained when it is set to 100 seconds.
[0040]
Here, in order to investigate the reason why such excellent results were obtained, hot-rolled sheets having hot rolling conditions a, b and c were changed up to 1000 ° C. by changing the heating rate in three stages according to the experiment. Table 2 shows the observation results of the precipitates in the steel with an electron microscope for the steel plates rapidly cooled after the temperature was raised.
[0041]
[Table 2]

[0042]
As shown in Table 2, under conditions with the most excellent magnetic properties (hot rolling condition a, hot rolled sheet annealing conditions 2, 5, and 8 (12 ° C./s)), 1000 of hot rolled sheet annealing was achieved. It can be seen that the MnSe-AlN composite precipitates having a fine size of 5 to 10 nm are already deposited at an extremely high density in the temperature raising process up to 0 ° C. Since this composite precipitate is not observed at the stage of hot-rolled sheet, it is clear that it was generated in the temperature rising process of hot-rolled sheet annealing. The density at which this product precipitates was found to depend on the hot rolling conditions and the rate of temperature increase between 600 and 800 ° C. during hot-rolled sheet annealing, as a result of subsequent detailed investigations. That is, when the rate of temperature increase between 600 and 800 ° C. in the hot-rolled sheet annealing is less than 5 ° C./s, the precipitation frequency of precipitation nuclei decreases and the size of the precipitates increases. Conversely, when the rate of temperature rise exceeds 30 ° C./s, it precipitates finely and with high density, but does not achieve a uniform dispersion state. According to another investigation, the hot rolling conditions are preferably low enough not to precipitate AlN, that is, extremely fine stacking faults, precipitates, and interpositions introduced by hot rolling at low temperatures. It was found that the product becomes a fine AlN precipitation site.
[0043]
Incidentally, in the case of this experiment containing Mn and Se, very fine MnSe precipitates during the finish rolling of hot rolling, and this becomes a fine AlN precipitation site, resulting in a fine MnSe-AlN composite precipitate of 5 to 10 nm. Is generated. Note that the fine AlN generated during the temperature rise of hot-rolled sheet annealing is a crystalline precipitate having a hexagonal Wurtzite (ZnS) structure, and may have some Si depending on the temperature-rise rate of hot-rolled sheet annealing. However, since the effect of the restraining force is determined only by the particle size, it may be handled equally.
[0044]
In the above hot rolling, in order to form a large number of such AlN precipitation sites, when the hot rolling time of less than 450 seconds is used as the time from the start of rough rolling to the end of finish rolling, finish rolling is performed at a lower temperature than conventional. It is good to carry out, and it is necessary to set the finish rolling start temperature to 1000-1230 ° C and the end temperature to 800-1100 ° C. By such temperature control, extremely fine stacking faults, inclusions or precipitates are generated. The frequency will increase, and it will be possible to provide fine AlN precipitation sites in the temperature rising process of hot-rolled sheet annealing. When the finish rolling temperature is higher than the above temperature, the precipitation sites of fine AlN are insufficient, and as shown in the column of hot rolling conditions c in Table 2, AlN newly precipitated during the temperature rising process of hot rolled sheet annealing. And the size increases, and a good suppressive force as an inhibitor cannot be obtained.
[0045]
  In order to increase the AlN precipitation sites with certainty, it is a good method to add S or / and Se to the steel and obtain these ultrafine crystals by hot rolling. For this purpose, one or two of S and Se are contained in a total amount of 0.005 to 0.30%.Let, Sulfides and / or selenides are formed by hot rolling. The hot rolling conditions suitable for ultrafine precipitation of such precipitates are 1000 to 1200 ° C. as the finish rolling start temperature and 850 to 1000 ° C. as the end temperature.
[0046]
However, when Se is contained in the steel, it is possible to precipitate ultrafine selenide in the steel by hot rolling at the lowest temperature for a long time, so finish rolling from the start of hot rolling rough rolling. The present invention can also be applied to special hot rolling in which the time until completion is 450 seconds or more.
[0047]
That is, in hot rolling of steel containing 0.005 to 0.030% of Se in steel, the time from the start to the end of finish rolling of hot rolling is set to 460 seconds or less, and the hot rolling end temperature is set to 850 to 1150 ° C. By doing so, it is possible to deposit a very fine selenide which becomes a precipitation site of fine AlN deposited in the temperature rising process of hot-rolled sheet annealing at a high density. At this time, if the hot rolling end temperature exceeds 1150 ° C or the time from the start to the end of finish rolling exceeds 460 seconds, the selenide precipitated by hot rolling is only coarse, and conversely, hot rolling When the end temperature is less than 850 ° C., the precipitation frequency of the ultrafine selenide decreases, and in any case, the fine AlN precipitated in the temperature rising process of hot-rolled sheet annealing does not have a high density distribution.
[0048]
Next, the results of detailed investigation on the difference between the hot rolling conditions a and b in Table 2 will be described. When the cooling rate of the steel sheet after hot rolling is low, a stable precipitation state of Si-rich Al / Si composite nitride (Si, Al) N occurs. This composite nitride is a crystalline precipitate (hexagonal Wurtzite structure), is relatively thermally stable, and is coarse as observed in the hot-rolled sheet under the hot-rolling condition b shown in Table 2. A precipitate forms a composite precipitate with MnSe or produces a petal-like precipitate alone. This precipitate is AlN (Si diffuses into the steel during the temperature rising process of hot-rolled sheet annealing, conversely, Al penetrates, Si and Al are substituted, and Al-rich (Al , Si) N is finally converted to AlN.), But the size is almost maintained after hot-rolled sheet annealing.
[0049]
Such Si-rich Al and Si complex nitrides are observed even when the coil winding temperature after hot rolling is high, and the amount and frequency of fine AlN deposited during the temperature rising process of hot-rolled sheet annealing. Is a particularly harmful precipitate.
[0050]
Incidentally, indefinite type (Si, Al) N is recognized in the hot-rolled sheets of Table 2 hot-rolled conditions a and c that are rapidly cooled after completion of hot rolling and coiled at a low temperature. Crystalline (Si, Al) N is hardly observed. In addition, this amorphous (Si, Al) N is a metastable amorphous material formed by rapid cooling, and is considered to decompose and re-solidify easily at the initial stage of the temperature rising process of hot-rolled sheet annealing. Specifically, this nitride may be handled as being in the form of a solid solution.
