JP3885391B2 - Method for producing grain-oriented electrical steel sheet - Google Patents

Description

【００１９】
【表２】

【００２０】
まず、柱状晶比率が30％の場合、一部で二次再結晶が起こっているが、いずれもB₈は1.9 Ｔ未満である。次に、柱状晶比率が60％となったときにおいても加熱温度が1300℃の場合は二次再結晶は完全ではなく、磁束密度B₈は低くなっている。柱状晶比率が60％で加熱温度が1400℃の場合は、1300℃での加熱の場合に比較して、いずれもB₈は上昇している。しかしながら、Alを含まない場合は二次再結晶は起こっているが、一部が二次再結晶が不完全となっているためB₈は1.9 Ｔに達せず低い値となっている。ところが、Alが0.001 〜0.008 wt％の範囲にある場合には二次再結晶も完全となってB₈は1.9 Ｔ以上が得られることがわかった。
【００２１】
更に、これらの脱炭焼鈍板を用いて、900 ℃でそれぞれ24ｈの等温焼鈍をAr雰囲気中で行った。
上記試験の結果得られた試料のそれぞれについて、
(1) 脱炭焼鈍後の一次再結晶粒径（円近似による。以下同様。）、
(2) 900 ℃で24ｈの等温焼鈍後の一次再結晶粒径（これは二次再結晶開始直前の一次再結晶粒に相当する。）
を測定・調査した。その結果を図１に示す。
【００２２】
まず、柱状晶率を60％とした試料について、熱延前に1300℃に加熱した場合の脱炭一次再結晶後の一次再結晶粒径（折線ｃ）は、基本成分に対してAlの含有量が増加しても結晶粒径に大きな変化は認められなかった。これら脱炭焼鈍板を900 ℃で24ｈ保持した後の粒径、すなわち二次再結晶開始直前の一次再結晶粒径（折線ｄ）は、いずれのAl含有量においても同様に粒径が粗大化した。
【００２３】
これに対し、熱延前の加熱を1400℃とした場合は、脱炭一次再結晶後の一次再結晶粒径（折線ａ）はAlの含有量が増すとともに小さくなり、Alが0.006 wt％を超えるあたりから、再び大きくなった。また、Alを含有していない場合は900 ℃で24ｈ保持した後の粒径が粗大化しているが、Al含有量が0.001 wt％から0.008 wt％の範囲では粒径の粗大化が抑えられていることがわかった。
【００２４】
次に、柱状晶率が30％のものについては1400℃で加熱した試料のみ図１に示した。これらの試料は、加熱温度を1400℃と高くしたにもかかわらず24ｈの焼鈍後にかなり一次再結晶粒径が粗大化してしまっている。
【００２５】
上記のような結果を生じる原因について発明者らは鋭意研究した結果、二次再結晶直前の一次再結晶粒径の粗大化が抑えられた柱状晶率が60％でかつ、Al含有率が0.001 〜0.008 wt％の場合においては、熱延前の加熱時の固溶が良好になっていることが明らかになった。これについて以下に詳細を記す。
【００２６】
上述した実験材ａの各組成を有する各スラブを1300℃及び1400℃にそれぞれ加熱した後、水焼き入れを行った。この加熱前後のスラブについて光学顕微鏡及び電子顕微鏡で詳細に調査した結果、多数の析出物が確認された。これら析出物の構成成分を分析したところインヒビター成分であるＢ及びＮが検出された。
表１，２に、熱延前のスラブ加熱条件及び素材へのAl添加量を変えた場合の加熱後析出物の有無を観察した結果を併せて示す。
【００２７】
この結果より、加熱温度が1300℃のとき及び柱状晶率30％で加熱温度が1400℃のときは、いずれのAl含有量においても残存析出物が確認されている。また、柱状晶率を60％とし加熱温度を1400℃としたときには、Alを含有していない場合では残存析出物が確認されたが、Alが0.001 〜0.008 wt％含有されているときには、残存析出物は観察されなかった。
【００２８】
次に、上記ａの組成のスラブのうち、Alを含有していない素材及びAlを0.006 wt％含有した素材について、加熱前に観察された析出物それぞれを画像解析装置により粒径を計測し、析出物粒径の分布と析出物の平均粒径を求めた。これを図２に示す。まず、柱状晶率60％の素材について、Alを含有しない鋼（図２ａ）は、析出物粒径の分布が広く、かつ10μm を超える粗大な析出物が多く、その平均粒径も7.74μm と大きくなっている。これに対し、Alを含有した鋼（図２ｂ）は、10μm を超える粗大な析出物が少なく、平均粒径も5.65μm となっており、析出物が比較的細かくなっていることが明らかになった。
【００２９】
次に、柱状晶率が30％の素材では、Alを0.006 ％含有した場合（図２ｃ）であっても10μm を超える粗大な析出物が多く、その平均粒径も7.16μm と大きくなっている。このスラブ内の析出粒子に関して、柱状晶部では10μm 以下の粒子が多数を占めるが、等軸晶部では10μm 以上の粒子が多くなり、これにより平均粒径値が引き上げられていることがわかった。
【００３０】
よって表１のNo. 20〜23の試料では柱状晶率を高くする、すなわち冷却を強化して急冷し、更にAlを0.001 〜0.008 wt％の範囲で含有させることによって初めてインヒビター成分が細かく析出し、更に加熱温度を1400℃の高温としたことにより、析出物の固溶が促進され、結果として残存析出物が観察されなかったものと考えられる。
【００３１】
このように比較的細かく析出したインヒビター成分が一旦完全に固溶し、後の工程で更に微細に再析出することにより、二次再結晶直前の一次再結晶粒の粗大化が抑えられ、強い粒成長抑制の効果が発現されたものと考えられる。
【００３２】
（実験２）
実験１において、Ｂ及びＮを含有した鋼にAlを含有させることにより、二次再結晶の安定化及び良好な磁気特性が得られた。そこで、Ｂを添加せずに実験１と同様な範囲のAlを含有させた場合の磁気特性を調査した。
【００３３】
実験材の組成は下記のとおりである。
実験材ｂ． Ｃ：0.070 wt％、Si：3.23wt％、Mn：0.07wt％、Ｎ：0.0080wt％、Se：0.020 wt％、Sb：0.025 wt％を含有し、残余は不可避的不純物と鉄とからなる基本成分、及びこの基本成分にAl：0.0010wt％、0.0030wt％、0.0060wt％、0.0080wt％、0.0100wt％とそれぞれ変化させて含有させた鋼を用いた。
【００３４】
上記各組成を有する連続鋳造スラブを製造する際、柱状晶率を60％とし、これを1400℃に加熱後、熱間圧延により板厚2.6 mmの熱延板とし、950 ℃で2 min の熱延板焼鈍を行ってから、1.8 mm厚に冷間圧延し、1050℃で1 min の中間焼鈍後、最終冷間圧延を行って0.34mmの冷延板とした。この冷延板について、840 ℃で3 min の脱炭焼鈍を施し、Ｃ：0.002 ％以下に脱炭した。このそれぞれの試料にMgO を主成分とする焼鈍分離剤を塗布して、850 ℃から1200℃まで15℃/hの昇温速度で加熱して仕上焼鈍を行った。得られた電磁鋼板の磁気特性及び被膜外観の状況を表３に示す。
【００３５】
【表３】

