JP4123679B2 - Method for producing grain-oriented electrical steel sheet - Google Patents

Description

【００１８】
【表２】

【００１９】
表２に示したとおり、Bi添加鋼においては、従来から管理されてきた仕上げ入側温度やコイル巻取り温度などよりも、むしろスラブ加熱時における雰囲気や熱間圧延時の時間および熱延板の表面と中心部との温度差といった、従来あまり管理されていなかった項目がある一定条件で組み合わされた時に、良好な被膜特性と磁気特性が得られることが判明した。
【００２０】
上記の実験において、被膜特性が良好となった理由は、熱延工程でその表面が改質されたためと考えられる。
そこで、スラブ加熱時における加熱温度と雰囲気の酸素濃度がスラブ表面に及ぼす影響を明らかにするために、次の実験を行った。
供試鋼成分として、Ｃ：0.05％, Si：3.15％, Mn：0.055％, Bi：0.015％, Al：0.022％, Ｎ：0.0075％およびＳ：0.020 ％を含有し、残部は Fe および不可避的不純物の組成になる鋼を、連続鋳造によってスラブとしたのち、 100mm×100mm ×100mm のサンプルを切り出した。
このサンプルを、加熱雰囲気中の酸素濃度と加熱温度を種々に変化させて、３時間均熱炉に装入した。
その後、地鉄表層のBi量を蛍光Ｘ線を用いて測定した結果を、加熱雰囲気中の酸素濃度との関係で図１に示す。
【００２１】
同図に示したように、ある特定範囲すなわち、加熱雰囲気中の平均酸素濃度が100 ppm 以上で、かつ加熱温度が1125℃以上の場合に、地鉄表層のBi量が母材のそれに比べて 1/2以下まで低減することが明らかとなった。
また、加熱雰囲気中の平均酸素濃度が 50000 ppmを超える加熱では、表面から５mm深い箇所でもBi濃度が中心部のそれの 1/2以下まで低減することが判明した。
【００２２】
次に、スラブ加熱時における加熱温度と加熱時間の関係を明らかにするために、雰囲気中の酸素濃度は 2000ppmの一定とし、加熱温度と加熱時間を種々に変化させた場合における地鉄表層のBi量について調査した。
得られた結果を図２に示す。
同図に示したとおり、1125℃以上の温度で、１時間以上加熱することによって、表面のBi濃度は中心部のそれの1/2 以下まで低減することが判明した。
【００２３】
上記のようなスラブ加熱処理によって、被膜特性と磁気特性が改善される理由は、次のように考えられる。
すなわち、Biは、鉄に対する固溶量が非常に少ないため、鋼を連続鋳造でスラブとした場合、極めて均一に分散し、スラブ表層にも板厚中心部と同じ濃度でBiが存在する。このため、二次再結晶焼鈍時に表面層に存在するBiがフォルステライトの生成を阻害し、著しい被膜欠陥を引き起こすと共に、被膜欠陥により気相雰囲気が鋼中に過度の作用をもたらし、鋼中のインヒビターの分解挙動が大きく変動して、正常な二次再結晶が生じなくなる。また、二次再結晶焼鈍は通常、コイル状に巻いて行うため、鋼板の幅方向、長手方向で気相雰囲気との接触の仕方が異なり、場所によって被膜形成と二次再結晶のあり方が変化することから、均一な製品を作ることが極めて困難となる。
【００２４】
従って、表層のBi濃度は、インヒビター強度に影響を及ぼさない範囲で低下させる必要があると考えられる。
すなわち、前掲図１，２に示したように、スラブ加熱を、平均酸素濃度が 100〜50000 ppm の雰囲気中にて、1125℃以上の加熱温度で１時間以上行うことによって、表面に存在するBiをスケールと共に除去することが重要である。なお、この際、必要以上の高温保持は表面層のみならず内部のBi濃度も低下するので、好ましくない。
【００２５】
また、熱間圧延によって板厚を減じる際は、表層からの過剰なBiの散逸を防止するため、表層の温度を中心より常に低く保持することが重要と考えられる。
すなわち、熱間圧延中は、圧延により鋼中に転位が多量に導入されるため、拡散係数が非常に高くなるが、表層の温度を低下させてやれば、表面での拡散速度を中心層に対して遅くすることができ、その結果、中心層からのBiの拡散を抑えることができるものと考えられる。
【００２６】
さらに、熱間圧延時間に要する時間を所定の範囲に制限することによって、Bi濃度を適切に制御することができ、これにより板厚中心部に一定濃度以上のBi濃度を確保することで、二次再結晶時に必要な抑制力を確保することが可能となる。
かくして、従来のBi添加による２次再結晶の不安定性が解消され、被膜特性の改善と磁気特性の安定化の両立が可能になったものと考えられる。
【００２７】
次に、発明者らは、Bi添加材のフォルステライト被膜生成を如何にして改善するかについて鋭意研究を重ねた結果、鋼中へのCr添加が極めて有効であることを見出した。
以下、この知見事実を、Crの添加量を変更しつつ、Biとの複合添加について行った実験結果に基づいて説明する。
Ｃ：0.05％, Ni：0.10％, Si：3.30％, Mn：0.06％, Se：0.014 ％, Sb：0.045 ％, Bi：0.025 ％, Al：0.027 ％, Ｎ：0.0095％, Cu：0.09％およびSn：0.1％をベースとし、Crをそれぞれ 0.03, 0.05, 0.15, 0.2, 0.5, 0.7％含有させたスラブを作製した。
かかるスラブを、酸素濃度：500ppmの雰囲気中にて1200℃で２時間加熱後、電気式加熱炉にて1400℃で１時間の加熱を酸素濃度：1500 ppmの雰囲気で行った。その後、粗圧延の１パス目を表面温度：1350℃、中心温度：1360℃で圧下率：50％、ついで２パス目を表面温度：1300℃、中心温度：1320℃で圧下率：35％、３パス目を表面温度：1250℃、中心温度：1290℃で行ったのち、仕上げ圧延を、入側表面温度：1100℃、中心温度：1120℃で、かつ、出側表面温度：990 ℃、中心温度：995 ℃で行い 2.2mm厚の熱延板としたのち、巻取り温度：575 ℃でコイルに巻き取った。
【００２８】
ついで 950℃で２分間の均熱後、 300℃までは平均速度：25℃/sで冷却する熱延板焼鈍を行ったのち、酸洗し、1.5 mmまで冷間圧延した。引き続き1070℃で１分間の中間焼鈍後、 250℃の温間圧延を含む冷間圧延により0.22mmの板厚としたのち、 840℃で２分間の脱炭焼純を施した。
その後、MgＯを主成分とする焼純分離剤を塗布してから、窒素雰囲気で 850℃まで10℃/hで昇温し、15時間の保定焼鈍を行ったのち、窒素：25 vol％と水素：75 vol％の雰囲気中で1200℃まで30℃/hの昇温速度で加熱する仕上げ焼鈍を行った。
かくして得られた製品板の磁気特性および被膜特性について調べた結果を表３に示す。
なお、被膜特性は、40％のコロイダルシリカを含有するリン酸マグネシウムをコート剤として塗布し、850 ℃で焼付けたのち、丸棒に巻付ける屈曲試験により被膜の剥離限界直径で評価した。
【００２９】
【表３】