[0051]
Measure the amount of nitride precipitation in the hot rolled sheet and the steel sheet immediately after the temperature rise of 1000 ° C. in the temperature rising process shown in Table 2, and determine the degree of precipitation as (N as nitride) ÷ (total N) When calculated and evaluated by value, in the case of hot-rolling condition a, 0.42 for hot-rolled sheet and 0.95 immediately after heating at 1000 ° C. for hot-rolled sheet, whereas in the case of hot-rolling condition b, 0.84 for hot-rolled sheet, Hot-rolled sheet annealing was 0.98 immediately after the temperature rise of 1000 ° C, and a large amount of nitride had already precipitated after the hot rolling process was completed, and the amount of AlN newly precipitated during the hot-rolled sheet annealing process was extremely high. I understand that there are few.
[0052]
In order to suppress the precipitation of crystalline (Si, Al) N, which is harmful because it is coarse and stable as described above, the steel plate is cooled to 700 ° C after hot rolling. It is necessary to avoid the long-term residence in the precipitation temperature region of crystalline (Si, Al) N by setting the speed to 10 ° C./s or more and the coil winding temperature to 650 ° C. or less.
[0053]
Next, in the present invention, in addition to the first requirement relating to the hot rolling conditions, as a second requirement, in order to effectively utilize the fine AlN generated in the temperature rising process of the hot rolled sheet annealing, In addition, in addition to this, in the two cold rolling methods, it is necessary to set the maximum annealing temperature to 1125 ° C. or less, including intermediate annealing.
[0054]
In the experiment, under the hot rolling condition a shown in Table 1 and when the heating rate of hot-rolled sheet annealing is 12 ° C / s, and the soaking temperature of intermediate annealing is 1050 ° C, the magnetic properties are extremely excellent. A product was obtained, but when the soaking temperature was increased to 1150 ° C, the magnetic properties deteriorated significantly.
[0055]
In order to investigate this reason, the change in the precipitation particle size distribution of the inhibitor was examined, and the inhibitory power was investigated. FIG. 1 shows a hot-rolled sheet when the temperature increase rate of hot-rolled sheet annealing is 12 ° C./s and the intermediate annealing condition is 1050 ° C. for 100 seconds under the hot rolling condition a. 2 shows the measurement results of the particle size distribution of the steel plate immediately after the temperature rise of 1000 ° C. and the precipitate after decarburization and primary recrystallization annealing in hot rolled sheet annealing. On the other hand, FIG. 2 shows the case where the temperature increase rate of hot-rolled sheet annealing is 12 ° C./s and the intermediate annealing condition is 1150 ° C. for 60 seconds under the hot rolling condition c, that is, precipitates of each steel plate in the conventional method. The measurement result of the particle size distribution is shown. In addition, since many fine carbide precipitates in the steel plate after intermediate annealing here, and it is difficult to distinguish from the precipitate which is an inhibitor, it does not show in the figure.
[0056]
As shown in FIG. 1, in the method of the present invention, a large number of fine precipitates having a size of 50 to 100 mm are precipitated by the temperature increase up to 1000 ° C. in the hot-rolled sheet annealing. It is maintained almost unchanged after crystal annealing.
[0057]
On the other hand, in the conventional method shown in FIG. 2, the amount of fine precipitates does not increase so much by hot-rolled sheet annealing, and the steel sheet after decarburization and primary recrystallization annealing is 100 to 200 mm for the first time. The size of fine precipitates is increasing. In more detail, the precipitation time and changes of fine precipitates in this case were partially investigated during cooling of hot-rolled sheet annealing, and slightly coarsened by Ostwald growth in the α phase at high temperatures of intermediate annealing. The remainder was a solid solution in the γ phase at the high temperature of intermediate annealing and reprecipitated during cooling. In this way, the grain size distribution of the inhibitor is controlled by the Ostwald growth and the solid solution / recrystallization process in the intermediate annealing, so it is less affected by the previous process such as hot rolling and hot rolled sheet annealing. A stable particle size distribution is obtained.
[0058]
However, the size of the precipitate is slightly larger than the method of the present invention and is not a satisfactory size. In contrast, in the method of the present invention, it was possible to obtain extremely fine precipitates having a size of 50 to 100 mm by strictly controlling the hot rolling conditions and the hot rolled sheet annealing conditions. This means that it is possible to control the precipitation of an inhibitor having an extremely strong inhibitory force.
[0059]
Furthermore, following this investigation, the cause of the deterioration of the magnetic properties at the above-mentioned intermediate annealing temperature of 1150 ° C. was investigated. As a result, it was found that 50 to 100 Å precipitates were coarsened due to Ostwald growth. In order to suppress the growth, it was found that the intermediate annealing temperature must be regulated to 1125 ° C or lower.
[0060]
Therefore, in both methods, there are various advantages and disadvantages, but as long as attention is paid to the hot rolling conditions, the heating rate of hot-rolled sheet annealing, and the maximum temperature regulation of the cold rolling process, the method of the present invention is used. There is an advantage that a product having extremely excellent magnetic properties can be obtained.
[0061]
Next, control of the texture that is the third requirement of the present invention will be described.
In the hot rolling condition a of Table 1, in the column of the heating rate of hot rolled sheet annealing of 12 ° C / s, as the intermediate annealing conditions, the soaking temperature: 1050 ° C, time: 60 seconds, and 100 seconds are compared. The treatment for 100 seconds is markedly superior in both magnetic flux density and iron loss. When this cause was investigated in detail, there was no significant difference in the precipitation state of fine AlN between the two. However, when the decarburization and primary recrystallization textures were compared, the sample (a_Five), Soaking time: 60 second sample (a₂), The density of (110) [001] grains increased about 1.5 times, and the density of {111} <112> grains was reduced 0.8 times. This increase in (110) [001] grains increases the probability that crystal grains with better orientation will be the nucleus of secondary recrystallization, and the decrease in density of {111} <112> grains results in crystal grains with poor orientation. Is suppressed to become the nucleus of secondary recrystallization, and finally helps to improve the orientation of secondary recrystallization grains.
[0062]
In pursuit of the cause of this decarburization / primary recrystallization texture change, the average grain size after intermediate annealing increased from 5 μm to 18 μm due to an increase in soaking time. all right.
[0063]
It has been known that the crystal grain size immediately before the final cold rolling has a large effect on the primary recrystallization texture in this way, but in the conventional manufacturing method, intermediate annealing or hot-rolled sheet annealing is used. Since the temperature is high, if the soaking temperature is changed to change the crystal grain size, the inhibitor's inhibitory force also changes, so the inhibitor's inhibitory force is maintained during intermediate annealing and hot-rolled sheet annealing. The crystal grain size immediately before the final cold rolling could not be independently controlled within the proper range.