【００３６】
以上の結果より、Alの添加のみでは二次再結晶が起こらず、磁気特性も劣化することが確認された。また、Al含有量が多くなると被膜外観が白っぽく変化し劣化することがわかった。
【００３７】
（実験３）
Ｃ：0.068 wt％、Si：3.24wt％、Mn：0.07wt％、Ｂ：0.0040wt％、Ｎ：0.0075wt％、Se：0.019 wt％、Sb：0.025 wt％、Al：0.0060wt％を含有し、残余は不可避的不純物と鉄とからなる鋼について、連続鋳造により製造した柱状晶率45％となるスラブを用意した。これを1300〜1425℃の範囲において80min までの様々な加熱時間によるスラブ加熱後、熱間圧延により板厚2.2 mmの熱延板とし、900 ℃で2 min の熱延板焼鈍を行ったのち、1.5 mm厚に冷間圧延し、1000℃で1 min の中間焼鈍後、最終冷間圧延を行って0.22mmの冷延板とした。これらの冷延板について、830 ℃で2 min の脱炭焼鈍を施し、Ｃ：0.002 ％以下に脱炭した。このそれぞれの試料にMgO を主成分とする焼鈍分離剤を塗布して、850 ℃から1200℃まで20℃/hの昇温速度で加熱して仕上焼鈍を行った。得られた電磁鋼板の磁気特性の良否を図３に示す。図３において○印は磁束密度B₈が1.9 Ｔ以上のものを表し、×印は磁束密度が1.9 Ｔ未満となったものを表している。
【００３８】
この図より、スラブ加熱時間ｔ（min ）が加熱温度Ｔ（℃）で決定される次式、
１／５×（1450−Ｔ）≦ｔ≦２／５×（1500−Ｔ）
を満足する範囲内で高磁束密度の材料が得られることが明らかとなった。
【００３９】
上記にこの発明に係わる重要ポイントについて発明したが、以下、この発明の実施形態を具体的に説明する。
（化学成分）
Ｃ：0.03〜0.10wt％
Ｃ量が0.10wt％を超えると、γ変態量が過剰となり、熱間圧延中のＢの分布が不均一となりＢＮの分布の均一性を阻害する結果となり有害である。また、脱炭焼鈍の負荷も増大し脱炭不良を発生し易くなる。一方、0.03wt％未満では二次再結晶が不完全となり、同じく磁気特性が劣化する。したがって、Ｃは0.03〜0.10wt％の範囲に限定される。
【００４０】
Si：2.5 〜4.5 wt％
Si は電気抵抗を増加させ鉄損を低減するために必須の成分であり、このため2.5 wt％以上含有させることが必要であるが、4.5 wt％を超えると加工性が劣化して、圧延や製品の加工が極めて困難になるので2.5 〜4.5 wt％の範囲とする。
【００４１】
Mn：0.05〜1.5 wt％
Mnも電気抵抗を高め、また、製造時の熱間加工性を向上させるので必要な成分である。この目的のためには0.05wt％以上の含有が必要であるが、1.5 wt％を超えて含有させた場合にはγ変態を誘起して磁気特性が劣化するので0.05〜1.5 wt％の範囲とする。
【００４２】
Ｂ及びＮ：
この発明においては、主たるインヒビター成分としてサブスケールの安定生成と、それによる良好な下地被膜の生成のためＢＮを用いる。特に、最終冷間圧延圧下率が80％以上の場合、二次再結晶温度が非常に高くなるため、鋼中には高温で安定なインヒビター成分としてＢ及びＮを含有させることが必須である。このうちＢは0.0010〜0.0060wt％の範囲で含有させる。Ｂの含有量が0.0010wt％未満の場合、析出するＢＮの量が不足し良好な二次再結晶を得ることができず、0.0060wt％を超える場合、固溶温度が増加し、通常の加熱では熱延前にＢＮを完全に固溶させることが不可能となるためである。Ｎの含有量は0.0030wt％以上が必要であり、Ｎ量が0.0030wt％未満では析出するＢＮの量が不足する。また、Ｎ量が0.010 wt％を超えると鋼中でガス化し、フクレなどの欠陥が生ずるので0.0030〜0.010 wt％の範囲とする。
【００４３】
補助インヒビター成分：
Ｂ及びＮを補助するインヒビター成分として、Se、Ｓを単独もしくは複合して含有させることが必要である。これらの成分は鋼中にMn化合物あるいはCu化合物として析出するので、抑制効果を維持するには合計で0.010 wt％以上が必要であるが、0.040 wt％を超えるとスラブ加熱温度を極めて高温にしても完全に固溶させることができず、粗大な析出物のまま残留するのでかえって有害である。したがって、0.010 〜0.040 wt％の範囲とする。なお、Mn量との関係で、Mn (wt%)／（Ｓ (wt%)＋Se (wt%)）の値が2.5 より小さいと熱間圧延中に粒界割れや耳割れが著しく増加するためMn／（Ｓ＋Se）≧2.5 とすることが実用上必要である。
【００４４】
その他のインヒビター元素：
Cu、Sb、Sn、Bi及びMoは、インヒビターとして抑制力を強化する補助的役割を有するので、必要に応じて添加することができる。これらの添加量の好適範囲は0.005 〜0.30wt％である。その他、NiやCoの添加も鋼板の表面性状を改善するので、適宜添加すればよい。
【００４５】
Al：0.0010〜0.0080wt％
この発明ににおいては、微量のAlの添加により二次再結晶が安定化し、良好な磁気特性が得られている。AlはAlN を形成するためインヒビター元素として知られているが、前述の実験結果において二次再結晶の安定性及び磁気特性の改善に対する効果が認められたことから推定するところ、この発明のように微量な範囲のAlを添加することによりＢＮもしくはMn（Se＋Ｓ）の析出挙動が変化したことが考えられる。ひとつは連続鋳造時にAlの存在により析出温度が低下し均一微細に析出したこと、もうひとつは加熱時に複合した析出粒子となることによりオストワルド成長が抑えられ粗大化が抑制されたことが推定される。