【００３０】
表３から明らかなように、Crを0.05％以上添加することにより、熱延における表層Biの低減処置に加えて、より一層の被膜改善効果が認められた。
このような良好な被膜の生成は、二次再結晶中での気相雰囲気との相互作用を適切なものとし、磁気特性の向上効果も達成される。また、フォルステライトが鋼板へ張力を付与するため鉄損の改善にも大きく寄与している。
なお、Crの効果については必ずしも明らかではないが、Cr添加した素材では脱炭焼鈍板のサブスケールの構造が変化し、二次再結晶焼鈍中のMgＯとの反応が効果的に促進されるためと考えられる。
しかしながら、過剰のCr添加は磁束密度の低下を招く。
【００３１】
次に、本発明に従う、方向性電磁鋼板の好適製造条件について説明する。
まず、素材成分について述べる。
Si：2.5 〜4.5 ％
Siは、電気抵抗を増加させて鉄損を低減するために不可欠の元素であり、このためには 2.5％以上の含有が必要であるが、4.5 ％を超えると加工性が劣化し、製造そのものや、製品の加工が極めて困難になるので、Si量は 2.5〜4.5 ％の範囲に限定した。
【００３２】
0.03≦Ｃ＋(Ni/30) ≦0.10％
ＣとNiの含有量を（Ｃ＋Ni/30)の式で0.10％以下とすることが、本発明の特徴である。
というのは、（Ｃ＋Ni/30)が0.10％を超えるとγ変態量が過剰となり、熱間圧延中に析出するMnSe、MnＳなどのインヒビターの分布の均一性が阻害される。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不利もある。一方（Ｃ＋Ni/30)が0.03％未満では組織改善効果が得られず、２次再結晶が不完全となり、同じく磁気特性が劣化する。従って、ＣとNiは、単独または複合含有いずれの場合においても（Ｃ＋Ni/30)式で0.03〜0.10％の範囲に限定した。
【００３３】
Bi：0.005 〜0.05％
Biの添加は、本発明の特徴の一つである。ここに、Bi量が 0.005％未満では、上記したような期待する効果が得られず、一方0.05％を超えると均一分散が困難となるので、Biは 0.005〜0.05％の範囲で含有させるものとした。
なお、このBiは、酸化反応を強く抑制し、脱炭焼鈍板に形成されるSiO₂の形態を大きく変えてしまうため、従来技術の延長では被膜生成が困難になると予想された元素である。
【００３４】
Mn：0.05〜1.5 ％
Mnも、Siと同様、電気抵抗を高めて鉄損を低減させるだけでなく、製造時の熱間加工性を向上させる点でも有用な元素である。この目的のためには0.05％以上の含有が必要であるが、1.5 ％を超えて含有させた場合、γ変態を誘起して磁気特性が劣化するので、Mn量は0.05〜1.5 ％の範囲に限定した。
【００３５】
インヒビター元素については、次のとおりである。
Ｓ, Se：0.010〜0.040 ％または 0.010％未満
インヒビター成分として、Se, Ｓを単独または複合して含有させることができる。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が、抑制効果を維持するには合計で 0.010％以上含有させる必要があるが、 0.040％を超えると高温のスラブ加熱でも完全に固溶させることができず粗大な析出物となり、かえって有害となるので、 0.010〜0.040 ％の範囲に限定した。
一方、高温のスラブ加熱を省略する場合には、Se, Ｓは少ないほど固溶温度が低下するため好適に作用する。従って、その場合には、両者併せて 0.010％未満とする。
【００３６】
sol.Al：0.015 〜0.050 ％およびＮ：0.005 〜0.015 ％
最終冷延圧下率が80％以上の場合、２次再結晶温度が非常に高くなるため、鋼中にはこれらの元素の他に高温で安定なインヒビター成分の含有が必要で、かようなインヒビター成分としては、AlおよびＮが好適である。
このうち、Alはsol.Al (酸可溶Al) として 0.015〜0.050 ％含有させる必要がある。というのは、sol.Al量が 0.015％未満の場合、析出するAlＮの量が不足して良好な２次再結晶を得ることができず、一方 0.050％を超えるとインヒビターとして機能するサイズへの均一分散が困難となるからである。
また、Ｎは、0.005 ％以上の含有を必要とするが、0.015 ％を超えて含有させると鋼中でガス化しフクレなどの欠陥をもたらすので、Ｎは 0.005〜0.015 ％の範囲で含有させるものとする。
【００３７】
また、インヒビター補強元素については次のとおりである。
すなわち、Cu, Sn, Sb, Mo, As, Te, ＰおよびＢ等は、公知のインヒビターの抑制力を強化する補助的働きを有するので、鋼中に随時添加することが好ましい。このために必要な好適添加量については、Cu, Snは0.05〜0.5％、Sb, As, Mo, Te, Ｐは0.005〜0.10％、Ｂは0.0010〜0.01％である。
その他の添加元素については、例えばGe, Co等は、鋼板の表面性状を改善する効果があるので適宜含有させることが好ましい。
【００３８】
Cr：0.05〜0.50％
上述したとおり、Biは、酸化反応を強く抑制し、脱炭焼鈍板に形成されるSiO₂の形態を大きく変えてしまうため、従来技術では被膜生成が困難とされた元素であった。
しかしながら、適量のCrを併せて含有させると上記の問題を解消することができる。
今回、Crを複合添加することで被膜生成が可能となったのは、CrがBiの酸化抑制効果を打ち消して脱炭焼鈍板のSiO₂形態を良好に改善する効果を持つためか、あるいはフォルステライト生成反応を促進するためか、さらには両方の効果を有すためと考えられる。ここに、含有量が0.05％未満ではその添加効果に乏しく、一方0.50％を超えても被膜改善効果は飽和し、むしろコスト高となり、しかも磁束密度が低下する傾向があるので、Cr量は0.05〜0.50％の範囲に限定した。
【００３９】
次に、本発明に従う製造条件について具体的に説明する。
上述した好適成分組成に調整された溶鋼は、通常、連続鋳造法または造塊−分塊法によってスラブとする
ついで、このスラブは、通常スラブ加熱に供されたのち、熱間圧延により熱延コイルとされるが、この時スラブ加熱温度を1350℃以上とすることが重要である。というのは、スラブ加熱温度が1350℃に満たないとインヒビターの固溶が十分でなく、Mn（Se＋Ｓ) ，AlＮ等の微細均一な分散析出状態が得られないからである。
一方、SeやＳのように溶体化に高温を必要とする組成を制限し、高温のスラブ加熱を省略する方法では、スラブ加熱温度は、粒成長が生じない1250℃以下とすることが、熱延組繊の均質化ひいては磁気特性の改善の面で効果的である。
なお、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の公知の技術を随時加えることは有効である。
【００４０】
本発明の特徴である熱間圧延は、スラブ加熱を平均酸素濃度 100〜50000 ppmの雰囲気中にて1125℃以上の温度で１時間以上行うことにより、表面に存在するBiをスケールと共に加熱炉内で剥離除去することである。
この際、10時間以上の高温保持は、表面層だけでなく内部までBi濃度が低減するので好ましくない。
また、熱間圧延により板厚を減じる際は、表層からの過剰なBiの散逸を防止するため、表層の温度を中心より常に低く保ち続ける必要がある。また、熱間圧延中は、圧延により鋼中に転位が多量に導入され、拡散係数が非常に高くなっているので、この面でも、表層の温度を低下して、表面での拡散速度を中心層よりも遅くしておけば、中心層からのBiの拡散を抑えることができる。
さらに、熱間圧延時間に要する時間を30〜300 秒に制限することによって、Bi濃度を適切に制御することができ、これにより板厚中心部に一定濃度以上のBi濃度を確保することができるので、二次再結晶時に必要な抑制力を確保することが可能となる。
かくして、従来、Biを添加する場合に懸念された２次再結晶の不安定性が解消され、磁気特性の安定化が可能となる。
【００４１】
冷延工程については、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、または必要に応じて熱延板焼鈍を施したのち、中間焼鈍を挟む２回以上の冷間圧延を施す冷延２回法を採用できる。
冷間圧延の圧下率については、従来公知なように冷延２回法の第１回目の圧延は15〜60％程度とすることが好ましい。というのは、圧下率が15％未満の場合は圧延再結晶の機構が作用せず結晶組織の均一化が得られず、一方60％を超えると集合粗繊の集積化が起り第２回目の圧延の効果が得られなくなるからである。また、最終圧延の圧下率は80〜90％程度とすることが好ましい。というのは、圧下率が90％を超えた場合、２次再結晶が困難となり、一方80％未満では良好な２次再結晶粒の方位が得られず製品の磁束密度が低下するからである。
【００４２】
また、熱延板焼鈍および中間焼鈍において、焼鈍温度が過度に低い場合、圧延後の再結晶組織において２次再結晶の核となる（１１０）粒の頻度が不足し、良好な方位の２次再結晶組織が得られなくなる。（１１０）粒の強度を得るためには熱延板焼鈍後の結晶組織を一定サイズ以上に粗大化する必要があり、このためには 800℃以上の温度まで昇温することが不可欠である。一方、焼鈍温度の上限については微細に析出したMn（Se＋Ｓ) ，AlＮを再固溶あるいはオストワルド成長させないことが肝要なため、1200℃以下の焼鈍が好ましい。
なお、かような焼純の冷却過程については、とくに制限されることはないが、焼純後の鋼中の固溶Ｃを増加させる点から急冷処理を行ったり、鋼中の微細カーバイドを析出させるための急冷低温保持処理を行ったりすることは、製品の磁気特性を向上させる上で有効である。また、焼鈍の雰囲気の酸化性を高めて鋼板表層部を脱炭する公知の手段も有効な働きをする。
【００４３】
さらに、最終冷間圧延を、公知のように 100〜350 ℃での温間圧延としたり、または 100〜350 ℃で10〜60分間のパス間時効処理を付加することにより、１次再結晶の集合組織を一層改善することができる。
また、最終冷間圧延後、公知のように磁区細分化のため鋼板表面に線状の溝を設ける処理を行うことも可能である。
【００４４】
ついで、最終板厚とした鋼板は、公知の手法による脱炭・１次再結晶焼鈍を施したのち、MgＯを主成分とする焼純分離剤を鋼板表面に塗布してから最終仕上げ焼鈍に供されるが、その時Ti化合物を添加したり、CaやＢを焼鈍分離剤中に含有させることは磁気特性をさらに向上させる効果があり、好ましい。
【００４５】
最終仕上げ焼鈍において、昇温途中少なくとも1050℃以上、好ましくは 900℃以上の温度域については、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、Ｈ₂ 雰囲気は、最終仕上げ焼鈍中に形成される被膜中の酸化物や窒化物の形成に重要な作用を及ぼし、 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有効である。最終仕上げ焼鈍後は、未反応分離剤を除去したのち、鋼板表面に絶縁コーティングを塗布して製品とするが、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いし、また絶縁コーティングとして張力コーティングを用いてもよい。さらに、コーティングの塗布焼き付処理を平坦化処理と兼ねてもよい。
また、２次再結晶後の鋼板には鉄損低減効果を得るため、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へこみ領域を設けたりする処理を施すこともできる。
【００４６】
【実施例】
実施例１
Ｃ：0.08％, Si：3.50％, Mn：0.075 ％, Se：0.022 ％, Sb：0.045 ％, Al：0.027 ％, Ｎ：0.0088％, Bi：0.025 ％, Cr：0.20％, Cu：0.10％およびMo：0.022 ％を含有し、残部はFeおよび不可避的不純物の組成になる溶鋼を、連続鋳造によりスラブとした。このスラブを、ガス炉で加熱後、誘導加熱式（電気式）の炉で1400℃に加熱したのち、熱延により 2.0mm厚の熱延板とし、550 ℃でコイルに巻き取った。
この時のスラブ加熱条件および熱延条件を表４に示す。
ついで、この鋼板を1150℃まで昇温し、均熱時間が90秒間の熱延板焼鈍を施し、25℃/sの速度で急冷後、酸洗し、冷間圧延と 200℃の温間圧延を組み合わせて0.22mm厚に１回の圧延で仕上げた。
その後、脱脂処理を施したのち、 850℃で４分間の脱炭焼鈍を施した。
【００４７】
ついで、MgＯに SrSO₄を２％、TiO₂を５％添加した焼純分離剤を鋼板に10g/m²の塗布量で塗布し、最終仕上げ焼純として、 850℃までＮ₂ 中で30℃/hの速度で、また 850℃から1050℃まで（25vol%N₂＋75vol%H₂）の混合雰囲気中で12.5℃/hの速度で、その後はＨ₂ 中で25℃/hの速度で1200℃まで昇温し、1200℃で８時間保持した後、 600℃までＨ₂ 中で降温し 600℃からはAr雰囲気中で降温した。
上記の最終仕上げ焼純後、未反応の焼純分離剤を除去した後、50％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たのち、840 ℃で30秒間焼き付けて製品板とした。
かくして得られた製品板の磁気特性および被膜特性について調べた結果を、表５に示す。
【００４８】
【表４】

