JP2005023393A - Production method of grain-oriented magnetic steel sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-cost production method of a grain-oriented magnetic steel sheet without using any inhibitor or applying any annealing separator, by establishing a production technique which avoids adhesion between steel sheets at finish annealing, even without applying the annealing separator. <P>SOLUTION: In a series of the production step of the grain-oriented magnetic steel sheet, a slab comprising, by mass, ≤0.08% C, 2.0-8.0% Si, 0.005-1.0% Mn, ≤150 ppm Al, ≤50 ppm each of N, S and Se and the balance being Fe and unavoidable impurities is subjected to hot rolling, subsequently to cold rolling either once or two or more times interrupted by intermediate annealing and subsequently to finish annealing. Here, finish annealing is performed without applying the annealing separator to the steel sheet after recrystallization annealing. The maximum temperature in finish annealing is kept below a prescribed temperature, and the average heating rate for heating the steel sheet from 700°C to the maximum temperature in finish annealing and the average cooling rate for cooling the steel sheet from the maximum temperature to 700°C are each controlled to ≤30°C/h. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００１７】
＜実験３＞
表１に記載される鋼１および鋼５の成分組成になる鋼スラブを、１２００℃でスラブ加熱し、熱間圧延により２．６ｍｍの厚さに仕上げ、その後９５０℃で６０秒の熱延板焼鈍を施した後、冷間圧延により０．３ｍｍの厚さに仕上げた。さらに、９００℃で１０秒の再結晶焼鈍を施した。この際、焼鈍雰囲気の露点を−１０〜４０℃の範囲で種々に変化させた。再結晶焼鈍後の鋼板表層を観察すると、乾燥雰囲気ではサブスケールの形成・発達が認められなかったが、露点が高くなるにつれてシリカを主体としたサブスケールが発達していた。その後、焼鈍分離剤を塗布することなく、７５時間保定する仕上焼鈍を施した。その際、前記種々に露点を変更して作製した再結晶焼鈍板の各々について最高到達温度を１０００〜１３００℃まで変更し、７００℃から最高到達温度までの範囲内の昇温速度および冷却速度の平均を各々３０℃／ｈとした。
【００１８】
この仕上焼鈍後にコイルを巻き直しして、鋼板同士が癒着しているかを調査した。そして、仕上焼鈍後に鋼板の密着が認められなかった鋼板について、その仕上焼鈍温度の最高温度と仕上焼鈍前の鋼板のサブスケール厚みとの関係を表２に示す。この結果から、露点０℃超の湿潤雰囲気として仕上焼鈍前の鋼板にサブスケールを０．２ｍｍ厚以上発達させれば、Ｂｉ等を含有させない場合でも、仕上焼鈍の温度が１１００℃でも、鋼板の密着が発生しないことが明らかとなった。
【００１９】