【００４６】
このAlの添加によりスラブ加熱前において析出物が微細化することにより固溶が容易となり、熱延以後にさらに微細にインヒビターが再析出した結果、一次再結晶粒の粒成長抑制力が高くなり、最終的に良好な磁気特性が得られたものと考えられる。
このAlの添加量が0.0010wt％未満の場合には上記の効果が得られず、0.0080wt％を超えると二次再結晶粒径が粗大化して、鉄損が劣化する。以上の理由からAlの添加量は0.0010〜0.0080wt％の範囲とする必要がある。
【００４７】
また、Alには添加量が多くなると脱炭焼鈍でのサブスケールの生成や、仕上焼鈍でのフォルステライトの生成を困難にするという側面がある。このような被膜の劣化により、被膜外観のみならず磁気特性も劣化する。これらの劣化を防ぐためにもAlは0.0080wt％以下に制限する必要がある。
このような適正範囲が存在する理由は明らかではないが、固溶Al量が多くなると鋼板表層付近で酸化物を形成し易くなり、脱炭焼鈍でのサブスケール生成や仕上焼鈍でのフォルステライト被膜の生成を阻害する等の悪影響が現れるものと考えられる。
【００４８】
（圧延条件）
以上の成分に調整された鋼は、連続鋳造されスラブとなる。このときスラブ内の組織における柱状晶の比率を多くすることが必要である。柱状晶内の析出粒子は、等軸晶部に比べ細かく、この比率を多くすることにより続くスラブ加熱での固溶を良好なものとさせる。そのため柱状晶の比率は40％以上が必要となる。
【００４９】
続くスラブ加熱では加熱温度を1350℃以上とすることが必要である。この発明ではAlを上記に示した所定の量添加したうえで、連続鋳造でのスラブ内の柱状晶率を40％以上とし、更に、スラブ加熱温度を1350℃以上とすることにおいてはじめて、ＢＮ、Mn（Se＋Ｓ）を一旦完全に固溶させることが可能となり、その後の再析出により均一微細なインヒビターの分散析出状態を得ることができる。
【００５０】
また、スラブ加熱では、析出したＢＮの粗大化が問題となる。これはＢの拡散係数が大きいことに由来するものと思われる。よって、1250℃から目標となる加熱温度までの昇温に要する時間を１時間以内とし、更に、前述の実験より均熱時間ｔ（min ）を均熱温度Ｔ（℃）で決定される次式、
１／５×（1450−Ｔ）≦ｔ≦２／５（1500−Ｔ）
（Ｔ：スラブ加熱温度）
の範囲とすることが必要である。
【００５１】
なお、引き続く熱間圧延に際し、スラブ加熱前後において組織均一化のための厚み低減処理や幅圧下処理など、公知の技術を随時加えることも可能である。熱間圧延によって得られた熱延板は、必要に応じた熱延板焼鈍後、１回の冷間圧延により最終板厚とする冷延１回法、又は必要に応じて熱延板焼鈍を施した後、第１回目の冷間圧延、更に中間焼鈍を挟んで第２回目の冷間圧延を施す冷延２回法が採用できる。また、複数の中間焼鈍を挟んで３回以上の冷間圧延を施すこともできる。
【００５２】
冷間圧延の圧下率については、従来公知のように冷延２回法の場合、第１回目の圧延は15〜60％の圧下率とする。この圧下率が15％未満の場合は圧延再結晶の機構が作用しないため結晶組織の均一化が得られず、60％を超えると結晶組織の集積化が起こり第２回目の圧延の効果が得られなくなるためである。また、最終圧延の圧下率は80〜90％とする。圧下率が90％を超えた場合、二次再結晶が困難となり、80％未満では良好な二次再結晶粒の方位が得られず、製品の磁束密度が劣化するからである。
【００５３】
最終冷間圧延に際して、100 〜350 ℃での温間圧延もしくは100 〜350 ℃で10〜60min のパス間時効処理は、一次再結晶の集合組織を一層改善することが可能となるので、この発明において採用することは好ましい。また、最終冷間圧延後に、公知の磁区細分化処理を施すことも可能であり、例えば鋼板表面に線状の溝を設ける処理などを行うことができる。
【００５４】
以上の工程により最終板厚とした鋼板は、公知の手法による脱炭・一次再結晶焼鈍を施し、MgO を主成分とする焼鈍分離剤を鋼板表面に塗布し最終仕上焼鈍に供される。そのときTi化合物を添加すること、あるいはCaやＢを焼鈍分離剤中に含有させることは磁気特性を更に向上させる効果がある。
【００５５】
最終仕上焼鈍においては、昇温途中の少なくとも900 ℃以上からはH₂を含有する雰囲気中で昇温することが必要である。すなわち、高温までN₂のみの雰囲気中で焼鈍を行うと、最終仕上焼鈍中に窒化が生じ方位の劣る結晶粒が二次再結晶し磁束密度の劣化を招いてしまうからであり、よって最終仕上焼鈍中の雰囲気は少なくとも900 ℃以上においてH₂を通入することが必要である。また、H₂雰囲気は上記被膜中の酸化物や窒化物の形成に重要な働きをしており、900 ℃以上の焼鈍の中期から後期において特に還元性を強めておくことが必要であると考えられる。
【００５６】
最終仕上焼鈍ののちは、未反応の焼鈍分離剤を除去した後、鋼板表面に絶縁コーティングを塗布して製品となすが、必要に応じてコーティング塗布前に鋼板表面を鏡面化してもよく、また、コーティングの塗布焼き付け処理を平坦化処理と兼ねることも可能である。更に、二次再結晶後の鋼板に対し、公知の磁区細分化処理、、すなわちプラズマジェットやレーザー照射を線状領域に施したり、突起ロールによる線状の凹み領域を設けたりする処理を行い、鉄損低減効果を得ることもできる。
【００５７】
【実施例】
表４に示す成分及び残余は鉄及び不可避的不純物よりなる連続鋳造スラブを用意した。
【００５８】
【表４】