【００４９】
【表５】

【００５０】
表５に示したとおり、本発明に従って得られた電磁鋼板は、磁気特性および被膜特性が飛躍的に向上している。
【００５１】
実施例２
Ｃ：0.06％，Si：3.15％，Mn：0.075 ％，Ｓ：0.020 ％，Sn：0.025 ％，Al：0.025 ％，Ｎ：0.0095％，Bi：0.030 ％およびCu：0.10％を含有し、残部はFeおよび不可避的不純物の組成になる溶鋼を、連続鋳造によりスラブとした。このスラブを、表６に示す条件でスラブ加熱および熱間圧延を行って、2.2 mm厚の熱延板としたのち、570 ℃でコイルに巻き取った。スラブ加熱は、ガス加熱炉に引き続き電気式（誘導式）加熱炉で加熱を行った。
ついで、この鋼板を、1150℃まで昇温し、90秒間均熱したのち35℃/sの速度で 400℃まで急冷する熱延板焼純を施し、引き続き酸洗後、冷間圧延と 200℃の温間圧延を組み合わせて0.26mm厚に１回の圧延で仕上げた。
その後、脱脂処理を施したのち、850 ℃で３分間の脱炭焼純を施した。
【００５２】
、ついで、MgＯに MgSO₄：２％添加したものを焼純分離剤として鋼板に塗布し、最終仕上げ焼鈍として、850 ℃までＮ₂ 中で30℃/hの速度で、また 850℃から1050℃まで（25vol%N₂＋75vol%H₂）の混合雰囲気中で12.5℃/hの速度で、その後はＨ₂ 中で25℃/hの速度で1180℃まで昇温し、1180℃で４時間保持した後、 600℃までＨ₂ 中で降温し 600℃からはAr雰囲気中で降温した。
上記の最終仕上げ焼鈍後、未反応の焼純分離剤を除去した後、50％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たのち、840 ℃で30秒間焼き付けて製品板とした。
かくして得られた製品板の磁気特性および被膜特性について調べた結果を、表７に示す。
【００５３】
【表６】

【００５４】
【表７】

【００５５】
表７に示したとおり、本発明に従って得られた電磁鋼板は、磁気特性および被膜特性が飛躍的に向上している。
【００５６】
実施例３
表８に示す成分組成になる溶鋼を、連続鋳造によりスラブとした。このスラブを表９，10に示す条件でスラブ加熱および熱間圧延を行って、2.4 mm厚の熱延板とした。スラブ加熱は、ガス加熱炉に引き続き電気式（誘導式）加熱炉で加熱を行った（一部についてはガス炉のみ）。
ついで、この鋼板を、950 ℃まで昇温し、55秒間均熱したのち37℃/sの速度で急冷する熱延板焼鈍を施し、酸洗後、１回目の冷延で 1.8mm厚に仕上げた。ついで、1150℃まで昇温し90秒間の中間焼鈍を施し、30℃/sの速度で急冷した。その後、250 ℃の温間圧延で0.27mm厚に仕上げた。
その後、脱脂処理を施し、脱炭焼鈍を昇温速度：35℃/s、均熱温度：830 ℃、均熱時間：３分間、露点：59℃、水素濃度：50 vol％、窒素濃度：50 vol％の雰囲気中で行った後、アンモニアガス雰囲気での窒化処理によりＮ含有量を0.0180％まで富化した。
【００５７】
ついで、0.12％のCaと0.05％のＢを含有するMgＯに Sr(OH)₂を 3.5％、 TiO₂を10％、 SrSO₄を１％添加したものを焼純分離剤として鋼板に12g/m²塗布し、最終仕上げ焼鈍として、 900℃までＮ₂ 中で30℃/hの速度で、また 900℃から1050℃まで（25vol%N₂＋75vol%H₂）の混合雰囲気中で12.5℃/hの速度で、その後はＨ₂ 中で25℃/hの速度で1200℃まで昇温し、1200℃で８時間保持したのち、 600℃までＨ₂ 中で降温し 600℃からはＮ₂ 雰囲気中で降温した。
上記の最終仕上げ焼鈍後、未反応の焼純分離剤を除去した後、50％コロイダルシリカを含有するリン酸アルミニウムを張力コーティングとして塗布したのち、850 ℃で焼き付け、その後磁区細分化処理としてレーザーを 7.5mmピッチで照射し製品とした。
かくして得られた製品板の磁気特性および被膜特性について調べた結果を、表11に示す。
【００５８】
【表８】