[0064]
In contrast, in annealing at a low temperature of 1125 ° C. or lower according to the present invention, the crystal grain size can be changed without changing the precipitation state of the inhibitor, and this is the first time to control to an appropriate primary recrystallization texture. It is now possible to do. The appropriate average crystal grain size before the final cold rolling is 10 to 35 μm, more preferably 12.5 to 27.5 μm. These average crystal grain sizes are the steel composition, annealing temperature, annealing time. It can be adjusted by changing the annealing atmosphere.
[0065]
Regarding the texture control method, there are conventionally known methods, such as warm rolling at 150 to 250 ° C., low temperature during cooling of annealing before pass aging and final cold rolling. A technique for controlling carbide precipitation or precipitate size by holding is mentioned, and the effect is further enhanced by combining with the method of the present invention.
[0066]
Finally, in the Al-containing grain-oriented electrical steel sheet, in order to increase the formation frequency of {111} <112> grains and the formation frequency of (110) [001] grains, the reduction ratio of the final cold rolling is known as known in the art. It is necessary to make it 80 to 95%, and if it is out of this range, the formation frequency of {111} <112> grains is drastically lowered, resulting in deterioration of magnetic properties.
[0067]
Further, in order to improve the magnetic properties of the grain-oriented electrical steel sheet according to the present invention, Sb in the steel is added as is well known, and secondary recrystallization is performed by utilizing the segregation effect on the grain boundaries and surface of this Sb. For this purpose, it is effective to maintain a constant temperature between 800 to 890 ° C. for 15 to 60 hours at the time of temperature increase of the secondary recrystallization annealing, or to increase the temperature to 5 ° C./hr or less. The temperature is increased or decreased at a temperature rate or a temperature decrease rate. Thereby, the crystal orientation of secondary recrystallization can be made sharper.
[0068]
Hereinafter, the components of the grain-oriented electrical steel slab as a starting material of the present invention will be described.
[C: 0.10% or less]
C is necessary to improve the hot-rolled structure by using the γ transformation, but in some cases, it may be produced without performing a decarburization step, and an appropriate amount is contained in consideration of these. On the other hand, if it exceeds 0.10%, decarburization will be poor, so 0.10% or less.
[0069]
[Si: 2.5-5.0%]
  Si needs to be 2.5% or more in order to increase electric resistance and improve iron loss. On the other hand, if it exceeds 5.0%, embrittlement is severe and cold rolling becomes difficult, so the range is from 2.5 to 5.0%.
[ Mn : 0.005 ~ 0.10 %]
  Mn Is useful for preventing cracking during hot rolling, MnS And MnSe When a secondary inhibitor such as is used, it is also useful as an inhibitor-forming component. To this end 0.005 % Or more is necessary, and the upper limit is to form a secondary inhibitor. 0.10 Up to%. That is, 0.10 If it exceeds 50%, it becomes coarse as a precipitate, the inhibitory power as an inhibitor is lowered, and the magnetic properties are deteriorated.
[0070]
[Al: 0.005 to 0.04%]
Al is a basic component for precipitating AlN, which is an essential main inhibitor for obtaining a grain-oriented electrical steel sheet having a high magnetic flux density as expected in the present invention. If it is less than 0.005%, the amount of AlN deposited is sufficient. On the other hand, if it exceeds 0.04%, the precipitated AlN coarsens and the suppressive force deteriorates, so the range is 0.005 to 0.04%.
[0071]
[N: 0.0040-0.0130%]
N is also a basic component for precipitating AlN, which is an essential main inhibitor in order to obtain a high magnetic flux density grain-oriented electrical steel sheet as intended in the present invention. This N is not necessarily required to contain a predetermined amount in the steel slab and can be replenished by nitriding during the manufacturing process.0.0040If it is less than%, the amount of AlN is insufficient in this invention. Conversely, if it exceeds 0.0130%, it will gasify when heating the steel slab, causing troubles such as blistering. Therefore, the range is 0.0040 to 0.0130%.
[0072]
  As mentioned above, C, Si,Mn ,Al and N are essential components for the present invention, and other components may be essentially Fe except for impurities.
  However, in order to enhance the effects of the present invention, it is possible to further contain the following known components.
[0074]
Cu is a useful component because it forms sulfides, selenides, etc., but 0.005% or more is necessary for this purpose. However, if it exceeds 0.30%, it becomes coarse as a precipitate, and the inhibitory power as an inhibitor is reduced, and its effectiveness is lost.
[0075]
S and Se are useful components because they bind to Mn or Cu to precipitate MnS, MnSe, CuS and CuSe as auxiliary inhibitors. In order to bring about this effect, 0.005% or more in total is necessary. On the other hand, if it exceeds 0.030%, the precipitates become coarse and the magnetic properties are deteriorated, so the range of 0.005 to 0.030% preferable.
[0076]
Sb is an effective component because it suppresses oxidation and nitridation of the surface layer portion of the steel sheet and enhances the selectivity of the nucleus in secondary recrystallization annealing, and has the effect of segregating at the crystal grain boundary and reinforcing the suppression force. For these effects, a content of 0.005% or more is necessary. However, if it exceeds 0.060%, the steel sheet becomes brittle, so a range of 0.005 to 0.060% is preferable.
[0077]
Furthermore, it is a matter of course that Sn, P, Bi, As, B, Ge, V, Nb, Cr, Te, etc., which are known as inhibitor reinforcing components, may be contained. For this purpose, Sn and Cr are contained in the range of 0.03 to 0.30%, Bi is 0.005 to 0.020%, P, Ge, V, Nb, As and Te are contained in the range of 0.005 to 0.030%, and B is contained in the range of 0.0005 to 0.0020%. Is preferred.
In addition, it is possible to contain 0.005 to 0.020% of Mo in order to prevent cracking in hot rolling that is characteristic of grain-oriented electrical steel.
[0078]
Next, the requirements for the manufacturing process in the present invention will be described.
The grain-oriented electrical steel containing the above components is made into a hot-rolled steel strip by hot rolling. At this time, when a secondary inhibitor component such as S or Se is contained, high temperature slab heating is performed. However, when only AlN is used as an inhibitor, normal slab heating around 1200 ° C. or high temperature slab after continuous casting is applied. Direct rolling is also possible.
[0079]
Here, in hot rolling consisting of rough rolling and finish rolling, in the case of hot rolling of ordinary directional electrical steel consisting of less than 450 seconds as the time from the start of rough rolling to the end of finish rolling, The start temperature of finish rolling is set to 1000 to 1230 ° C, and the end temperature is set to 800 to 1100 ° C. By adjusting to this temperature range, it is possible to deposit and disperse AlN at a high density, and as a result, a product having excellent magnetic properties can be obtained. The reason for this has not been completely elucidated yet, but by finishing rolling in such a temperature range, extremely fine stacking faults, sulfides, selenides, and oxides are formed at high density, and hot rolling in the next step is performed. It is estimated that the fine AlN precipitation sites that precipitate during the temperature increase process during plate annealing will be sufficiently formed.