【００５９】
これらの連続鋳造スラブについて冷却速度の制御により柱状晶率を25％及び70％とした各二本のスラブを1250℃から1420℃まで50min で加熱し15min 均熱した後、板厚2.2 mmまで熱延し、550 ℃でコイル状に巻き取り熱延板とした。この熱延板に対し1000℃、60s の熱延板焼鈍を施し、20℃/sで急冷後、１回目の冷延で板厚1.6mm に仕上げた。この鋼板に1050℃まで昇温して60s 保持する中間焼鈍を施し、40℃/sで急冷し、冷間圧延の途中に300 ℃，30min 、パス間時効処理を行い、それぞれ0.22mm厚に仕上げた。得られた冷延板には脱脂処理、840 ℃で2 min の脱炭焼鈍を施した後、MgO にSrSO₄ を2 ％、TiO₂を8 ％添加した焼鈍分離剤を塗布してから最終仕上焼鈍を施した。この最終仕上焼鈍の条件は、850 ℃までN₂中で30℃/hで昇温した後、850 ℃から1200℃までを50％N₂・50％H₂中で20℃/hで昇温し1200℃ではH₂中で8 h 保持し、その後、600 ℃まではH₂中で、600 ℃からはN₂の雰囲気で降温するものとした。最終仕上焼鈍後、未反応の焼鈍分離剤を除去し、60％のコロイダルシリカを含有するリン酸マグネシウムを張力コーティングとして塗布、840 ℃で焼き付けて製品とした。得られた製品の磁気特性は表５のとおりである。
【００６０】
【表５】

【００６１】
表５から明らかなように、ＢＮをインヒビターとして用いる方向性電磁鋼板を製造するに際し、素材スラブ中にAlを微量含有させ、かつ、スラブ中の柱状晶率を高めた場合には、極めて高い磁束密度と、低い鉄損特性が得られている。
【００６２】
（実施例２）
表６に示す成分と、残余は鉄及び不可避的不純物よりなる連続鋳造スラブを用意した。
【００６３】
【表６】