【００５９】
【表９】

【００６０】
【表１０】

【００６１】
【表１１】

【００６２】
表11に示したとおり、本発明に従って得られた電磁鋼板は、磁気特性および被膜特性が飛躍的に向上している。
【００６３】
【発明の効果】
かくして、本発明によれば、極めて優れた鉄損特性を有し、かつ被膜欠陥がない高磁束密度方向性電磁鋼板を安定して得ることができる。
【図面の簡単な説明】
【図１】 加熱温度と酸素濃度が、鋼板表層のBi濃度、中心層のBi濃度および表層から５mm深い箇所のBi濃度に及ばす影響を示した図である。
【図２】 加熱温度と加熱時間が鋼板表層のBi濃度に及ぼす影響を示した図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a grain-oriented electrical steel sheet that is suitable for use in iron cores such as transformers and generators. In particular, the present invention intends to advantageously improve surface properties and magnetic properties.
[0002]
[Prior art]
The grain-oriented electrical steel sheet containing Si and having the crystal orientation of the product oriented in the {110} <001> orientation exhibits excellent soft magnetic properties and is widely used as various iron core materials in the commercial frequency range. Yes. The properties required for such an electrical steel sheet include the iron loss value W when magnetized to 1.7T at a frequency of 50 Hz._17/50 It is particularly important that (W / kg) is low.
[0003]
In general, to reduce the iron loss of electromagnetic materials, increase the electric resistance by increasing the Si content, which is effective in reducing eddy current loss, reduce the steel plate thickness, and reduce the crystal grain size of the product. There are known a method and a method for improving the magnetic flux density by increasing the degree of integration of crystal orientations.
Among these, the method for increasing the Si content has a limit to deteriorate the rollability and workability when Si is excessively contained. Further, the method for further reducing the steel plate thickness and the crystal grain size are reduced. This method is not preferable because the manufacturing cost is extremely increased.
[0004]
The method of improving the remaining magnetic flux density has been well studied so far, and the feature is limited to the selection of the type of precipitate called an inhibitor that governs secondary recrystallization and the accompanying morphology control technology. Is not an exaggeration.
Inhibitors are largely controlled mainly by uniform fine dispersion in the hot rolling process, but the actual condition is that the conditions in which the process control is always the first in other processes are selected.
[0005]
As typical inhibitors, MnS, MnSe, AlN and the like have been put to practical use so far. In particular, when AlN is used as the main inhibitor, it is possible to obtain a texture suitable for secondary recrystallization in the {110} <001> orientation by increasing the rolling reduction to 80% or more in the cold rolling process. The magnetic flux density is industrially realized.
Recently, for the purpose of further strengthening the inhibitor function, for example, Japanese Patent Publication No. 60-48886 discloses a method of adding Cu or Sn to steel, and Japanese Patent Application Laid-Open No. 2-115319 discloses Sb or Mo. Each of the methods for adding is proposed.
[0006]
Furthermore, Japanese Examined Patent Publication No. 62-45285 discloses a method in which the amount of S and Se in the material is reduced and nitriding is performed in the middle of the process. According to this method, since it is possible to omit the high-temperature heating of the slab, which is essential for the control of the inhibitor, there is an advantage that various defects associated with the conventional high-temperature heating can be fundamentally solved.
Therefore, according to this method, for example, as disclosed in Japanese Patent Publication No. 57-41526, the crystal structure of the slab is improved by using electromagnetic stirring in the stage of producing a continuously cast slab, and the high temperature of the next process is improved. A method for eliminating the secondary recrystallization failure caused by the grain growth of the slab by heating is not necessarily required.
[0007]
As described above, the magnetic properties of grain-oriented electrical steel sheets have been greatly improved. However, as global environmental protection has increased, there is an increasing demand for transformer manufacturers to improve their properties.
[0008]
By the way, as disclosed in Japanese Patent Application Laid-Open No. 51-41624, Bi is well known as an element that is extremely effective in enhancing the function of inhibitors.
However, although the effect of Bi as an element for enhancing the inhibitor function is excellent,
1) Secondary recrystallization is unstable and magnetic properties are not stable.
2) Production of forsterite film unique to grain-oriented electrical steel sheet is hindered
There was a defect.
In this regard, JP-A-8-232019 discloses a method for improving the coating film, which comprises controlling the amount of oxygen after decarburizing and purifying and adding a specific compound or the like in the annealing separator, There are many unsolved parts in this method, and the actual situation is that it has not yet been implemented industrially.
[0009]
[Problems to be solved by the invention]
The present invention has been developed in view of the above-mentioned present situation, and eliminates the instability of secondary recrystallization when producing a grain oriented electrical steel sheet containing Bi together with known inhibitors, particularly Al and N. , Extremely high magnetic flux density B₈ Advantageous production of high magnetic flux density grain-oriented electrical steel sheets with extremely few surface defects and excellent magnetic properties, which can effectively eliminate defects inherent in Bi-containing steels. The purpose is to propose a method.
[0010]
[Means for Solving the Problems]
  In order to achieve the above object, the inventors have intensively studied the influence on the secondary recrystallization of Bi and the film formation. As a result, the temperature history in the hot rolling process is affected by the film characteristics and the magnetic characteristics. The present invention is extremely important and the present inventionTheIt came to be completed.
[0012]
  That is, the gist configuration of the present invention is as follows.
1. Si: 2.5 to 4.5 mass%, including one or two selected from C and Ni in the range of 0.03 ≦ C + (Ni / 30) ≦ 0.10 mass%, and Bi: 0.005 to 0.05 mass% and Mn : 0.05 to 1.5 mass%, and further, as inhibitor elements, S and / or Se: 0.010 to 0.040 mass%, sol.Al: 0.015 to 0.050 mass% and N: 0.005 to 0.015 mass%,The rest Fe And inevitable impuritiesAfter heating the steel slab to the composition to 1350 ° C or higher, it is used as a hot-rolled sheet, and if necessary, hot-rolled sheet annealing is performed. After pickling, it is cold-rolled once or twice, including intermediate sinter. After finishing to the final thickness, decarburization annealing that also serves as primary recrystallization is applied, and then a sinter separation agent mainly composed of MgO is applied, followed by secondary recrystallization annealing and purification annealing. In the manufacturing method of grain-oriented electrical steel sheet consisting of a series of steps to perform final finish annealing,
  During hot rolling, before starting rough rolling, heat treatment is performed at a temperature of 1125 ° C or higher for 1 hour or more and 10 hours or less in an atmosphere having an average oxygen concentration of 100 to 50000 ppm, and finish rolling from the start of rough rolling. A method for producing a grain-oriented electrical steel sheet, characterized in that the time until completion is 30 seconds or more and 300 seconds or less, and the surface temperature of the rolled material is always kept lower than the plate thickness center temperature during the rolling.
[0013]
2. Si: 2.5-4.5 mass%, including one or two selected from C and Ni in the range of 0.03 ≦ C + (Ni / 30) ≦ 0.10 mass%, and Bi: 0.005-0.05 mass% and Mn : 0.05 to 1.5 mass%, and as an inhibitor element, S and / or Se: 0.010 mass%Less than, Sol.Al: 0.015 to 0.050 mass% and N: 0.005 to 0.015 mass%,The rest Fe And inevitable impuritiesThe steel slab having the composition is heated to 1250 ° C or lower, then hot-rolled, and if necessary, hot-rolled sheet is annealed, pickled, and then cold-rolled once or twice including intermediate sinter. After finishing to the final thickness, decarburization annealing that also serves as primary recrystallization is applied, and then a sinter separation agent mainly composed of MgO is applied, followed by secondary recrystallization annealing and purification annealing. In the method for producing a grain-oriented electrical steel sheet comprising a series of steps of performing final finishing annealing and nitriding in any step before the start of secondary recrystallization after the end of hot rolling,
  During hot rolling, before starting rough rolling, heat treatment is performed for 1 hour to 10 hours at a temperature of 1125 ° C or higher in an atmosphere with an average oxygen concentration of 100 to 50000 ppm. A method for producing a grain-oriented electrical steel sheet, characterized in that the time until completion is 30 seconds or more and 300 seconds or less, and the surface temperature of the rolled material is always kept lower than the plate thickness center temperature during the rolling.
[0014]
3. In the above 1 or 2, as an inhibitor reinforcing element, further in the steel slab, Cu : 0.05 ~ 0.5mass %, Sn : 0.05 ~ 0.5mass %, Sb : 0.005 ~ 0.10mass %, As : 0.005 ~ 0.10mass %, Mo : 0.005 ~ 0.10mass %, Te : 0.005 ~ 0.10mass %, P: 0.005 ~ 0.10mass % And B: 0.001 ~ 0.01mass A method for producing a grain-oriented electrical steel sheet, comprising one or more selected from%.
4. Above 1Any of ~ 3In order to produce a good forsterite film, the steel slab is further characterized by containing Cr: 0.05 to 0.50 mass%.WhoA method for producing a grain-oriented electrical steel sheet.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the experimental results on which the present invention is based will be described.
First, the following experiment was conducted to clarify the effect of hot rolling conditions on the magnetic properties of Bi-added steel. In the following, “%” used for displaying the content of each element represents a mass percentage (mass%) unless otherwise specified.
A continuous cast slab having a composition containing C: 0.06%, Si: 3.33%, Mn: 0.06%, Se: 0.024%, Al: 0.028%, N: 0.0090%, Bi: 0.025% and Cu: 0.08%, A hot-rolled sheet having a thickness of 2.7 mm was obtained under various slab heating conditions and hot-rolling conditions shown in Table 1. In the slab heating, after heating in a gas heating furnace, heating was continued in an electric (induction) heating furnace.
Next, hot-rolled sheet annealing was performed at 950 ° C for 1 minute, followed by rapid cooling treatment, pickling, then cold rolling to an intermediate thickness of 1.8 mm, 1120 ° C, intermediate annealing for 120 seconds and 35 ° C After a rapid cooling process at a cooling rate of / s, it was finished into a cold rolled sheet having a final sheet thickness of 0.22 mm by cold rolling (rolling roll diameter: 70 mm) including warm rolling at 200 ° C.
Then, after decarburization annealing at 840 ° C for 2 minutes, the surface layer is made of SiO at 860 ° C.₂After reduction to 6g / m per side of the sinter separating agent mainly composed of MgO²After application, the temperature was increased to 850 ° C at a rate of 8 ° C / h in a nitrogen atmosphere, and then 1200 ° C at a rate of 10 ° C / h in an atmosphere of nitrogen: 25 vol% and hydrogen: 75 vol%. Heat to ℃ and H for 5 hours at 1200 ℃₂Purification annealing was performed.
[0016]
Table 2 shows the results of examining the magnetic properties and film properties of the grain-oriented electrical steel sheet thus obtained.
The magnetic characteristics are as follows: magnetic flux density B when magnetized at 800 A / m₈(T) and magnetic flux density: 1.7 T, frequency: iron loss W at 50 Hz_17/50(W / kg). Further, the film characteristics were evaluated by the bending peeling characteristics determined by the peeling limit diameter of the film when the product plate was wound around a round bar.
[0017]
[Table 1]