【表２】

【００２０】
発明者らは、以上の実験結果から、インヒビターを含まない成分系において、焼鈍分離剤を適用せずに仕上焼鈍を施す上で問題となる、鋼板同士の密着を仕上焼鈍の昇温速度および冷却速度を規定することで効果的に防止し、安定して製造できることを新規に知見したのである。
本発明は、上記知見に立脚するものである。
【００２１】
すなわち、本発明の要旨構成は次のとおりである。
（１）質量比で、
Ｃ：０．０８％以下、
Ｓｉ：２．０％〜８．０％および
Ｍｎ：０．００５〜１．０％
を含み、Ａｌを１５０ｐｐｍ以下、かつＮ、ＳおよびＳｅを各々５０ｐｐｍ以下に低減し、残部Ｆｅおよび不可避不純物からなる、スラブを熱間圧延したのち、１回もしくは中間焼鈍を挟む２回以上の冷間圧延を施し、次いで再結晶焼鈍を行い、その後仕上焼鈍を施す一連の方向性電磁鋼板の製造工程において、
再結晶焼鈍後に焼鈍分離剤を適用することなく仕上焼鈍を施すに当り、仕上焼鈍における最高到達温度について、再結晶焼鈍の雰囲気を露点０℃以下とした場合は前記最高到達温度を１０００℃以下、再結晶焼鈍の雰囲気を露点０℃超とした場合は前記最高到達温度を１１００℃以下とし、かつ仕上焼鈍における７００℃から最高到達温度までの範囲での昇温速度および最高到達温度から７００℃までの範囲での冷却速度の平均値を各々３０℃／ｈ以下とすることを特徴とする方向性電磁鋼板の製造方法。
【００２２】
（２）質量比で、
Ｃ：０．０８％以下、
Ｓｉ：２．０％〜８．０％および
Ｍｎ：０．００５〜１．０％
を含み、さらにＢｉ、Ｓｂ、Ｐｂ、Ｔａ、Ｃａ、Ｃｒ、Ｓｒ、ＳｎおよびＴｅから選ばれる１種または２種以上を各々１０ｐｐｍ以上含有し、Ａｌを１５０ｐｐｍ以下、かつＮ、ＳおよびＳｅを各々５０ｐｐｍ以下に低減し、残部Ｆｅおよび不可避不純物からなる、スラブを熱間圧延したのち、１回もしくは中間焼鈍を挟む２回以上の冷間圧延を施し、次いで再結晶焼鈍を行い、その後仕上焼鈍を施す一連の方向性電磁鋼板の製造工程において、
再結晶焼鈍後に焼鈍分離剤を適用することなく仕上焼鈍を施すに当り、仕上焼鈍における最高到達温度を１３００℃以下とし、かつ仕上焼鈍における７００℃から最高到達温度までの範囲での昇温速度および最高到達温度から７００℃までの範囲での冷却速度の平均値を各々３０℃／ｈ以下とすることを特徴とする方向性電磁鋼板の製造方法。
【００２３】
（３）再結晶焼鈍後の鋼板表層に、けい素酸化物を主体としたサブスケールを０．２μｍ 以上の厚みで形成することを特徴とする上記（１）または（２）に記載の電磁鋼板の製造方法。
【００２４】
（４）スラブが、さらに質量比で
Ｎｉ：０．０１〜１．５０％、
Ｃｕ：０．０１〜０．５０％および
Ｐ：０．００５〜０．５０％から選ばれる１種または２種以上を含有することを特徴とする上記（１）、（２）または（３）に記載の電磁鋼板の製造方法。
【００２５】
【発明の実施の形態】
次に、本発明の構成要件における限定理由について述べる。
まず、本発明の電磁鋼板を製造する際の溶鋼成分の限定理由を、以下に説明する。なお、本明細書において鋼組成を表す％は、特にことわらない限り質量％を意味するものである。
Ｃ：０．０８％以下、
Ｃは、０．０８％を超えると、脱炭処理を行っても磁気時効の起こらない５０ｐｐｍ以下に低減することが困難になるため、０．０８％以下に限定する。
【００２６】
Ｓｉ：２．０％〜８．０％
Ｓｉは、電気抵抗を高めて鉄損を改善する効果があるが、２．０％未満であるとその効果に乏しく、また高温でγ変態を生じて熱延組織が変化したり、仕上焼鈍で変態して結晶方位が変化したりするため、良好な磁気特性が得られない。一方、８．０％を超えると加工性が劣化し、飽和磁束密度も低下するため、２．０％〜８．０％とする。
【００２７】
Ｍｎ：０．００５〜１．０％
Ｍｎは、熱間加工性を良好にするために必要な元素であるが、０．００５％未満であると効果がなく、一方１．０％を超えると製品板の磁束密度が低下するため、０．００５〜１．０％とする。
【００２８】
Ａｌを１５０ｐｐｍ以下、かつＮ、ＳおよびＳｅを各々５０ｐｐｍ以下
インヒビター元素であるＡｌは１５０ｐｐｍ以下、かつＮ、ＳおよびＳｅ については５０ｐｐｍ以下に低減することが、本発明において鋼板を良好に二次再結晶させる上で必須である。かかる成分は、極力低減することが磁気特性の観点からは望ましく、例えばＡｌとしては１００ｐｐｍ以下がより好ましい。しかし、これらの成分を低減するためにはコスト高となる場合があることから、上記範囲内で残存させても問題はない。