[0080]
Here, when the finish rolling temperature is higher than this range, the amount of fine AlN precipitation sites formed is not sufficient, the precipitated AlN coarsens, and the precipitation frequency also decreases. The magnetic properties of are deteriorated. In addition, even when the finish rolling temperature is lower than this range, the amount of precipitation sites formed becomes insufficient, and the AlN precipitated during the temperature rising process of hot-rolled sheet annealing becomes coarse, resulting in a reduction in restraining force, The magnetic properties of are deteriorated.
[0081]
  Also, S and / or Se alignment in steelIn CuIn the case of containing Ni, the precipitates of ultrafine CuS, CuSe, MnS or MnSe are more clearly formed, which contributes particularly effectively as fine AlN precipitation sites that precipitate in the temperature rising process of hot-rolled sheet annealing. At this time, in order to express this effect remarkably, it is preferable that the start temperature of finish rolling of hot rolling is 1000 to 1200 ° C. and the end temperature is 850 to 1000 ° C. The reason for limiting the temperature is the same as described above.
[0082]
On the other hand, even in the case of hot rolling in which the time from the start of rough rolling to the end of finishing rolling is 450 seconds or more due to the long rolling mill arrangement or the reverse of the finishing mill. Is extremely effective. At this time, it is necessary to contain Se in the steel. The reason is that by adding Se, Cu_xSe and MnSe precipitate, but this Cu_xThis is because Se and MnSe have a low precipitation temperature and a slow diffusion rate of Se, so that a very fine precipitate can be sufficiently obtained even in hot rolling at a low temperature for a long time.
[0083]
Appropriate conditions for hot rolling in such a case are that the time from the start to the end of finish rolling of hot rolling should be 460 seconds or less, and the finish rolling finish temperature should be 850 to 1150 ° C. It is presumed that fine AlN precipitation sites that precipitate in the temperature rising process of hot-rolled sheet annealing in the next process are sufficiently formed.
[0084]
If the time from the start to the end of finish rolling exceeds 460 seconds or the end temperature of hot rolling is out of the temperature range of 850 to 1150 ° C, even with the method of the present invention, coarse Cu is used._xPrecipitation of coarse crystalline AlN compound-deposited on Se and MnSe cannot be suppressed, resulting in coarsening of AlN, and thus there is no effect of improving the inhibitor's inhibitory force, resulting in deterioration of the magnetic properties of the product.
[0085]
Next, after the hot rolling is completed, it is necessary to set the cooling rate to 700 ° C. to 10 ° C./s or more and the coil winding temperature to 650 ° C. or less by rapid cooling of the steel sheet. This condition is the same whether the time from the start of rough rolling to the end of finish rolling is less than 450 seconds or more than 450 seconds during hot rolling.
[0086]
This rapid cooling and low-temperature winding treatment prevents the formation of harmful crystalline (Si, Al) N in the steel, and newly adds fine AlN in the temperature rising process of the next hot-rolled sheet annealing. Thus, the inhibitory power of the inhibitor AlN can be improved.
[0087]
Conversely, if the cooling rate to 700 ° C is less than 10 ° C / s, or if the coil winding temperature exceeds 650 ° C, it is long in the precipitation temperature region of thermally stable crystalline (Si, Al) N. Since it stays for a long time, the amount of fine AlN newly precipitated in the temperature rising process of hot-rolled sheet annealing is insufficient, and the inhibitory power of the inhibitor AlN cannot be improved, and the magnetic properties deteriorate. The crystalline (Si, Al) N deposited here is replaced with Si and Al in the subsequent steps and ultimately converted into AlN, but its size does not change roughly. The coarse size deposited at the beginning is stored until the end, and does not contribute to the improvement of the inhibitor inhibitory power.
[0088]
The steel sheet after hot rolling is subjected to hot-rolled sheet annealing, and the final sheet thickness is obtained by cold rolling twice or once with intermediate annealing.
Here, the temperature rising process of the hot-rolled sheet annealing is one of the most important processes in the present invention, and it is important to set the temperature rising rate at 600 to 800 ° C. to 5 to 30 ° C./s. By controlling the heating rate, fine AlN is formed at a high density on the AlN precipitation sites generated in a large amount in the hot rolling stage. The fine AlN begins to be deposited at around 600 ° C, and most of it precipitates at around 800 ° C. Therefore, the rate of temperature rise in this temperature range is important.
[0089]
Here, when the rate of temperature rise in this temperature range exceeds 30 ° C / s, AlN precipitates densely and finely at the precipitation site, but depending on the location in the steel, there is a region with insufficient precipitation density. However, it does not result in uniform fine and high density precipitation. On the other hand, when the rate of temperature increase is less than 5 ° C./s, the precipitation frequency decreases and the size of the precipitate increases. As described above, when the temperature rising rate of 600 to 800 ° C. is out of the range of the present invention, the inhibitor inhibitory power is lowered, so that the magnetic properties of the product are deteriorated.
[0090]
From the above, the dispersion control of the size, precipitation frequency, and uniformity of fine AlN precipitation, which is the main inhibitor of the present invention, is controlled by the temperature increase rate at 600 to 800 ° C. in the temperature increase process of such hot-rolled sheet annealing. It can be said that it is made by control.
[0091]
The fine AlN dispersed and precipitated by controlling the heating rate is highly likely to deteriorate in the dispersed state due to Ostwald growth or solid solution / reprecipitation during annealing immediately before cold rolling. It is particularly important that the upper limit of the temperature is 1125 ° C. or lower. In other words, in normal annealing at high temperatures such as 1150 ° C and 1200 ° C, AlN Ostwald growth (α-Fe portion) and solid solution / recrystallization (γ-Fe portion) The purpose is to obtain a suitable dispersed precipitation state, but this method is inferior to the method of the present invention as a method of fine and uniform dispersion of AlN as shown by the experimental results described above. Therefore, it is impossible to obtain a strong suppression effect as in the present invention. Therefore, the maximum temperature of the hot rolled sheet annealing and the annealing before the final cold rolling in the present invention is 1125 ° C.
[0092]
Further, the lower limit of the annealing temperature is not particularly defined. However, as shown in the viewpoints of precipitation control at the time of increasing the temperature of AlN and the examples, the average grain size control immediately before the final cold rolling is also 1000%. It is desirable to exceed ℃.
[0093]
Furthermore, as a third technique of the present invention, the primary recrystallization texture may be controlled by controlling the average crystal grain size of the steel sheet immediately before the final cold rolling. That is, it is necessary to control the average crystal grain size of the steel sheet before the final cold rolling to 10 to 35 μm, and more preferably to 12.5 to 27.5 μm.