【００６４】
これらの連続鋳造スラブについて、冷却速度の制御により柱状晶率を83％とし、1250℃から1400℃までを40min で加熱し、35min 均熱した後、2.6 mm厚まで熱延し、550 ℃でコイル状に巻き取り熱延板とした。
この熱延板に対し、900 ℃で60s 均熱する熱延板焼鈍を施した後、20℃/sで急冷後、酸洗し、１回目の冷延で1.8 mmに仕上げた。
【００６５】
次いで、1050℃まで昇温し、60s 保持する中間焼鈍を施し、25℃/sで急冷した。上記により得られた各２枚の鋼板のうち、１枚は250 ℃の温間圧延を施し、更に、0.5 ％のCaと0.09％のＢを含有するMgO にSrSO₄ を4 ％、TiO₂を7 ％添加してなる焼鈍分離剤を塗布し、最終仕上焼鈍を行った。最終仕上焼鈍の条件は、850 ℃まではN₂中で30℃/hで昇温し、850 ℃から1050℃までは25％N₂と75％H₂との混合雰囲気中で15℃/hで昇温し、さらに、H₂中で25℃/hで1200℃まで昇温し、この1200℃で8 h 保持した後、600 ℃までH₂中で降温後、600 ℃からはN₂の雰囲気で降温するものとした。かかる仕上焼鈍後、未反応の焼鈍分離剤を除去し、50％のコロイダルシリカを含有するリン酸マグネシウムを張力コーティングとして塗布し、840 ℃で焼き付けて製品とした。これらの製品の磁気特性は表７のとおりである。
【００６６】
【表７】

【００６７】
表７から明らかなように、ＢＮをインヒビターとして用いる方向性電磁鋼板を製造するに際し、素材スラブ中にAlを微量含有させた発明例は、極めて高い磁束密度と、低い鉄損特性が得られ、しかも被膜外観も良好である。更に、冷間圧延の際に温間圧延を施した場合には、磁気特性が一層向上している。
【００６８】
【発明の効果】
かくしてこの発明によれば、ＢＮを主たるインヒビターとして利用しながら磁束密度が高く、鉄損が低い方向性電磁鋼板の製造が可能となり、その結果、良好な被膜特性と、高い磁束密度の両立が可能となり、従来に比べ、更に一層の鉄損値の低下が可能になった。
【図面の簡単な説明】
【図１】この発明に至る基礎的実験におけるAl含有量と一次再結晶粒径との関係を示すグラフである。
【図２】この発明に至る基礎的実験におけるAl含有の有無による析出物分布の違いを表すグラフである。
【図３】この発明に至る基礎的実験におけるスラブ加熱温度及び加熱時間に対する磁気特性の良否を表すグラフである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a grain-oriented electrical steel sheet used for an iron core of a transformer or a generator, and more particularly to a method for producing a grain-oriented electrical steel sheet having particularly high magnetic flux density and extremely low iron loss.
[0002]
[Prior art]
A grain-oriented electrical steel sheet containing Si and having a crystal orientation of {110} <001> orientation or {100} <001> has excellent soft magnetic properties, and therefore is used as various core materials in commercial frequency ranges. Widely used. The characteristic required for such an electrical steel sheet is the loss when magnetized to 1.7 T at a frequency of 50 Hz. _17/50 It is important that the iron loss expressed in (W / kg) is low.
[0003]
In general, it is effective to reduce eddy current loss in order to reduce the iron loss of electrical steel sheets. For this reason, the method of increasing the electrical resistance by increasing the Si content, the method of reducing the steel sheet thickness, the crystal of the product A method for reducing the grain size and a method for improving the magnetic flux density by increasing the degree of crystal integration are known. Among these, the method of increasing the Si content has limitations because it causes deterioration of the rollability and workability when Si is excessively contained, and the method of reducing the steel plate thickness, the method of reducing the crystal grain size However, this is not preferable because it causes an extreme increase in manufacturing cost.
[0004]
Regarding the method of improving the magnetic flux density by increasing the degree of integration of the remaining crystal orientation, many studies have been made in the past, for example, in Japanese Patent Publication No. 46-23820, after adding Al to steel and hot rolling, A technique is disclosed in which fine AlN is precipitated by hot-rolled sheet annealing at a high temperature of 1000 to 1200 ° C. and the accompanying rapid cooling treatment, followed by rolling under a high-pressure ratio of 80 to 95%. _Ten As a result, a very high magnetic flux density value of 1.95 T is obtained. This method utilizes the fact that finely dispersed and precipitated AlN has a strong action as an inhibitor that suppresses the growth of primary recrystallized grains, and by recrystallizing only nuclei with excellent crystal orientation, An excellent product crystal structure is obtained. However, in this method, since the crystal grain size of the product is generally coarsened, it is difficult to reduce the iron loss, and it is difficult to stably obtain a product having a high magnetic flux density and a low iron loss. Furthermore, the inclusion of Al that is easily oxidized makes it extremely difficult to generate a subscale in the decarburization annealing and a forsterite film in the finish annealing.
[0005]
In Japanese Patent Publication No. 58-42244 and Japanese Patent Publication No. 60-55570, steels containing 0.0003% to 0.0035% B and 0.0030% to 0.0070% N by weight are used, respectively. By setting S to 1.8 or less or 2.1 or less, B ₈ A technique for obtaining a magnetic flux density of 1.85 T to 1.92 T is disclosed. Although this method using BN as an inhibitor has a possibility of obtaining a high magnetic flux density, it not only leads to an increase in cost because Mn is lowered, but it is also difficult to industrialize because it causes hot cracking in the hot rolling process.
[0006]
Further, Japanese Patent Publication No. 7-68581 discloses a technique for reducing the necessary B amount to 0.0018% or less to make Mn / S 1.8 or more, or 2.5 or more, but the magnetic flux density is lowered. Furthermore, in Japanese Patent Application Laid-Open No. 57-114615, the remaining N amount excluding the equivalent amount of N necessary for precipitation of B as BN is defined as the dissolved N amount, and this is made 0.0020% or less. Although it has been disclosed that a high magnetic flux density can be obtained even when Mn / S is 2.1 or more, it has not been possible to stably obtain a grain-oriented electrical steel sheet having a good secondary recrystallization structure.
[0007]
In order to solve this problem, Japanese Patent Application Laid-Open No. 10-140243 discloses that the precipitation of the inhibitor is uniformly refined by controlling the rolling reduction and rolling end temperature in hot finish rolling based on the B content. However, in actual operation, it has been difficult to stably obtain a high magnetic flux density in the entire product.
[0008]
[Problems to be solved by the invention]
This invention pays attention to the superiority in the improvement of the magnetic flux density of the grain-oriented electrical steel sheet containing BN as the main inhibitor, and further increases the degree of integration of crystal orientation to provide an electrical steel sheet with high magnetic flux density and low iron loss. It aims at proposing the manufacturing method which can be obtained stably.
[0009]
[Means for Solving the Problems]
The inventors diligently studied the influence of BN and precipitates containing BN in the steel slab on the secondary recrystallization in order to eliminate the instability of secondary recrystallization that occurs when BN is used as an inhibitor. did. As a result, when a very small amount of Al that is not considered effective for secondary recrystallization is contained together with B, and the steel slab is produced by continuous casting, the ratio of columnar crystals is controlled by controlling the cooling rate and the like. By controlling the heating time and soaking time after heating at a high temperature of 1350 ° C or higher, fine precipitation due to solid solution of the precipitate and subsequent annealing is promoted. It is possible to maintain the grain growth suppression effect of crystal grains, obtain a very advantageous suppression force against the growth of secondary recrystallization, and achieve a high degree of magnetic properties stably. A completely different idea was obtained and used to complete the present invention.
[0010]
In particular,
C: 0.03-0.10 wt%
Si: 2.5-4.5 wt%
Mn: 0.05 to 1.5 wt%,
B: 0.0010 to 0.0060 wt%,
N: 0.0030 to 0.010 wt%,
One or two of S and Se: 0.010 to 0.040 wt%,
And the following formula for the amount of Mn, S, and Se
Mn (wt%) / (S (wt%) + Se (wt%)) ≧ 2.5
Casting continuous casting slab for electrical steel sheet that satisfies
After carrying out hot rolling after heating and soaking the continuous cast slab, cold rolling is performed once or twice or more with intermediate annealing in between to obtain a cold-rolled sheet having a final thickness. In the method for producing grain-oriented electrical steel sheet, after performing decarburization annealing that also serves as primary recrystallization, and then performing final finish annealing to perform secondary recrystallization and purification treatment,
Before casting the continuous cast slab, Al: 0.0010 to 0.0080 wt% is further included, and the columnar crystal ratio in the continuous cast slab is 40% or more,
Furthermore, after the slab heating temperature is set to 1350 ° C or higher, the temperature rising time from 1250 ° C to the heating temperature range is set within 1 hour,
Subsequent slab soaking time t (min) is
1/5 × (1450-T) ≦ t ≦ 2/5 (1500-T)
(T: Slab heating temperature (° C))
By setting it as the range which satisfy | fills, a directional electrical steel sheet with a high magnetic flux density and a low iron loss is manufactured.
[0011]
In addition, the continuous cast slab can be further stabilized by containing one or more selected from Cu, Sb, Sn, Bi, and Mo as an inhibitor element in a range of 0.005 to 0.30 wt%. A high magnetic flux density low iron loss directional electrical steel sheet is manufactured.
[0012]
Further, in the present invention, at the time of final cold rolling, at least one pass is warm-rolled at 100 to 350 ° C., or an aging treatment between passes is performed at 100 to 350 ° C. for 10 to 60 minutes. Thus, a grain-oriented electrical steel sheet having a higher magnetic flux density and lower iron loss can be obtained.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
About the Al which exists in a trace amount, the refinement | miniaturization effect with respect to the precipitate in a steel slab and the appropriate range of Al became clear from the following experiment.
[0014]
(Experiment 1)
In order to clarify the effect of a small amount of Al in the steel containing BN on the primary recrystallized grain growth inhibiting effect and the slab structure, the following experiment was conducted.
[0015]
The composition of the experimental material is as follows.
Experimental material a. Contains C: 0.070 wt%, Si: 3.25 wt%, Mn: 0.07 wt%, B: 0.0020 wt%, N: 0.0085 wt%, Se: 0.018 wt%, Sb: 0.023 wt%, the remainder being inevitable impurities And a basic component composed of iron and iron, and steel containing Al: 0.0010 wt%, 0.0030 wt%, 0.0060 wt%, 0.0080 wt%, and 0.0100 wt% respectively changed to the basic component were used.
[0016]
When continuously casting steel slabs having the above compositions, slabs with columnar crystal ratios of 30% and 60% were produced by changing the molten steel temperature and controlling the cooling during casting. Each slab was heated to 1300 ° C and 1400 ° C, and then hot-rolled to obtain a hot-rolled sheet with a thickness of 2.2 mm, followed by hot-rolled sheet annealing at 900 ° C for 2 min, and then to a thickness of 1.5 mm. After cold rolling and intermediate annealing at 1000 ° C. for 1 min, final cold rolling was performed to obtain a cold rolled sheet of 0.22 mm.
[0017]
Each of the above materials was subjected to decarburization annealing at 830 ° C. for 2 min, and decarburized to C: 0.002 wt% or less. Next, an annealing separator mainly composed of MgO is applied to each sample subjected to such decarburization annealing and heated from 850 ° C. to 1200 ° C. at a rate of temperature increase of 20 ° C./h for final finish annealing. Went. Tables 1 and 2 show the magnetic properties and secondary recrystallization of the obtained electrical steel sheet.
[0018]
[Table 1]