[0018]
[Table 2]

[0019]
As shown in Table 2, in Bi-added steel, the atmosphere during slab heating, the time during hot rolling, and the hot-rolled sheet rather than the finish entry temperature and coil winding temperature that have been conventionally controlled It has been found that good film characteristics and magnetic characteristics can be obtained when items that have not been controlled so far, such as the temperature difference between the surface and the center, are combined under certain conditions.
[0020]
  In the above experiment, the reason why the film characteristics are good is considered that the surface was modified in the hot rolling process.
  Therefore, in order to clarify the effects of the heating temperature and the oxygen concentration of the atmosphere on the slab surface during slab heating, the following experiment was conducted.
  As test steel components, C: 0.05%, Si: 3.15%, Mn: 0.055%, Bi: 0.015%, Al: 0.022%, N: 0.0075% and S: 0.020%And the rest Fe And inevitable impuritiesThe steel having the composition was made into a slab by continuous casting, and then a sample of 100 mm × 100 mm × 100 mm was cut out.
  This sample was placed in a soaking furnace for 3 hours with various changes in oxygen concentration and heating temperature in the heating atmosphere.
  Then, the result of having measured the Bi amount of the surface iron surface layer using fluorescent X-rays is shown in FIG. 1 in relation to the oxygen concentration in the heating atmosphere.
[0021]
As shown in the figure, when the average oxygen concentration in the heating atmosphere is 100 ppm or higher and the heating temperature is 1125 ° C or higher, the amount of Bi on the surface of the railway is higher than that of the base metal. It became clear that it was reduced to 1/2 or less.
It was also found that when the average oxygen concentration in the heating atmosphere exceeds 50000 ppm, the Bi concentration is reduced to 1/2 or less of that at the center even at a location 5 mm deep from the surface.
[0022]
Next, in order to clarify the relationship between the heating temperature and the heating time during slab heating, the oxygen concentration in the atmosphere is kept constant at 2000 ppm, and Bi of the surface layer of the steel sheet when the heating temperature and the heating time are variously changed. The amount was investigated.
The obtained results are shown in FIG.
As shown in the figure, it was found that the Bi concentration on the surface was reduced to 1/2 or less of that at the center by heating at a temperature of 1125 ° C. or higher for 1 hour or longer.
[0023]
The reason why the film properties and magnetic properties are improved by the slab heat treatment as described above is considered as follows.
That is, since Bi has a very small amount of solid solution in iron, when steel is made into a slab by continuous casting, it is very uniformly dispersed, and Bi exists in the slab surface layer at the same concentration as the central portion of the plate thickness. For this reason, Bi existing in the surface layer during secondary recrystallization annealing inhibits the formation of forsterite, causing significant coating defects, and the coating phase defects cause excessive action in the steel due to coating defects, The decomposition behavior of the inhibitor varies greatly and normal secondary recrystallization does not occur. In addition, since secondary recrystallization annealing is usually performed in a coil shape, the manner of contact with the gas phase atmosphere differs in the width direction and longitudinal direction of the steel sheet, and the manner of film formation and secondary recrystallization varies depending on the location. Therefore, it becomes extremely difficult to make a uniform product.
[0024]
Therefore, it is considered that the Bi concentration in the surface layer needs to be reduced within a range that does not affect the inhibitor strength.
That is, as shown in FIGS. 1 and 2, the slab heating is carried out in an atmosphere having an average oxygen concentration of 100 to 50000 ppm at a heating temperature of 1125 ° C. or more for 1 hour or more, so that Bi existing on the surface is present. It is important to remove with the scale. In this case, holding at a higher temperature than necessary is not preferable because not only the surface layer but also the internal Bi concentration is lowered.
[0025]
Further, when reducing the plate thickness by hot rolling, it is considered important to keep the temperature of the surface layer lower than the center at all times in order to prevent excessive Bi dissipation from the surface layer.
That is, during hot rolling, a large amount of dislocations are introduced into the steel by rolling, so the diffusion coefficient becomes very high, but if the temperature of the surface layer is lowered, the diffusion rate at the surface becomes the central layer. It is considered that the diffusion of Bi from the central layer can be suppressed as a result.
[0026]
Furthermore, by limiting the time required for the hot rolling time to a predetermined range, the Bi concentration can be appropriately controlled, thereby ensuring a Bi concentration of a certain concentration or more at the center of the plate thickness, It becomes possible to secure the necessary inhibitory force during the next recrystallization.
Thus, it is considered that the instability of secondary recrystallization due to the conventional addition of Bi has been eliminated, and it has become possible to improve both the film characteristics and stabilize the magnetic characteristics.
[0027]
Next, as a result of intensive studies on how to improve the forsterite film formation of the Bi additive material, the inventors have found that the addition of Cr into the steel is extremely effective.
Hereinafter, this finding will be described based on the experimental results of the combined addition with Bi while changing the Cr addition amount.
C: 0.05%, Ni: 0.10%, Si: 3.30%, Mn: 0.06%, Se: 0.014%, Sb: 0.045%, Bi: 0.025%, Al: 0.027%, N: 0.0095%, Cu: 0.09% and Slabs were prepared based on Sn: 0.1% and Cr containing 0.03, 0.05, 0.15, 0.2, 0.5, 0.7%, respectively.
The slab was heated in an atmosphere of oxygen concentration: 500 ppm at 1200 ° C. for 2 hours, and then heated in an electric heating furnace at 1400 ° C. for 1 hour in an atmosphere of oxygen concentration: 1500 ppm. After that, the first pass of rough rolling is surface temperature: 1350 ° C, center temperature: 1360 ° C, reduction rate: 50%, and the second pass is surface temperature: 1300 ° C, center temperature: 1320 ° C, reduction rate: 35%, After performing the third pass at a surface temperature of 1250 ° C and a center temperature of 1290 ° C, finish rolling is performed. The surface temperature of the entrance side is 1100 ° C, the center temperature is 1120 ° C, and the surface temperature of the exit side is 990 ° C. A temperature of 995 ° C. was used to obtain a hot-rolled sheet having a thickness of 2.2 mm, and the coil was wound around a coil at a winding temperature of 575 ° C.
[0028]
Then, after soaking at 950 ° C. for 2 minutes, hot-rolled sheet annealing was performed at an average rate of 25 ° C./s up to 300 ° C., then pickling and cold rolling to 1.5 mm. Subsequently, after intermediate annealing at 1070 ° C. for 1 minute, the sheet thickness was reduced to 0.22 mm by cold rolling including warm rolling at 250 ° C., and then decarburized and purified at 840 ° C. for 2 minutes.
Then, after applying a pure separation agent composed mainly of MgO, the temperature was raised to 850 ° C at 10 ° C / h in a nitrogen atmosphere, and after 15 hours of holding annealing, nitrogen: 25 vol% and hydrogen : Finish annealing was performed in a 75 vol% atmosphere up to 1200 ° C at a heating rate of 30 ° C / h.
Table 3 shows the results of examining the magnetic properties and coating properties of the product plates thus obtained.
The coating properties were evaluated by the peeling limit diameter of the coating by a bending test in which magnesium phosphate containing 40% colloidal silica was applied as a coating agent, baked at 850 ° C., and wound around a round bar.
[0029]
[Table 3]