Thus, by adjusting the steel plate grain size immediately before the final cold rolling to a range of 10 to 35 μm, the generation frequency of (110) [001] grains is increased and the generation frequency of {111} <112> grains is increased. In other words, the growth of the secondary recrystallized grains as the secondary recrystallized grains in the orientation deviated from the (110) [001] orientation is suppressed, and the (110) [001] of the secondary recrystallized grains of the product is suppressed. The accumulation in the orientation can be increased, and the magnetic characteristics can be further improved.
[0094]
Here, when the average crystal grain size of the steel sheet is less than 10 μm, {111} <112> grains are excessively generated in the primary recrystallization texture, and (110) [001] as the nucleus of secondary recrystallization. ] As a result of the growth of many grains with an orientation deviating from the orientation, the secondary recrystallization orientation of the product is deteriorated and the magnetic properties are deteriorated.
Conversely, when the average grain size of the steel sheet exceeds 35 μm, the frequency of {111} <112> grains is reduced even in the primary recrystallization texture, and (110) [110] [ [001] As a result of suppressing even the grain growth, secondary recrystallization failure occurs, resulting in deterioration of the magnetic properties of the product.
[0095]
Here, the measurement method of the average crystal grain size is a cross section in the plate thickness direction of the steel sheet, and in the region extending from one surface layer to the other surface layer, the number of 1000 or more crystal grains is measured, It is calculated by converting from the area to the equivalent circle diameter.
[0096]
The adjustment of the average crystal grain size in the steel sheet immediately before the final cold rolling as described above can be performed mainly by changing the annealing temperature and time in hot-rolled sheet annealing and intermediate annealing, thereby controlling the average crystal grain size. The superiority of the present invention is that the dispersion control of the inhibitor can be completely independent. In other words, after controlling the dispersion of the inhibitor by the heating rate of hot-rolled sheet annealing, it is possible to appropriately control the average crystal grain size by changing the annealing temperature and time at a temperature of 1125 ° C or lower. It is. In addition to the above-described means, the average crystal grain size can be controlled by changing the annealing atmosphere or the steel components, and it is also effective to use these in combination.
[0097]
Further, in the case of steel containing C in the steel, in the cooling process of the annealing just before the final cold rolling, the precipitation of fine carbide is promoted by the rapid cooling and low temperature holding, and the precipitation size is adjusted, and the primary recrystallization aggregate Tissue control is also a useful means and the invention does not preclude this application. Further, in cold rolling, it is also effective means to control the primary recrystallization texture by warm rolling at a temperature of 150 to 250 ° C. or aging treatment between passes, and the present invention does not hinder this application. .
[0098]
Next, in order to obtain a grain-oriented electrical steel sheet having a high magnetic flux density as expected in the present invention, it is necessary to set the rolling reduction of the final cold rolling to a high pressure of 80 to 95%. By applying the rolling reduction, it is possible to increase the frequency of formation of {111} <112> grains in which secondary recrystallization nuclei easily grow as primary recrystallization textures. In other words, if the rolling reduction is less than 80% or more than 95%, the frequency of {111} <112> grains in the primary recrystallization structure is drastically reduced, and it is difficult to grow the nuclei of secondary recrystallization. Become.
[0099]
The coil after the final cold rolling is then subjected to primary recrystallization annealing. This annealing also serves as decarburization annealing when C is contained in the steel. This annealing is performed at 750 to 900 ° C. for 60 to 180 seconds.
[0100]
The coil after the primary recrystallization annealing is applied to the secondary recrystallization annealing after the annealing separator is applied and then wound into a coil shape. This secondary recrystallization annealing is generally performed as final finishing annealing that also serves as purification annealing. This final finish annealing may be performed by a known method.In particular, in the present invention, Sb is contained in the steel, and it is a treatment for holding at a constant temperature between 800 and 890 ° C. for 15 to 60 hours during the temperature increase, Alternatively, it is effective to accumulate the crystal orientation of the secondary recrystallized grains in the (110) [001] orientation by performing a temperature rise treatment or a temperature fall treatment at a temperature rise rate of 5 ° C./hr or less or a temperature drop rate.
[0101]
After the final finish annealing, the remaining annealing separator is removed, and when it is necessary to increase the insulation resistance, an insulating coating agent is applied and flattened annealing is performed to obtain a product. In addition, the product can be applied with a magnetic domain fragmentation technique such as plasma jet, laser or electron beam irradiation or groove formation, which is consistent with the object of the present invention.
[0102]
【Example】
Example 1
Two slabs of steel ingot symbols C to M having the composition shown in Table 3 were prepared. These slabs are heated to 1400 ° C in an induction furnace, and then hot rolled to a thickness of 2.20 mm by hot rolling using a finishing mill consisting of three rough rolling mills and seven tandem rolling mills. A coil was used.
[0103]
[Table 3]

[0104]
In this hot rolling, by adjusting the amount of coolant water in the rough rolling, one of the slabs of each steel type has a finishing rolling start temperature of 1150 to 1220 ° C and a finishing rolling finish temperature of 890 to 970 ° C. After jet water was jetted onto the steel strip, it was rapidly cooled at a cooling rate of 18 ° C / s, and then wound into a coil at 550 ° C (conforming example).
[0105]
On the other hand, the finish rolling start temperature is set to 1250 to 1310 ° C., the finish rolling end temperature is set to 1120 to 1190 ° C., and then cooling is performed at 8 ° C./s by injecting jet water onto the steel strip. It was carried out at 550 ° C. in the same way as the conforming example (comparative example). The time required from the start of rough rolling to the end of finish rolling was in the range of 230 to 290 seconds.
[0106]
After completion of hot rolling, each steel plate was subjected to hot-rolled sheet annealing at 1000 ° C. for 30 seconds. At this time, the temperature increase temperature was 15 to 17 ° C./s (the temperature increase rate between 600 to 800 ° C. was 13 to 16 ° C. ° C / s). Thereafter, the surface scale was removed by pickling, and then an intermediate plate thickness of 1.40 mm was obtained by cold rolling, followed by intermediate annealing. The conditions for this intermediate annealing are as follows.₂, Balance N₂After heat treatment at 1080 ° C for 60 seconds in a balanced atmosphere, it was rapidly cooled to 350 ° C at a cooling rate of 40 ° C / s using mist water, held at this 350 ° C for 20 seconds, then cooled and acidified. It has been washed. On the other hand, for the intermediate annealing conditions of the steel plate of the comparative example, after heat treatment at 1170 ° C. for 60 seconds in the same atmosphere as the conforming example, it was rapidly cooled to room temperature at a cooling rate of 40 ° C./s using mist water. After that, it is pickled.