[0019]
[Table 2]

[0020]
First, when the columnar crystal ratio is 30%, secondary recrystallization occurs in some cases. ₈ Is less than 1.9 T. Next, even when the columnar crystal ratio becomes 60%, if the heating temperature is 1300 ° C, the secondary recrystallization is not complete, and the magnetic flux density B ₈ Is low. When the columnar crystal ratio is 60% and the heating temperature is 1400 ° C, both are B compared to the heating at 1300 ° C. ₈ Is rising. However, when Al is not included, secondary recrystallization occurs, but part of the secondary recrystallization is incomplete, so B ₈ Is low and does not reach 1.9T. However, when Al is in the range of 0.001 to 0.008 wt%, secondary recrystallization is complete and B ₈ Was found to yield 1.9 T or more.
[0021]
Furthermore, using these decarburized annealing plates, isothermal annealing for 24 hours at 900 ° C. was performed in an Ar atmosphere.
For each of the samples obtained as a result of the above test,
(1) Primary recrystallized grain size after decarburization annealing (by circle approximation; the same applies below)
(2) Primary recrystallized grain size after isothermal annealing at 900 ° C for 24 h (this corresponds to the primary recrystallized grain just before the start of secondary recrystallization)
Was measured and investigated. The result is shown in FIG.
[0022]
First, for a sample having a columnar crystal ratio of 60%, the primary recrystallized grain size (folded line c) after decarburization primary recrystallization when heated to 1300 ° C. before hot rolling is the inclusion of Al with respect to the basic component. Even when the amount was increased, no significant change in the crystal grain size was observed. The grain size after holding these decarburized annealed plates at 900 ° C. for 24 hours, that is, the primary recrystallized grain size (polygonal line d) immediately before the start of secondary recrystallization is the same for any Al content. did.
[0023]
On the other hand, when the heating before hot rolling is 1400 ° C., the primary recrystallized grain size (folded line a) after decarburization primary recrystallization decreases as the Al content increases, and Al decreases to 0.006 wt%. From around the time it grew again. In the case where Al is not contained, the particle size after being kept at 900 ° C. for 24 hours is coarsened. However, when the Al content is in the range of 0.001 wt% to 0.008 wt%, the coarsening of the particle size is suppressed. I found out.
[0024]
Next, FIG. 1 shows only a sample heated at 1400 ° C. with a columnar crystal ratio of 30%. In these samples, the primary recrystallized grain size is considerably coarsened after annealing for 24 hours, even though the heating temperature was increased to 1400 ° C.
[0025]
As a result of intensive studies on the cause of the above results, the inventors have studied that the columnar crystal ratio is 60% and the Al content is 0.001 with the coarsening of the primary recrystallization grain size immediately before the secondary recrystallization suppressed. In the case of -0.008 wt%, it became clear that the solid solution at the time of heating before hot rolling was good. Details are described below.
[0026]
Each slab having the composition of the above-mentioned experimental material a was heated to 1300 ° C. and 1400 ° C., respectively, and then quenched with water. As a result of examining the slab before and after heating in detail with an optical microscope and an electron microscope, a large number of precipitates were confirmed. When the constituents of these precipitates were analyzed, B and N as inhibitor components were detected.
Tables 1 and 2 also show the results of observing the presence or absence of precipitates after heating when changing the slab heating conditions before hot rolling and the amount of Al added to the material.
[0027]
From this result, when the heating temperature is 1300 ° C. and when the heating temperature is 1400 ° C. with a columnar crystal ratio of 30%, residual precipitates are confirmed at any Al content. In addition, when the columnar crystal ratio was 60% and the heating temperature was 1400 ° C., residual precipitates were confirmed when Al was not included. Nothing was observed.
[0028]
Next, for the material not containing Al and the material containing 0.006 wt% of Al among the slabs of the composition a, the particle size of each precipitate observed before heating is measured by an image analyzer, The distribution of the precipitate particle size and the average particle size of the precipitate were determined. This is shown in FIG. First, with regard to the material with a columnar crystal ratio of 60%, the steel containing no Al (Fig. 2a) has a wide distribution of precipitate particle size and many coarse precipitates exceeding 10 μm, and its average particle size is also 7.74 μm. It is getting bigger. On the other hand, the steel containing Al (Fig. 2b) has few coarse precipitates exceeding 10 µm, the average particle size is 5.65 µm, and it is clear that the precipitates are relatively fine. It was.
[0029]
Next, in the material having a columnar crystal ratio of 30%, even when Al is contained at 0.006% (Fig. 2c), there are many coarse precipitates exceeding 10 µm, and the average particle size is also large at 7.16 µm. . Regarding the precipitated particles in this slab, it was found that the columnar crystal part has a large number of particles of 10 μm or less, but the equiaxed crystal part has more particles of 10 μm or more, which has increased the average particle size. .
[0030]
Therefore, in the samples No. 20 to 23 in Table 1, the inhibitor component is finely precipitated for the first time by increasing the columnar crystal ratio, that is, by quenching and quenching rapidly and further containing Al in the range of 0.001 to 0.008 wt%. Further, it is considered that the solid solution of the precipitate was promoted by further increasing the heating temperature to 1400 ° C., and as a result, the remaining precipitate was not observed.
[0031]
In this way, the relatively finely precipitated inhibitor component is completely dissolved once, and further finely re-precipitated in a later step, so that coarsening of the primary recrystallized grains immediately before the secondary recrystallization is suppressed, and strong grains It is thought that the effect of growth suppression was expressed.
[0032]
(Experiment 2)
In Experiment 1, stabilization of secondary recrystallization and good magnetic properties were obtained by adding Al to the steel containing B and N. Therefore, the magnetic characteristics were investigated when Al was added in the same range as in Experiment 1 without adding B.
[0033]
The composition of the experimental material is as follows.
Experimental material b. Contains C: 0.070 wt%, Si: 3.23 wt%, Mn: 0.07 wt%, N: 0.0080 wt%, Se: 0.020 wt%, Sb: 0.025 wt%, with the remainder consisting of inevitable impurities and iron Components and steels containing Al: 0.0010 wt%, 0.0030 wt%, 0.0060 wt%, 0.0080 wt%, and 0.0100 wt% in each of the basic components were used.
[0034]
When producing a continuous cast slab having the above-mentioned composition, the columnar crystal ratio is set to 60%, this is heated to 1400 ° C, then hot rolled into a hot rolled sheet having a thickness of 2.6 mm, and heated at 950 ° C for 2 min. After the sheet annealing, it was cold-rolled to a thickness of 1.8 mm, and after intermediate annealing at 1050 ° C. for 1 min, the final cold-rolling was performed to obtain a 0.34 mm cold-rolled sheet. The cold-rolled sheet was decarburized and annealed at 840 ° C. for 3 min to decarburize to C: 0.002% or less. An annealing separator containing MgO as a main component was applied to each of these samples, and finish annealing was performed by heating from 850 ° C. to 1200 ° C. at a rate of 15 ° C./h. Table 3 shows the magnetic properties and coating appearance of the obtained electrical steel sheet.
[0035]
[Table 3]