【００２９】
Ｂｉ、Ｓｂ、Ｐｂ、Ｔａ、Ｃａ、Ｃｒ、Ｓｒ、ＳｎおよびＴｅから選ばれる１種または２種以上を各々１０ｐｐｍ以上
また、Ｂｉ、Ｓｂ、Ｐｂ、Ｔａ、Ｃａ、Ｃｒ、Ｓｒ、ＳｎおよびＴｅから選ばれる１種または２種以上を含有させることで、かかる元素およびその化合物が表層に濃化そして析出し、鋼板同士が接触した際においても鋼（地鉄）そのものの接触が回避され、１３００℃までの高温仕上焼鈍においても鋼板同士の密着を抑制する効果が見込まれることから有効である。ただし、含有量が多いと材料コストが増加するために多量に含有させる必要はない。
【００３０】
その他の窒化物形成元素である、Ｔｉ、Ｎｂ、Ｂ、Ｖ等についても、それぞれ５０ｐｐｍ以下に低減することが、鉄損の劣化を防いで良好な加工性を確保する上で有効である。
【００３１】
さらに、熱延板組織を改善して磁気特性を向上させるために、Ｎｉを添加することができる。その添加量が０．００５％未満であると磁気特性の向上量が小さく、一方１．５０％を超えると二次再結晶が不安定になり磁気特性が劣化するため、添加量は、０．００５〜１．５０％とする。
【００３２】
さらにまた、鉄損を向上させる目的で、Ｃｕ：Ｏ．０１〜０．５０％およびＰ：Ｏ．００５〜０．５０％のうちのいずれか一種を単独で、または２種を複合して添加できる。それぞれ添加量が下限量より少ない場合には鉄損向上効果がなく、一方上限量を超えると二次再結晶粒の発達が抑制される。
【００３３】
上記成分を有する溶鋼は、通常の造塊法や連続鋳造法でスラブとしてもよいし、１００ｍｍ以下の厚さの薄鋳片を直接鋳造法で製造してもよい。スラブは通常の方法で加熱して熱間圧延するが、鋳造後加熱せずに直ちに熱間圧延してもよい。薄鋳片の場合には、熱間圧延しても良いし、熱間圧延を省略してそのまま以後の工程に進んでもよい。熱間圧延前のスラブ加熱温度は従来必須であったインヒビターを固溶させるための高温焼鈍を必要としないことから、１２５０℃以下の低温とすることがコストの面で望ましい。
【００３４】
次いで、必要に応じて熱延板焼鈍を施す。ゴス組織を製品板において高度に発達させるためには、熱延板焼鈍温度は８００℃以上１１００℃以下が好適である。熱延板焼鈍温度が８００℃未満であると熱延でのバンド組織が残留し、整粒の一次再結晶組織を実現することが困難になり二次再結晶の発達が阻害される。熱延板焼鈍温度が１１００℃を超えると、熱延板焼鈍後の粒径が粗大化しすぎることため、整粒の一次再結晶組織を実現する上で極めて不利である。
【００３５】
熱延板焼鈍後は、必要に応じて中間焼鈍を挟む１回以上の冷間圧延を施した後、再結晶焼鈍を行う。冷間圧延の温度を１００℃〜２５０℃に上昇させて行うこと、および冷間圧延途中で１００〜２５０℃の範囲での時効処理を１回または複数回行うことが、ゴス組織を発達させる点で有効である。
【００３６】
再結晶焼鈍は、脱炭を必要とする場合に雰囲気を露点が０℃超である湿潤雰囲気とするが、脱炭を必要としない場合、露点が０℃以下の乾燥雰囲気で行っても良い。湿潤雰囲気の場合、けい素酸化物を主体とするサブスケールが形成することがあるが、サブスケールの存在により鋼板同士が接触した際でも鋼（地鉄）そのものの接触が回避され、サブスケールを０．２μｍ 、好ましくは０．８μｍ 、より好ましくは１．８μｍの厚さに形成することにより、高温での仕上焼鈍においても鋼板相互の密着を防止でき有効である。
【００３７】
ここで、けい素酸化物を主体とするサブスケールとは、ＳｉＯ_２およびＦｅＳｉｘＯｙで表されるＦｅ−Ｓｉ酸化物（例えば、ファイアライト、クリノフェロシライト等）が９割以上で構成された内部酸化層である。
【００３８】
また、再結晶焼鈍後にＣ量を１００〜２５０ｐｐｍに調節することにより、磁束密度を向上させることができる。さらに、再結晶焼鈍後は、浸珪法によってＳｉ量を増加させる技術を併用してもよい。その後、焼鈍分離剤を適用することなく仕上焼鈍を施す。
【００３９】
ここで、焼鈍分離剤の適用とは、水に懸濁させたＭｇＯ、シリカ、アルミナ等の鋼板への塗布や、耐熱無機材料シート（シリカ、アルミナ、マイカ）を鋼板の間に挟む様に、なんらかの薬剤もしくは無機・有機材料を鋼板に塗布、電着、接着し、コイル状にして巻き込むことあるいはコイル状に巻いた際に鋼板の間にそれらを装入もしくは注入させることを意味する。
なお、再結晶焼鈍の際に鋼板表層に酸化物等（ＳｉＯ_２、ＦｅＳｉＯ_３等）のサブスケールが不可避的に生成することは、焼鈍分離剤を適用したことにはならない。