[0107]
About these steel plates, after measuring the average crystal grain size of the steel plates after the intermediate annealing, they were subjected to warm rolling and aging between passes at 150 to 220 ° C., and finished to a final plate thickness of 0.19 mm.
These steel plates have a dew point of 60 ° C and 55% H₂And the rest N₂Decarburization and primary recrystallization annealing at 840 ° C for 120 seconds in a balanced atmosphere, followed by 5% TiO₂And 3% SrSO_FourWas applied as an annealing separator, and then wound into a coil shape and subjected to final finish annealing.
[0108]
The conditions for this final finish annealing are as follows. First, for the coils of symbols C, E, H, K, and M containing Sb, N up to 850 ° C. at a temperature increase rate of 30 ° C./hr.₂The temperature rises in, and N₂25% N after holding at 850 ° C for 35 hours in₂And 75% H₂The temperature is raised to 1160 ° C at a rate of 15 ° C / hr in a mixed atmosphere of₂After maintaining at 1160 ° C for 8 hours, the temperature was lowered.
For the coils of symbols D, F, G, I, J, and L, N is heated up to 850 ° C. at a rate of 30 ° C./hr.₂The temperature rises in, and 25% N₂And 75% H₂The temperature is raised to 1160 ° C at a rate of 15 ° C / hr in a mixed atmosphere of₂After maintaining at 1160 ° C for 8 hours, the temperature was lowered.
[0109]
After the final finish annealing, remove the afterimage annealing separator, apply a tension coating agent consisting of 50% colloidal silica and magnesium phosphate, and then apply a flattening treatment that also serves as coating baking at 800 ° C for 1 minute. Further, the product was subjected to magnetic domain fragmentation treatment by irradiating with a plasma jet linearly at intervals of 6 mm in the rolling direction. Table 4 shows the magnetic properties of these products.
[0110]
[Table 4]

[0111]
As is apparent from Table 4, the conforming example satisfying the hot rolling and cold rolling conditions according to the present invention has extremely excellent magnetic properties as compared with the comparative example.
[0112]
(Example 2)
Two slabs of steel ingot symbols C, D, H and I shown in Table 3 were prepared. These slabs were heated to 1350 ° C., and then hot rolled coils having a sheet thickness of 2.40 mm were formed by hot rolling consisting of rough rolling with a roughing mill and finish rolling with a steckel rolling mill.
[0113]
In this hot rolling, the finish rolling start temperature was 980 to 1125 ° C., the finish rolling end temperature was 870 to 1020 ° C., and 490 to 510 seconds were required from the start of rough rolling to the end of finish rolling. After the hot rolling, for each steel type, one coil was jetted with jet water, rapidly cooled to 500 ° C. at a cooling rate of 20 ° C./s, and then wound into a coil shape and allowed to cool (conforming example). On the other hand, the remaining coil was rapidly cooled to 500 ° C. at a cooling rate of 5 ° C./s after completion of hot rolling, and then wound into a coil shape and allowed to cool (Comparative Example).
[0114]
These hot-rolled coils were then subjected to hot-rolled sheet annealing at 1100 ° C for 60 seconds. At this time, the heating control was performed at the time of temperature increase, and the temperature increase rate between 600-800 ° C was 8.5-10.5 ° C. During the cooling, fine carbide was precipitated in the steel at a cooling rate of 20 ° C./s by mist cooling. After this hot-rolled sheet annealing, the average crystal grain size of the steel sheet was measured, and after pickling, it was rolled to a final sheet thickness of 0.34 mm by warm rolling at 150 to 250 ° C. and aging between passes.
[0115]
After final cold rolling, electrolytic degreasing, then dew point 60 ° C, H₂55%, remaining N₂After decarburization and primary recrystallization annealing in a balanced atmosphere, 8% TiO₂Was applied as an annealing separator, and then wound into a coil and subjected to final finishing annealing.
The condition for this final finish annealing is N₂The temperature was raised to 800 ° C at a rate of 30 ° C / hr, and then 20% N₂And 80% H₂After heating up to 1180 ° C at a rate of 15 ° C / hr in the atmosphere of₂After holding at 1180 ° C. for 5 hours in an atmosphere, the temperature was lowered.
After the final finish annealing, the remaining annealing separation agent is removed, and then a tension coating agent composed of 50% colloidal silica and aluminum phosphate is applied, followed by a flattening treatment that also serves as coating baking at 800 ° C. for 1 minute, The product.
Table 5 shows the magnetic properties of these products.
[0116]
[Table 5]

[0117]
As is apparent from Table 5, the steels C and H to which Se is added as an inhibitor component can obtain extremely excellent magnetic properties when the hot rolling and cold rolling conditions according to the present invention are satisfied.
[0118]
(Example 3)
16 slabs of steel ingot symbol C shown in Table 3 were prepared, these slabs were heated to 1420 ° C. in an induction heating furnace, and subjected to rough rolling and finish rolling in the same hot rolling mill arrangement as in Example 1, A hot rolled coil with a thickness of 2.40 mm was used. At this time, by adjusting the amount of roll coolant and strip coolant water in rough rolling, the finish rolling start temperature is set to 1170 to 1210 ° C., the finish rolling end temperature is set to 870 to 930 ° C., and then jet water is jetted to 15 ° C. / After quenching at a cooling rate of s, it was wound into a coil at 550 ° C. At this time, the time required from the start of rough rolling to the end of finish rolling was 350 to 372 seconds.
[0119]
After hot rolling, each steel plate was subjected to hot-rolled sheet annealing at 950 ° C for 60 seconds, but at this time, the heating rate was adjusted and the heating rate between 600 and 800 ° C was 12 to 15 ° C / s. It was. Thereafter, the surface scale was removed by pickling, and after rolling to a sheet thickness of 1.50 mm by cold rolling, intermediate annealing was performed. As conditions for this intermediate annealing, the atmosphere is set at two levels, one is a dry atmosphere condition (dew point 10 ° C or less, 20% N₂And 80% H₂And the other is humid atmosphere conditions (dew point 50 ° C, 50% N)₂And the rest H₂Balance). The soaking temperature was kept constant at 1080 and the soaking times were 5 seconds, 10 seconds, 30 seconds, 60 seconds, 90 seconds, 120 seconds, 180 seconds, and 240 seconds, respectively. After this annealing, it was rapidly cooled to 350 ° C. at a cooling rate of 40 ° C./s with mist water, held at this 350 ° C. for 25 seconds, then cooled and pickled. Subsequently, after measuring the average crystal grain size of these steel plates, the steel sheet was warm-rolled at 100 to 230 ° C. and finished to a final thickness of 0.22 mm.