[0030]
As is apparent from Table 3, by adding 0.05% or more of Cr, in addition to the treatment for reducing the surface layer Bi in hot rolling, a further film improvement effect was recognized.
Generation of such a good film makes the interaction with the gas phase atmosphere during secondary recrystallization appropriate, and the effect of improving the magnetic properties is also achieved. In addition, forsterite imparts tension to the steel sheet, greatly contributing to the improvement of iron loss.
The effect of Cr is not always clear, but the Cr-added material changes the subscale structure of the decarburized annealed plate, effectively promoting the reaction with MgO during secondary recrystallization annealing. it is conceivable that.
However, excessive addition of Cr causes a decrease in magnetic flux density.
[0031]
Next, suitable manufacturing conditions for the grain-oriented electrical steel sheet according to the present invention will be described.
First, material components will be described.
Si: 2.5-4.5%
Si is an indispensable element for increasing electrical resistance and reducing iron loss. For this purpose, it is necessary to contain 2.5% or more, but if it exceeds 4.5%, the workability deteriorates and the manufacturing itself Since the processing of the product becomes extremely difficult, the Si content is limited to the range of 2.5 to 4.5%.
[0032]
0.03 ≦ C + (Ni / 30) ≦ 0.10%
It is a feature of the present invention that the content of C and Ni is 0.10% or less in the formula of (C + Ni / 30).
This is because when (C + Ni / 30) exceeds 0.10%, the amount of γ transformation becomes excessive, and the uniformity of the distribution of inhibitors such as MnSe and MnS precipitated during hot rolling is inhibited. In addition, there is a disadvantage that the decarburization annealing load is increased and a decarburization failure is likely to occur. On the other hand, if (C + Ni / 30) is less than 0.03%, the effect of improving the structure cannot be obtained, the secondary recrystallization becomes incomplete, and the magnetic characteristics are also deteriorated. Therefore, C and Ni are limited to the range of 0.03 to 0.10% in the formula (C + Ni / 30) in either case of single or composite inclusion.
[0033]
Bi: 0.005 to 0.05%
The addition of Bi is one of the features of the present invention. If the amount of Bi is less than 0.005%, the expected effect as described above cannot be obtained. On the other hand, if it exceeds 0.05%, uniform dispersion becomes difficult. Therefore, Bi should be contained in the range of 0.005 to 0.05%. did.
This Bi strongly suppresses the oxidation reaction and is formed on the decarburized and annealed plate.₂Therefore, it is an element that is expected to make it difficult to form a film by extending the prior art.
[0034]
Mn: 0.05-1.5%
Mn, like Si, is a useful element not only for increasing electrical resistance and reducing iron loss, but also for improving hot workability during production. For this purpose, a content of 0.05% or more is necessary. However, if the content exceeds 1.5%, the γ transformation is induced and the magnetic properties deteriorate, so the Mn content is in the range of 0.05 to 1.5%. Limited.
[0035]
  The inhibitor elements are as follows.
S, Se: 0.010 to 0.040% or 0.010%Less than
  As an inhibitor component, Se and S can be contained alone or in combination. These components precipitate as Mn compounds or Cu compounds in the steel, but in order to maintain the suppression effect, they must be contained in a total amount of 0.010% or more. However, if they exceed 0.040%, they are completely solidified even at high temperature slab heating. Since it cannot be dissolved and becomes a coarse precipitate, which is rather harmful, it is limited to the range of 0.010 to 0.040%.
  On the other hand, when the high temperature slab heating is omitted, the smaller the Se and S, the lower the solid solution temperature. Therefore, in that case, both should be less than 0.010%.
[0036]
sol.Al: 0.015-0.050% and N: 0.005-0.015%
When the final cold rolling reduction is 80% or more, the secondary recrystallization temperature becomes very high, so it is necessary to contain an inhibitor component that is stable at high temperatures in addition to these elements in the steel. As the component, Al and N are preferable.
Among these, it is necessary to contain Al as 0.015-0.050% as sol.Al (acid-soluble Al). This is because when the amount of sol.Al is less than 0.015%, the amount of precipitated AlN is insufficient and good secondary recrystallization cannot be obtained, while when it exceeds 0.050%, the size to function as an inhibitor is reduced. This is because uniform dispersion becomes difficult.
N needs to be contained in an amount of 0.005% or more, but if it exceeds 0.015%, it will gasify in steel and cause defects such as blisters, so N should be contained in the range of 0.005 to 0.015%. To do.
[0037]
  The inhibitor reinforcing elements are as follows.
  Cu, Sn, Sb, Mo, As, Te, P, B and the like have an auxiliary function of enhancing the inhibitory power of known inhibitors, and thus are preferably added to the steel as needed. For the preferable addition amount necessary for this, Cu and Sn are 0.05 to 0.5%, Sb, As, Mo, Te and P are 0.005 to 0.10%, and B is 0.0010 to 0.01%.
  As for other additive elements, for example, Ge, Co and the like are preferably contained as appropriate because they have the effect of improving the surface properties of the steel sheet.
[0038]
Cr: 0.05-0.50%
As described above, Bi strongly suppresses the oxidation reaction and is formed on the decarburized and annealed plate.₂Therefore, it is an element that is difficult to produce a film by the conventional technique.
However, the above problem can be solved by adding an appropriate amount of Cr.
This time, by adding Cr, it became possible to produce a coating because Cr canceled the oxidation inhibition effect of Bi and decarburized and annealed sheet SiO₂This is probably because it has the effect of improving the morphology well, promotes the forsterite formation reaction, or has both effects. Here, if the content is less than 0.05%, the effect of addition is poor. On the other hand, if it exceeds 0.50%, the effect of improving the film is saturated, the cost is increased, and the magnetic flux density tends to decrease. Limited to a range of ~ 0.50%.
[0039]
Next, the manufacturing conditions according to the present invention will be specifically described.
The molten steel adjusted to the above-mentioned preferred component composition is usually made into a slab by a continuous casting method or an ingot-bundling method.
Then, this slab is usually subjected to slab heating and then hot rolled to form a hot rolled coil. At this time, it is important that the slab heating temperature is 1350 ° C. or higher. This is because if the slab heating temperature is less than 1350 ° C., the inhibitor is not sufficiently dissolved, and a fine and uniform dispersed precipitation state such as Mn (Se + S), AlN cannot be obtained.
On the other hand, in the method of limiting the composition that requires a high temperature for solution treatment, such as Se and S, and omitting the high-temperature slab heating, the slab heating temperature should be 1250 ° C. or less at which grain growth does not occur. It is effective in homogenizing the spread fiber and improving the magnetic properties.
In the hot rolling, it is effective to add known techniques such as thickness reduction processing and width reduction processing for homogenizing the structure before and after slab heating as needed.
[0040]
The hot rolling, which is a feature of the present invention, is that slab heating is performed in an atmosphere having an average oxygen concentration of 100 to 50000 ppm at a temperature of 1125 ° C. or more for 1 hour or more, so that Bi existing on the surface is scaled into the heating furnace. It is to peel and remove.