[0036]
From the above results, it was confirmed that the secondary recrystallization did not occur and the magnetic properties were deteriorated only by the addition of Al. It was also found that when the Al content was increased, the coating appearance changed to whitish and deteriorated.
[0037]
(Experiment 3)
Contains C: 0.068 wt%, Si: 3.24 wt%, Mn: 0.07 wt%, B: 0.0040 wt%, N: 0.0075 wt%, Se: 0.019 wt%, Sb: 0.025 wt%, Al: 0.0060 wt% In addition, a slab having a columnar crystal ratio of 45% manufactured by continuous casting was prepared for steel composed of unavoidable impurities and iron. After slab heating with various heating times up to 80 min in the range of 1300 to 1425 ° C, hot rolled to a hot rolled sheet with a thickness of 2.2 mm, and hot rolled sheet annealing at 900 ° C for 2 min, It was cold-rolled to a thickness of 1.5 mm, subjected to intermediate annealing at 1000 ° C. for 1 min, and then finally cold-rolled to obtain a 0.22 mm cold-rolled sheet. These cold-rolled sheets were decarburized and annealed at 830 ° C. for 2 min and decarburized to C: 0.002% or less. An annealing separator mainly composed of MgO was applied to each of these samples, and finish annealing was performed by heating from 850 ° C. to 1200 ° C. at a rate of 20 ° C./h. The quality of the magnetic properties of the obtained electrical steel sheet is shown in FIG. In FIG. 3, the circles indicate the magnetic flux density B ₈ Indicates that the magnetic flux density is less than 1.9 T.
[0038]
From this figure, the slab heating time t (min) is determined by the heating temperature T (° C.),
1/5 × (1450-T) ≦ t ≦ 2/5 × (1500-T)
It was clarified that a material having a high magnetic flux density can be obtained within a range satisfying the above.
[0039]
Although the important point concerning this invention was invented above, embodiment of this invention is described concretely below.
(Chemical composition)
C: 0.03-0.10wt%
If the amount of C exceeds 0.10 wt%, the amount of γ transformation becomes excessive, and the distribution of B during hot rolling becomes non-uniform, which is harmful as a result of inhibiting the uniformity of the distribution of BN. Moreover, the load of decarburization annealing increases and it becomes easy to generate | occur | produce a decarburization defect. On the other hand, if it is less than 0.03 wt%, the secondary recrystallization is incomplete and the magnetic properties are also deteriorated. Therefore, C is limited to the range of 0.03 to 0.10 wt%.
[0040]
Si: 2.5 to 4.5 wt%
Si is an essential component for increasing electrical resistance and reducing iron loss.For this reason, it is necessary to contain 2.5 wt% or more, but if it exceeds 4.5 wt%, the workability deteriorates and rolling or Since processing of the product becomes extremely difficult, the range is 2.5 to 4.5 wt%.
[0041]
Mn: 0.05-1.5 wt%
Mn is also a necessary component because it increases electrical resistance and improves hot workability during production. For this purpose, it is necessary to contain 0.05 wt% or more. However, if it exceeds 1.5 wt%, the gamma transformation is induced and the magnetic properties deteriorate, so the range of 0.05 to 1.5 wt% To do.
[0042]
B and N:
In the present invention, BN is used as a main inhibitor component for the stable generation of subscales and thereby the formation of a good undercoat. In particular, when the final cold rolling reduction is 80% or more, the secondary recrystallization temperature becomes very high. Therefore, it is essential to contain B and N as inhibitor components that are stable at high temperatures in the steel. Among these, B is contained in the range of 0.0010 to 0.0060 wt%. If the B content is less than 0.0010 wt%, the amount of precipitated BN is insufficient and good secondary recrystallization cannot be obtained. If it exceeds 0.0060 wt%, the solid solution temperature increases and normal heating is performed. This is because it becomes impossible to completely dissolve BN before hot rolling. The N content needs to be 0.0030 wt% or more. If the N content is less than 0.0030 wt%, the amount of BN that precipitates is insufficient. If the N content exceeds 0.010 wt%, gasification occurs in the steel and defects such as blistering occur, so the range is 0.0030 to 0.010 wt%.
[0043]
Auxiliary inhibitor components:
As an inhibitor component for assisting B and N, Se and S need to be contained alone or in combination. Since these components precipitate in the steel as Mn compounds or Cu compounds, a total amount of 0.010 wt% or more is necessary to maintain the suppression effect, but if it exceeds 0.040 wt%, the slab heating temperature will be extremely high. However, it cannot be completely dissolved, and remains as a coarse precipitate, which is harmful. Therefore, the range is 0.010 to 0.040 wt%. In relation to the amount of Mn, if the value of Mn (wt%) / (S (wt%) + Se (wt%)) is less than 2.5, intergranular cracks and ear cracks increase significantly during hot rolling. It is practically necessary to satisfy Mn / (S + Se) ≧ 2.5.
[0044]
Other inhibitor elements:
Cu, Sb, Sn, Bi, and Mo have an auxiliary role of enhancing the suppressive force as inhibitors, and can be added as necessary. A preferable range of these addition amounts is 0.005 to 0.30 wt%. In addition, addition of Ni and Co improves the surface properties of the steel sheet, so it may be added as appropriate.
[0045]
Al: 0.0010 to 0.0080 wt%
In the present invention, secondary recrystallization is stabilized by the addition of a small amount of Al, and good magnetic properties are obtained. Al is known as an inhibitor element because it forms AlN, but it is presumed from the above experimental results that the effects of improving the stability and magnetic properties of secondary recrystallization were observed. It is considered that the precipitation behavior of BN or Mn (Se + S) was changed by adding a small amount of Al. One is presumed that the precipitation temperature was lowered due to the presence of Al during continuous casting, resulting in uniform fine precipitation, and the other was the formation of composite precipitate particles during heating, thereby suppressing Ostwald growth and suppressing coarsening. .
[0046]
This addition of Al facilitates solid solution by making the precipitate finer before heating the slab, and as a result of the finer reprecipitation of the inhibitor after hot rolling, the ability to suppress the growth of primary recrystallized grains is increased. It is thought that finally good magnetic properties were obtained.
When the added amount of Al is less than 0.0010 wt%, the above effect cannot be obtained. When the added amount exceeds 0.0080 wt%, the secondary recrystallized grain size becomes coarse and the iron loss deteriorates. For these reasons, the amount of Al needs to be in the range of 0.0010 to 0.0080 wt%.
[0047]
Moreover, when Al is added in a large amount, there is an aspect that it is difficult to generate subscales during decarburization annealing and forsterite generation during finish annealing. Due to such deterioration of the coating, not only the appearance of the coating but also the magnetic properties are deteriorated. In order to prevent these deteriorations, it is necessary to limit Al to 0.0080 wt% or less.
The reason why such an appropriate range exists is not clear, but when the amount of solute Al increases, it becomes easier to form oxides near the surface layer of the steel sheet, and forsterite coating in sub-scale generation and finish annealing in decarburization annealing It is considered that adverse effects such as inhibition of the production of selenium appear.
[0048]
(Rolling conditions)
Steel adjusted to the above components is continuously cast into a slab. At this time, it is necessary to increase the ratio of columnar crystals in the structure in the slab. Precipitated particles in the columnar crystal are finer than the equiaxed crystal part, and by increasing this ratio, the solid solution in the subsequent slab heating is improved. Therefore, the columnar crystal ratio needs to be 40% or more.
[0049]
In the subsequent slab heating, it is necessary to set the heating temperature to 1350 ° C or higher. In the present invention, after adding the predetermined amount of Al shown above, the columnar crystal ratio in the slab in continuous casting is set to 40% or more, and the slab heating temperature is set to 1350 ° C. or more for the first time. It becomes possible to completely dissolve Mn (Se + S) once, and a uniform and fine dispersion state of the inhibitor can be obtained by subsequent reprecipitation.
[0050]
Moreover, in slab heating, the coarsening of the precipitated BN becomes a problem. This seems to be derived from the large diffusion coefficient of B. Therefore, the time required for raising the temperature from 1250 ° C. to the target heating temperature is set within one hour, and the soaking time t (min) is determined by the soaking temperature T (° C.) from the above-described experiment. ,
1/5 × (1450-T) ≦ t ≦ 2/5 (1500-T)
(T: Slab heating temperature)
It is necessary to be within the range.
[0051]
In the subsequent hot rolling, known techniques such as thickness reduction processing and width reduction processing for homogenizing the structure before and after slab heating can be added as needed. The hot-rolled sheet obtained by hot rolling is subjected to the hot-rolled sheet annealing after the hot-rolled sheet annealing as required, and the cold-rolled one-time method to make the final sheet thickness by one cold rolling, or as necessary After the application, a cold rolling two-time method in which the first cold rolling and further the second cold rolling with the intermediate annealing interposed therebetween can be adopted. In addition, it is possible to perform cold rolling three or more times with a plurality of intermediate annealings.
[0052]
About the rolling reduction of cold rolling, in the case of the cold rolling twice method as conventionally well-known, the 1st rolling shall be a rolling reduction of 15 to 60%. If the rolling reduction is less than 15%, the rolling recrystallization mechanism does not work, so that the crystal structure cannot be made uniform. If it exceeds 60%, the crystal structure is accumulated and the effect of the second rolling is obtained. It is because it becomes impossible. The rolling reduction of the final rolling is 80 to 90%. This is because when the rolling reduction exceeds 90%, secondary recrystallization becomes difficult, and when it is less than 80%, good secondary recrystallization grain orientation cannot be obtained, and the magnetic flux density of the product deteriorates.
[0053]
In the final cold rolling, warm rolling at 100 to 350 ° C. or aging treatment between passes at 100 to 350 ° C. for 10 to 60 min can further improve the texture of primary recrystallization. Is preferably employed. Further, after the final cold rolling, it is possible to perform a known magnetic domain refinement process, for example, a process of providing a linear groove on the steel sheet surface.
[0054]
The steel sheet having the final thickness by the above process is subjected to decarburization and primary recrystallization annealing by a known method, and an annealing separator containing MgO as a main component is applied to the steel sheet surface and subjected to final finishing annealing. At that time, the addition of a Ti compound, or the inclusion of Ca or B in the annealing separator has the effect of further improving the magnetic properties.
[0055]
In the final finish annealing, at least 900 ° C or higher during the temperature rise ₂ It is necessary to raise the temperature in an atmosphere containing. That is, N up to high temperature ₂ If annealing is performed only in the atmosphere, nitriding occurs during the final finish annealing, and crystal grains with inferior orientation are secondary recrystallized, resulting in deterioration of magnetic flux density.Therefore, the atmosphere during the final finish annealing is at least H above 900 ° C ₂ It is necessary to pass through. H ₂ The atmosphere plays an important role in the formation of oxides and nitrides in the film, and it is thought that it is necessary to increase the reducibility particularly in the middle to late stages of annealing at 900 ° C. or higher.
[0056]
After the final finish annealing, after removing the unreacted annealing separator, an insulating coating is applied to the surface of the steel sheet to make a product, but if necessary, the surface of the steel sheet may be mirrored before applying the coating. The coating baking process can also be used as a flattening process. Furthermore, for the steel sheet after the secondary recrystallization, a known magnetic domain refinement process, that is, a process of applying a plasma jet or laser irradiation to the linear region, or providing a linear dent region by a protruding roll, An effect of reducing iron loss can also be obtained.
[0057]
【Example】
The components shown in Table 4 and the remainder were prepared as a continuous cast slab composed of iron and inevitable impurities.
[0058]
[Table 4]