[0120]
Next, in order to provide a groove for magnetic domain refinement treatment by degreasing, acid-resistant masking treatment is selectively applied to the steel sheet, and the non-treated portion is subjected to electrolytic etching, with a width of 150 μm and a depth of 20 μm. Grooves extending in the direction of 85 ° to 4 mm in the rolling direction were provided.
[0121]
Next, these steel sheets were dew point 50 ° C, 55% H₂And the rest N₂After decarburization and primary recrystallization annealing at 850 ° C for 120 seconds in a balanced atmosphere, 8% TiO₂And 3% Sr (OH)₂・ 8H₂After applying MgO containing O as an annealing separator, it was wound into a coil and subjected to final finish annealing.
The condition for this final finish annealing is N₂15% N after 45 hours at 840 ℃₂And 85% H₂In a mixed atmosphere with a temperature increase rate of 20 ° C / hr to 1160 ° C,₂The temperature was lowered after holding at 1160 ° C for 5 hours.
[0122]
After the final finish annealing, after removing the remaining annealing separator, a tension coating consisting of 50% colloidal silica and magnesium phosphate is applied, followed by a flattening treatment that also serves as a coating baking at 800 ° C for 1 minute. And product.
FIG. 3 shows the relationship between the magnetic properties of these products and the average crystal grain size of the steel sheet after intermediate annealing. As shown in FIG. 3, according to the present invention, a product having excellent magnetic properties is obtained in the range where the average crystal grain size of the steel sheet is 10 to 35 μm.
[0123]
Example 4
Three slabs of steel ingot symbols A and B shown in Table 3 are each heated to 1200 ° C. in a gas furnace, subjected to rough rolling and finish rolling by the same hot rolling mill arrangement as in Example 1, and both A and B Two were hot-rolled to a plate thickness of 2.70 mm and the other one was hot-rolled to a plate thickness of 2.00 mm to form hot rolled coils. During this hot rolling, the finish rolling start temperature was set to 1030 to 1090 ° C., and the finish rolling end temperature was set to 830 to 890 ° C. After the finish rolling was completed, jet water was sprayed to quench at a cooling rate of 14 ° C./s and wound into a coil at 550 ° C. The required time from the start of rough rolling to the end of finish rolling at this time was 284 to 320 seconds.
[0124]
After hot rolling, hot-rolled sheet annealing was performed at a soaking temperature of 1000 ° C. At this time, one of the hot-rolled sheets with a thickness of 2.70 mm had a heating rate of 600-800 ° C at 3 ° C / s. On the other hand, the heating rate between 600 and 800 ° C. was set to 14 ° C./s by rapid heat treatment. Further, a hot rolled sheet having a thickness of 2.00 mm was set to a temperature rising rate of 600 to 800 ° C. at 16 ° C./s. The soaking time was set to 50 seconds so that the average crystal grain size was 18 to 21 μm. These steel sheets were finished to a final sheet thickness of 0.49 mm by warm rolling at 250 ° C. after measuring the average crystal grain size.
[0125]
After this, degreasing treatment was performed. For steel A, the dew point was 60 ° C and 50% H.₂Remaining N₂Decarburization and primary recrystallization annealing at 840 ° C for 200 seconds in a balanced atmosphere. Steel B has a dew point of 40 ° C and 40% H₂, Balance N₂A primary recrystallization annealing was performed at 840 ° C. for 60 seconds in a balanced atmosphere. After this 5% TiO₂An MgO annealing separator containing bismuth was applied, wound into a coil, and subjected to final finish annealing.
[0126]
The condition for this final finish annealing is N₂The temperature was raised to 900 ° C at a rate of 30 ° C / hr, then 25% N₂And 75% H₂In a mixed atmosphere, the temperature was raised to 1180 ° C at a rate of 15 ° C / hr, followed by H₂The temperature was lowered after holding at 1180 ° C for 5 hours.
[0127]
After the final finish, the remaining annealing separator is removed, then a tension coating consisting of 50% colloidal silica and magnesium phosphate is applied, followed by a flattening treatment that also serves as a coating baking at 800 ° C for 1 minute. It was. Table 6 shows the magnetic properties of these products.
[0128]
[Table 6]

[0129]
As shown in Table 6, products that satisfy the conditions of the hot rolling process and the cold rolling process according to the present invention exhibit excellent magnetic properties.
[0130]
(Example 5)
Eight slabs of steel ingot symbol K shown in Table 3 were prepared. These slabs are heated to 1400 ° C and subjected to three rounds of rolling and finishing rolling by a hot rolling facility consisting of one roughing mill and six stand finishing mills, and a 2.20mm hot rolled coil It was. At this time, the amount of coolant water in the rough rolling is adjusted so that the finish rolling start temperature is 1100 to 1150 ° C., the finish rolling end temperature is 920 to 970 ° C., and after finish rolling is finished, jet water is injected to reach 16 ° C./s. The sample was rapidly cooled at a cooling rate and wound into a coil at 500 ° C. The time required from the start of rough rolling to the end of finish rolling at this time was 198 to 216 seconds.
[0131]
After hot rolling, hot-rolled sheet annealing was performed at a heating rate of 10 ° C / s (12 ° C / s between 600-800 ° C) and a soaking temperature of 1000 ° C. After pickling and cold rolling, 1.50mm Intermediate plate thickness. Subsequent intermediate annealing has a dew point of 45 ° C and 60% H₂, Balance N₂Heat treatment for 60 seconds in a balanced atmosphere, followed by rapid cooling with mist water at a cooling rate of 40 ° C / s. The soaking times for this intermediate annealing were 1000 ° C and 1050 ° C, respectively. , 1075 ° C, 1100 ° C, 1125 ° C, 1150 ° C, 1175 ° C, 1200 ° C.
[0132]
The steel sheet after the intermediate annealing was subjected to pickling after measuring the average crystal grain size, and then finished to a final sheet thickness of 0.22 mm by cold rolling consisting of warm rolling at 150 to 230 ° C. and aging between passes. .
[0133]
After this, a degreasing treatment is performed, and the dew point is 60 ° C and 50% H.₂, Balance N₂Decarburization and primary recrystallization annealing at 840 ° C for 120 seconds in a balanced atmosphere, followed by 8% TiO₂After applying an MgO annealing separator containing, a coil was wound up and subjected to final finishing annealing. This final finish annealing condition is N up to 860 ° C.₂The temperature was raised at a rate of 40 ° C / hr in the inside, and then N for 25 hours at 860 ° C.₂25% N after holding in₂And 75% H₂After raising the temperature to 1200 at a rate of 12 ° C / h in the atmosphere of₂The temperature was lowered after holding at 1200 ° C. for 5 hours.