At this time, holding at a high temperature for 10 hours or more is not preferable because the Bi concentration is reduced not only to the surface layer but also to the inside.
Further, when the plate thickness is reduced by hot rolling, it is necessary to keep the temperature of the surface layer always lower than the center in order to prevent excessive Bi from escaping from the surface layer. In addition, during hot rolling, a large amount of dislocations are introduced into the steel by rolling, and the diffusion coefficient is very high. Even in this aspect, the temperature of the surface layer is lowered and the diffusion rate on the surface is the center. If it is made slower than the layer, the diffusion of Bi from the central layer can be suppressed.
Furthermore, by limiting the time required for the hot rolling time to 30 to 300 seconds, the Bi concentration can be appropriately controlled, and thereby a Bi concentration of a certain concentration or more can be secured at the center of the plate thickness. Therefore, it becomes possible to ensure the suppressing force required at the time of secondary recrystallization.
Thus, the instability of secondary recrystallization, which has been a concern in the past when adding Bi, is eliminated, and the magnetic properties can be stabilized.
[0041]
About the cold rolling process, after the hot-rolled sheet annealing, the cold-rolled one-time method in which the final sheet thickness is obtained by one cold rolling, or hot-rolled sheet annealing as necessary, and two times sandwiching the intermediate annealing The cold rolling twice method which performs the above cold rolling is employable.
About the rolling reduction of cold rolling, as is conventionally known, the first rolling of the cold rolling two-time method is preferably about 15 to 60%. This is because when the rolling reduction is less than 15%, the rolling recrystallization mechanism does not work and the crystal structure is not uniformed. On the other hand, when it exceeds 60%, the aggregate coarse fibers are accumulated and the second time. This is because the rolling effect cannot be obtained. Further, the rolling reduction of the final rolling is preferably about 80 to 90%. This is because when the rolling reduction exceeds 90%, secondary recrystallization becomes difficult, whereas when the rolling reduction is less than 80%, good secondary recrystallization grain orientation cannot be obtained and the magnetic flux density of the product decreases. .
[0042]
In addition, in the hot-rolled sheet annealing and the intermediate annealing, when the annealing temperature is excessively low, the frequency of (110) grains serving as the nucleus of secondary recrystallization in the recrystallized structure after rolling is insufficient, and a secondary having good orientation A recrystallized structure cannot be obtained. In order to obtain the strength of (110) grains, it is necessary to coarsen the crystal structure after hot-rolled sheet annealing to a certain size or more. For this purpose, it is essential to raise the temperature to a temperature of 800 ° C. or higher. On the other hand, with respect to the upper limit of the annealing temperature, it is important not to re-dissolve finely precipitated Mn (Se + S) 2, AlN or to cause Ostwald growth, so annealing at 1200 ° C. or lower is preferable.
In addition, the cooling process of such smelting is not particularly limited, but rapid cooling treatment is performed from the point of increasing the solute C in the steel after squeezing, or fine carbide in the steel is precipitated. In order to improve the magnetic properties of the product, it is effective to perform a quenching and low-temperature holding treatment for the purpose. Also, known means for enhancing the oxidizability of the annealing atmosphere and decarburizing the steel sheet surface layer part also works effectively.
[0043]
Further, the final cold rolling may be performed by warm rolling at 100 to 350 ° C. as known, or by adding an aging treatment between passes at 100 to 350 ° C. for 10 to 60 minutes. The texture can be further improved.
In addition, after the final cold rolling, it is also possible to perform a process of providing a linear groove on the steel sheet surface for magnetic domain subdivision as is well known.
[0044]
Next, the steel sheet with the final thickness is subjected to decarburization and primary recrystallization annealing by a known method, and then applied to the steel sheet surface with a pure separation agent mainly composed of MgO, and then subjected to final finish annealing. However, at that time, it is preferable to add a Ti compound or to contain Ca or B in the annealing separator because it has the effect of further improving the magnetic properties.
[0045]
In the final finish annealing, at least 1050 ° C or higher, preferably 900 ° C or higher during the temperature rise,₂ It is necessary to raise the temperature in an atmosphere containing. That is, H₂ The atmosphere has an important effect on the formation of oxides and nitrides in the film formed during the final finish annealing, and it is effective to increase the reducibility especially in the middle to late stages of annealing at 900 ° C or higher. . After the final finish annealing, after removing the unreacted separation agent, an insulating coating is applied to the surface of the steel sheet to make a product. However, if necessary, the surface of the steel sheet may be mirrored before applying the coating. A tension coating may be used. Further, the coating baking process may be combined with the flattening process.
In addition, in order to obtain the iron loss reduction effect on the steel sheet after the secondary recrystallization, a known magnetic domain refinement process, that is, a plasma jet or laser irradiation is applied to the linear region, or a linear dent region is provided by a protruding roll. Can also be applied.
[0046]
【Example】
Example 1
C: 0.08%, Si: 3.50%, Mn: 0.075%, Se: 0.022%, Sb: 0.045%, Al: 0.027%, N: 0.0088%, Bi: 0.025%, Cr: 0.20%, Cu: 0.10% and Mol: Molten steel containing 0.022% and the balance of Fe and inevitable impurities was used as a slab by continuous casting. The slab was heated in a gas furnace and then heated to 1400 ° C. in an induction heating (electric) furnace, and then hot-rolled with a thickness of 2.0 mm by hot rolling and wound around a coil at 550 ° C.
Table 4 shows the slab heating conditions and hot rolling conditions at this time.
The steel sheet was then heated to 1150 ° C, subjected to hot-rolled sheet annealing for 90 seconds, quenched at a rate of 25 ° C / s, pickled, cold rolled and warm rolled at 200 ° C. And finished with a single rolling to a thickness of 0.22 mm.
Then, after degreasing, decarburization annealing was performed at 850 ° C. for 4 minutes.
[0047]
Then, SrSO to MgO_Four2%, TiO₂10g / m of tempered separating agent with 5% added to steel plate²As the final finish tempered, N up to 850 ℃₂ At a rate of 30 ℃ / h, and from 850 ℃ to 1050 ℃ (25vol% N₂+ 75vol% H₂) In a mixed atmosphere at a rate of 12.5 ° C / h, then H₂ The temperature was raised to 1200 ° C at a rate of 25 ° C / h, held at 1200 ° C for 8 hours, then H to 600 ° C.₂ The temperature was lowered and the temperature was lowered from 600 ° C. in an Ar atmosphere.
After the above final finish tempering, unreacted tempering separation agent was removed, magnesium phosphate containing 50% colloidal silica was applied as a tension coating, and baked at 840 ° C. for 30 seconds to obtain a product plate.
Table 5 shows the results of examining the magnetic properties and coating properties of the product plate thus obtained.
[0048]
[Table 4]