[0059]
For these continuous cast slabs, two slabs with columnar crystal ratios of 25% and 70% were controlled by controlling the cooling rate, heated from 1250 ° C to 1420 ° C for 50 min, soaked for 15 min, and then heated to a thickness of 2.2 mm. And rolled into a coil at 550 ° C. to obtain a hot rolled sheet. The hot-rolled sheet was subjected to hot-rolled sheet annealing at 1000 ° C. for 60 s, quenched at 20 ° C./s, and finished to a thickness of 1.6 mm by the first cold rolling. The steel sheet was heated to 1050 ° C and subjected to intermediate annealing to hold for 60s, quenched at 40 ° C / s, and subjected to aging treatment at 300 ° C for 30min during cold rolling to a thickness of 0.22mm each. It was. The resulting cold-rolled sheet was degreased and decarburized and annealed at 840 ° C for 2 min, and then MgO was mixed with SrSO _Four 2%, TiO ₂ After applying an annealing separator with 8% added, final finishing annealing was performed. The final finish annealing conditions are N up to 850 ° C. ₂ After raising the temperature at 30 ° C / h, the temperature from 850 ° C to 1200 ° C is 50% N ₂ ・ 50% H ₂ The temperature rises at 20 ° C / h in H ₂ Hold for 8 h and then H up to 600 ° C ₂ Inside, N from 600 ℃ ₂ The temperature was lowered in the atmosphere. After the final finish annealing, the unreacted annealing separator was removed, magnesium phosphate containing 60% colloidal silica was applied as a tension coating, and baked at 840 ° C. to obtain a product. The magnetic properties of the obtained product are shown in Table 5.
[0060]
[Table 5]

[0061]
As is apparent from Table 5, when a grain-oriented electrical steel sheet using BN as an inhibitor is produced, a very high magnetic flux is obtained when a small amount of Al is contained in the material slab and the columnar crystal ratio in the slab is increased. Density and low iron loss characteristics are obtained.
[0062]
(Example 2)
The continuous casting slab which consists of the component shown in Table 6, and the remainder consisting of iron and inevitable impurities was prepared.
[0063]
[Table 6]

[0064]
For these continuous cast slabs, the columnar crystal ratio was 83% by controlling the cooling rate, heated from 1250 ° C to 1400 ° C in 40min, soaked for 35min, hot rolled to 2.6mm thickness, and coiled at 550 ° C A hot rolled sheet was wound into a shape.
The hot-rolled sheet was subjected to hot-rolled sheet annealing at 900 ° C. for 60 s, quenched at 20 ° C./s, pickled, and finished to 1.8 mm by the first cold rolling.
[0065]
Next, the temperature was raised to 1050 ° C., intermediate annealing was performed for 60 s, and quenching was performed at 25 ° C./s. Of the two steel sheets obtained as described above, one sheet was subjected to warm rolling at 250 ° C., and MgO containing 0.5% Ca and 0.09% B was added to SrSO. _Four 4%, TiO ₂ An annealing separator with 7% added was applied, and final finish annealing was performed. The condition for final finish annealing is N up to 850 ° C. ₂ The temperature was raised at 30 ° C / h in the atmosphere, and 25% N from 850 ° C to 1050 ° C. ₂ And 75% H ₂ The temperature was increased at 15 ° C / h in a mixed atmosphere with ₂ The temperature was raised to 1200 ° C at 25 ° C / h in this, kept at 1200 ° C for 8 hours, and then increased to 600 ° C. ₂ After cooling down, N from 600 ℃ ₂ The temperature was lowered in the atmosphere. After such finish annealing, the unreacted annealing separator was removed, magnesium phosphate containing 50% colloidal silica was applied as a tension coating, and baked at 840 ° C. to obtain a product. Table 7 shows the magnetic characteristics of these products.
[0066]
[Table 7]

[0067]
As apparent from Table 7, when producing a grain-oriented electrical steel sheet using BN as an inhibitor, the invention example in which a small amount of Al is contained in the material slab provides an extremely high magnetic flux density and low iron loss characteristics. Moreover, the appearance of the film is also good. Furthermore, when warm rolling is performed during cold rolling, the magnetic properties are further improved.
[0068]
【The invention's effect】
Thus, according to the present invention, it becomes possible to produce a grain-oriented electrical steel sheet having high magnetic flux density and low iron loss while using BN as a main inhibitor, and as a result, it is possible to achieve both good film properties and high magnetic flux density. Thus, the iron loss value can be further reduced as compared with the conventional case.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between Al content and primary recrystallized grain size in a basic experiment leading to the present invention.
FIG. 2 is a graph showing the difference in precipitate distribution depending on the presence or absence of Al in a basic experiment leading to the present invention.
FIG. 3 is a graph showing quality of magnetic characteristics with respect to slab heating temperature and heating time in a basic experiment leading to the present invention.

Claims (3)

C: 0.03-0.10 wt%
Si: 2.5-4.5 wt%
Mn: 0.05 to 1.5 wt%,
B: 0.0010 to 0.0060 wt%,
N: 0.0030 to 0.010 wt%,
One or two of S and Se: 0.010 to 0.040 wt%,
And the following formula for the amount of Mn, S, and Se
Mn (wt%) / (S (wt%) + Se (wt%)) ≧ 2.5
Casting continuous casting slab for electrical steel sheet that satisfies
After carrying out hot rolling after heating and soaking the continuous cast slab, cold rolling is performed once or twice or more with intermediate annealing in between to obtain a cold-rolled sheet having a final thickness. In the method for producing grain-oriented electrical steel sheet, after performing decarburization annealing that also serves as primary recrystallization, and then performing final finish annealing to perform secondary recrystallization and purification treatment,
Before casting the continuous cast slab, Al: 0.0010 to 0.0080 wt% is further included, and the columnar crystal ratio in the continuous cast slab is 40% or more,
Furthermore, after the slab heating temperature is set to 1350 ° C or higher, the temperature rising time from 1250 ° C to the heating temperature range is set within 1 hour,
Subsequent slab soaking time t (min) is expressed by the following formula 1/5 × (1450-T) ≦ t ≦ 2/5 (1500-T)
(T: Slab heating temperature (° C))
Method for producing oriented electrical steel sheets towards you, characterized in that the range satisfying. The continuous cast slab further contains one or more selected from Cu, Sb, Sn, Bi, and Mo as an inhibitor element in a range of 0.005 to 0.30 wt%, respectively. method of manufacturing oriented electrical steel sheet towards. The final cold rolling is characterized in that at least one pass is warm-rolled at 100 to 350 ° C, or an aging treatment between passes is performed at 100 to 350 ° C for 10 to 60 minutes. or method for producing oriented electrical steel sheet towards the description.

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