[0134]
After the final illuminance, the remaining annealing separator is removed, and as a magnetic domain subdivision process, grooves with a width of 100 μm, depth of 15 μm, and extending from the rolling direction to 85 ° are formed at intervals of 4 mm in the rolling direction. Then, after applying a tension coating composed of 50% colloidal silica and magnesium phosphate, a flattening treatment was performed which also served as coating baking at 800 ° C. for 1 minute to obtain a product.
Table 7 shows the magnetic properties of these products.
[0135]
[Table 7]

[0136]
As shown in Table 7, the average grain size after the intermediate annealing is as small as 8.2 μm, soaking temperature: products of 1000 ° C and soaking temperatures of 1150 ° C, 1175 ° C, 1200 ° C and soaking of the present invention. The product having a condition higher than the temperature has poor magnetic properties, but the product satisfying the cold rolling process according to the present invention has very good magnetic properties.
[0137]
【The invention's effect】
Thus, according to the present invention, when a grain-oriented electrical steel sheet containing Al is produced, the control of various conditions in the hot rolling process and the new precipitation control method for the inhibitor AlN by controlling the cold rolling conditions are extremely excellent. A grain-oriented electrical steel sheet having magnetic properties can be obtained.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a diagram showing the particle size distribution and the generation frequency of a hot rolled sheet according to the present invention, a steel sheet immediately after heating at 1000 ° C. and a precipitate after decarburization and primary recrystallization annealing.
FIG. 2 is a diagram showing the particle size distribution and the generation frequency of a conventional hot-rolled sheet, a steel sheet immediately after heating at 1000 ° C. and a precipitate after decarburization and primary recrystallization annealing in hot-rolled sheet annealing.
FIG. 3 is a diagram showing the relationship between the average crystal grain size and magnetic properties of a steel sheet after intermediate annealing in an example.

Claims (8)

Containing 0.10 wt% or less of C, 2.5 to 5.0 wt% of Si, 0.005 to 0.10 wt% of Mn , 0.005 to 0.040 wt % of Al and 0.0040 to 0.0130 wt % of N, with the balance being Fe and inevitable impurities The directionality electrical steel slab to be subjected to hot rolling in which the time from the start of rough rolling to the end of finish rolling is less than 450 seconds, followed by hot-rolled sheet annealing, and then once or twice with intermediate annealing In the manufacturing method of the grain-oriented electrical steel sheet that is subjected to the primary recrystallization annealing and the secondary recrystallization annealing after the final sheet thickness by cold rolling of
In the above hot rolling, the finish rolling start temperature is set to 1000 to 1230 ° C, the end temperature is set to 800 to 1100 ° C, and the cooling rate from the finish rolling to 700 ° C is set to 10 ° C / s or more and wound at 650 ° C or less. to take,
The temperature increase rate between 600-800 ° C in the temperature increase process of the hot-rolled sheet annealing is 5-30 ° C / s, and the temperature of this hot-rolled sheet annealing and the annealing before the final cold rolling is 1125 ° C or less. To do,
Of oriented electrical steel sheets towards coupling characterized in that the and reduction ratio of final cold rolling rolling for adjusting the average crystal grain size of the steel strip of the final cold rolling immediately before the 10~35μm with 80% to 95% Production method. Method for producing oriented electrical steel sheets towards claim 1, wherein the adjusting the average crystal grain size of the final cold rolling immediately before the steel sheet 12.5～27.5Myuemu. Steel slabs, which further comprises containing 0.005 to 0.030 wt% in total of one or two of S and Se,
1000 to 1200 ° C. The starting temperature of finish rolling in the hot rolling method of oriented electrical steel sheet towards the claim 1, wherein a to 850 to 1000 ° C. The end temperature. Containing 0.10 wt% or less of C, 2.5 to 5.0 wt% of Si, 0.005 to 0.10 wt% of Mn , 0.005 to 0.040 wt % of Al and 0.0040 to 0.0130 wt % of N, with the balance being Fe and inevitable impurities The directionality electrical steel slab to be subjected to hot rolling for 450 seconds or more from the start of rough rolling to the end of finish rolling, followed by hot-rolled sheet annealing, and then one time or two times with intermediate annealing In the manufacturing method of the grain-oriented electrical steel sheet that is subjected to the primary recrystallization annealing and the secondary recrystallization annealing after the final sheet thickness by cold rolling of
The steel slab, which further comprises 0.005～0.030Wt% including a Se,
After limiting the time from the start to the end of finish rolling in the hot rolling to 460 seconds or less, the finish rolling end temperature is set to 850 to 1150 ° C, and the cooling rate from the finish rolling to 700 ° C is set to 10 ° C. Winding at 650 ° C or less as ℃ / s or more,
The temperature increase rate between 600-800 ° C in the temperature increase process of the hot-rolled sheet annealing is 5-30 ° C / s, and the temperature of this hot-rolled sheet annealing and the annealing before the final cold rolling is 1125 ° C or less. To do,
Of oriented electrical steel sheets towards coupling characterized in that the and reduction ratio of final cold rolling rolling for adjusting the average crystal grain size of the steel strip of the final cold rolling immediately before the 10~35μm with 80% to 95% Production method. The steel slab further contains 0.005 to 0.060 wt% of Sb, the cooling rate in the hot-rolled sheet annealing step is 5 to 60 ° C / s, and the temperature is raised to 800 to 890 ° C in the secondary recrystallization annealing. The temperature is maintained at a constant temperature for 15 to 60 hours, or the temperature is increased or decreased at a temperature increase rate or a temperature decrease rate of 5 ° C./hr or less in the temperature range. method for producing oriented electrical steel sheets towards according to any one selected from. Steel slabs Cu The 0.005 ~ 0.30wt The method for producing a grain-oriented electrical steel sheet according to any one of Claims 1 to 5, wherein the grain-oriented electrical steel sheet is contained. The steel slab is one or two selected from Sn, P, Bi, As, B, Ge, V, Nb, Cr and Te, Sn and Cr are 0.03 to 0.30 wt%, and Bi is 0.005. ~0.020 wt%, P, Ge, V, Nb, as, Te , respectively 0.005 to 0.030 wt%, any B is selected from claims 1 to 6, characterized in that it contains in the range of 0.0005～0.0020Wt% method for producing oriented electrical steel sheets towards according to any one of claims. Steel slab further method for producing oriented electrical steel sheets towards according to 1, wherein one selected from claims 1 to 7, characterized in that it contains 0.005～0.020Wt% of Mo.

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