[0049]
[Table 5]

[0050]
As shown in Table 5, the magnetic steel sheet obtained according to the present invention has dramatically improved magnetic properties and coating properties.
[0051]
Example 2
Contains C: 0.06%, Si: 3.15%, Mn: 0.075%, S: 0.020%, Sn: 0.025%, Al: 0.025%, N: 0.0095%, Bi: 0.030% and Cu: 0.10%, the balance being The molten steel having a composition of Fe and inevitable impurities was made into a slab by continuous casting. This slab was slab-heated and hot-rolled under the conditions shown in Table 6 to obtain a hot-rolled sheet having a thickness of 2.2 mm, and then wound around a coil at 570 ° C. Slab heating was performed in an electric (induction) heating furnace following the gas heating furnace.
Next, the steel sheet was heated to 1150 ° C, soaked for 90 seconds, and then subjected to hot-rolled sheet tempering to rapidly cool to 400 ° C at a rate of 35 ° C / s, followed by pickling, cold rolling and 200 ° C. In combination with the warm rolling, it was finished in one rolling to 0.26 mm thickness.
Thereafter, after degreasing treatment, decarburized and pure for 3 minutes at 850 ° C.
[0052]
, Then MgO to MgSO_Four: 2% added as a pure separating agent is applied to steel plate, and as final finish annealing, N up to 850 ° C₂ At a rate of 30 ℃ / h, and from 850 ℃ to 1050 ℃ (25vol% N₂+ 75vol% H₂) In a mixed atmosphere at a rate of 12.5 ° C / h, then H₂ The temperature was raised to 1180 ° C at a rate of 25 ° C / h in the chamber, held at 1180 ° C for 4 hours, and then H to 600 ° C.₂ The temperature was lowered and the temperature was lowered from 600 ° C. in an Ar atmosphere.
After the above-described final finish annealing, unreacted sinter separation agent was removed, and then magnesium phosphate containing 50% colloidal silica was applied as a tension coating, and then baked at 840 ° C. for 30 seconds to obtain a product plate.
Table 7 shows the results of examining the magnetic properties and coating properties of the product plate thus obtained.
[0053]
[Table 6]

[0054]
[Table 7]

[0055]
As shown in Table 7, the magnetic steel sheet obtained according to the present invention has dramatically improved magnetic properties and coating properties.
[0056]
Example 3
The molten steel having the composition shown in Table 8 was made into a slab by continuous casting. This slab was subjected to slab heating and hot rolling under the conditions shown in Tables 9 and 10 to obtain a hot-rolled sheet having a thickness of 2.4 mm. Slab heating was performed in an electric (induction) heating furnace following the gas heating furnace (for some gas furnaces only).
Next, this steel sheet was heated to 950 ° C, soaked for 55 seconds, and then subjected to hot-rolled sheet annealing that was rapidly cooled at a rate of 37 ° C / s. It was. Next, the temperature was raised to 1150 ° C., intermediate annealing was performed for 90 seconds, and the mixture was rapidly cooled at a rate of 30 ° C./s. Thereafter, it was finished to a thickness of 0.27 mm by warm rolling at 250 ° C.
Then, degreasing is performed, and decarburization annealing is performed at a rate of temperature increase of 35 ° C / s, soaking temperature: 830 ° C, soaking time: 3 minutes, dew point: 59 ° C, hydrogen concentration: 50 vol%, nitrogen concentration: 50 After performing in a vol% atmosphere, the N content was enriched to 0.0180% by nitriding in an ammonia gas atmosphere.
[0057]
Next, Sr (OH) was added to MgO containing 0.12% Ca and 0.05% B.₂3.5%, TiO₂10%, SrSO_Four12g / m on steel sheet with 1% added as tempered separation agent²Apply and final finish annealing, up to 900 ℃ N₂ At a rate of 30 ℃ / h, and from 900 ℃ to 1050 ℃ (25vol% N₂+ 75vol% H₂) In a mixed atmosphere at a rate of 12.5 ° C / h, then H₂ The temperature was raised to 1200 ° C at a rate of 25 ° C / h, held at 1200 ° C for 8 hours, then H to 600 ° C₂ The temperature is lowered and the temperature is N from 600 ℃₂ The temperature was lowered in the atmosphere.
After the above final finish annealing, the unreacted sinter separation agent is removed, and then aluminum phosphate containing 50% colloidal silica is applied as a tension coating, and then baked at 850 ° C. Irradiated at a pitch of 7.5 mm to obtain a product.
Table 11 shows the results of examining the magnetic properties and coating properties of the product plates thus obtained.
[0058]
[Table 8]

[0059]
[Table 9]

[0060]
[Table 10]

[0061]
[Table 11]

[0062]
As shown in Table 11, the magnetic steel sheet obtained according to the present invention has dramatically improved magnetic properties and coating properties.
[0063]
【The invention's effect】
Thus, according to the present invention, a high magnetic flux density grain-oriented electrical steel sheet having extremely excellent iron loss characteristics and no coating defects can be stably obtained.
[Brief description of the drawings]
FIG. 1 is a diagram showing the influence of heating temperature and oxygen concentration on the Bi concentration of a steel sheet surface layer, the Bi concentration of a central layer, and the Bi concentration at a location 5 mm deep from the surface layer.
FIG. 2 is a graph showing the influence of heating temperature and heating time on the Bi concentration of the steel sheet surface layer.

Claims (4)

Si: 2.5 to 4.5 mass%, including one or two selected from C and Ni in the range of 0.03 ≦ C + (Ni / 30) ≦ 0.10 mass%, and Bi: 0.005 to 0.05 mass% and Mn : 0.05 to 1.5 mass%, further containing S and / or Se: 0.010 to 0.040 mass%, sol.Al: 0.015 to 0.050 mass% and N: 0.005 to 0.015 mass% as the inhibitor element, the balance being A steel slab with a composition of Fe and unavoidable impurities is heated to 1350 ° C or higher to be a hot-rolled sheet, subjected to hot-rolled sheet annealing as necessary, pickled, and once or twice including intermediate sinter After the above cold rolling and finishing to the final thickness, decarburization annealing that also serves as primary recrystallization is applied, and then a sinter separation agent mainly composed of MgO is applied, followed by secondary recrystallization. In the method for producing a grain-oriented electrical steel sheet comprising a series of steps of performing final finishing annealing consisting of annealing and purification annealing,
During hot rolling, before starting rough rolling, heat treatment is performed at a temperature of 1125 ° C or higher for 1 hour or more and 10 hours or less in an atmosphere having an average oxygen concentration of 100 to 50000 ppm, and finish rolling from the start of rough rolling. A method for producing a grain-oriented electrical steel sheet, characterized in that the time until completion is 30 seconds or more and 300 seconds or less, and the surface temperature of the rolled material is always kept lower than the plate thickness center temperature during the rolling. Si: 2.5 to 4.5 mass%, including one or two selected from C and Ni in the range of 0.03 ≦ C + (Ni / 30) ≦ 0.10 mass%, and Bi: 0.005 to 0.05 mass% and Mn : 0.05 to 1.5 mass%, further containing S and / or Se: less than 0.010 mass%, sol.Al: 0.015 to 0.050 mass% and N: 0.005 to 0.015 mass%, with the balance being Fe Steel slabs with inevitable impurity composition are heated to 1250 ° C or lower, then hot-rolled sheets, and if necessary, hot-rolled sheet annealing is performed, and after pickling, one or more times including intermediate sinter After finishing to the final plate thickness by cold rolling, decarburization annealing that also serves as primary recrystallization is applied, followed by application of a pure separating agent mainly composed of MgO, and then secondary recrystallization annealing. And final finishing annealing consisting of purification annealing, and nitriding treatment in any process after the end of hot rolling and before the start of secondary recrystallization The method of manufacturing a grain-oriented electrical steel sheet comprising a series of steps of performing,
During hot rolling, before starting rough rolling, heat treatment is performed for 1 hour to 10 hours at a temperature of 1125 ° C or higher in an atmosphere with an average oxygen concentration of 100 to 50000 ppm. A method for producing a grain-oriented electrical steel sheet, characterized in that the time until completion is 30 seconds or more and 300 seconds or less, and the surface temperature of the rolled material is always kept lower than the plate thickness center temperature during the rolling. In claim 1 or 2, as an inhibitor reinforcing element, further in the steel slab, Cu : 0.05 ~ 0.5mass %, Sn : 0.05 ~ 0.5mass %, Sb : 0.005 ~ 0.10mass %, As : 0.005 ~ 0.10mass %, Mo : 0.005 ~ 0.10mass %, Te : 0.005 ~ 0.10mass %, P: 0.005 ~ 0.10mass % And B: 0.001 ~ 0.01mass A method for producing grain-oriented electrical steel sheets, comprising one or more selected from%. The method for producing a grain-oriented electrical steel sheet according to any one of claims 1 to 3 , further comprising Cr: 0.05 to 0.50 mass% in the steel slab in order to produce a good forsterite film.

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