【００４０】
その後、二次再結晶を発現させるために仕上焼鈍を施す。仕上焼鈍における昇温速度および冷却速度は上述の理由により７００℃から仕上焼鈍での最高到達温度までの平均で３０℃／ｈ以下にする必要がある。仕上焼鈍は、最高到達温度に達する過程で一次保定および二次保定と呼ばれる、各々一定の温度で段階的に数時間ずつ保定する場合がある。この保定も鋼板の密着に影響するので、本発明ではこれら保定時間も込みで計算した速度を、昇温速度および冷却速度とする。ただし、最高到達温度での保定時間は含めず、７００℃から最高到達温度に達した時点までの時間で昇温速度を計算する。
【００４１】
また、仕上焼鈍は二次再結晶発現のために７５０℃以上で行う必要があるが、特に二次再結晶を完了させるために８００℃以上の温度で３０時間以上保持させることが望ましい。
【００４２】
仕上焼鈍後には、平坦化焼鈍を行って張力を付加して形状を矯正することが、鉄損低減のために有効である。また、平坦化焼鈍を湿潤雰囲気で行い脱炭を行ってもよい。鋼板を積層して使用する場合には、鉄損を改善するために、平坦化焼鈍後、鋼板表面に絶縁コーティングを施すことが有効である。良好な打抜き性を確保するためには樹脂を含有する有機系コーティングが望ましく、溶接性を重視する場合には無機系コーティングを適用することが望ましい。
【００４３】
なお、本発明における方向性電磁鋼板とは、二次再結晶により結晶粒を発現させた電磁鋼板を意味する。よって、Ｇｏｓｓ方位のみでなくＣｕｂｅ方位（｛１００｝＜００１＞方位もしくは｛１００｝＜０１１＞方位）が二次再結晶している場合も、本発明の対象とする。
【００４４】
【実施例】
実施例１
Ｃ：０．０４３％、Ｓｉ：３．３１％、Ｍｎ：０．０６０％、Ａｌ：３２ｐｐｍ、Ｎ：２７ｐｐｍ、Ｓ：１６ｐｐｍおよびＳｂ：０．０３２％を含み、残部が鉄および不可避的不純物からなるスラブを、連続鋳造にて製造した。ついで、１２００℃に加熱した後、熱間圧延により板厚１．８ｍｍの熱延板に仕上げ、９２５℃で６０秒の熱延板焼鈍を施した。その後、冷間圧延により板厚０．１５ｍｍに仕上げた後、８６０℃で６０秒、露点が２５℃の湿潤雰囲気下で再結晶焼鈍を施した。この再結晶焼鈍後には、鋼板にけい素酸化物を主体としたサブスケールが形成していた。
【００４５】
さらに、焼鈍分離剤を適用することなく、窒素雰囲気中で最高到達温度１０００℃の仕上焼鈍を施した。最高到達温度での保定時間は５時間とし、かつその昇温過程の８５０℃で３０時間の保定を行った。この際、７００℃から１１５０℃に昇温するときの平均昇温速度と、１１５０℃から７００℃に冷却する際の冷却速度とを、表３に記載のとおり種々に変化させた。冷却後に、鋼板コイルを巻き直すことで鋼板同士の密着の有無を調査した。その結果を、表３に併記する。鋼板同士が密着していない場合は○、密着した場合は×で示した。
同表から明らかなように、本発明に従って製造した場合は、鋼板同士の密着が発生しなかった。
【００４６】
【表３】

【００４７】
実施例２
表４に示す成分を含み、残部が鉄および不可避的不純物からなるスラブを、連続鋳造にて製造した。その後、１１００℃で２０分加熱後、熱間圧延により板厚２．８ｍｍの熱延板に仕上げた。引き続き、９００℃で３０秒の熱延板焼鈍を施し、冷間圧延により板厚０．３５ｍｍに仕上げた後、９５０℃で１０秒、露点が−４５℃の乾燥雰囲気下で再結晶焼鈍を施した。この再結晶焼鈍後には、鋼板にサブスケールは形成していなかった。
【００４８】
その後、焼鈍分離剤を適用することなく、窒素雰囲気中で最高到達温度９００℃で７５時間の仕上焼鈍を施した。ここで、７００〜９００℃間の平均昇温速度を表４に記載のごとく変化させ、同温度域での冷却速度は１５℃／ｈに制御した。冷却後に、鋼板コイルを巻き直すことで鋼板同士の密着の有無を調査した。その結果を、表４に併記する。鋼板同士が密着していない場合は○、密着した場合は×で示した。
同表から明らかなように、本発明に従って製造した場合は、鋼板同士の密着が発生しなかった。
【００４９】
【表４】

【００５０】
実施例３
表５に示す成分を含み、残部が鉄および不可避的不純物からなるスラブを、連続鋳造にて製造した。その後、１２５０℃で３０分加熱後熱間圧延により板厚２．８ｍｍの熱延板に仕上げ、続いて冷間圧延により０．７５ｍｍ厚の板厚とした。さらに、１１００℃で３０秒の熱延板焼鈍を施し、２００℃の温間圧延により板厚０．２７ｍｍに仕上げた後、８３０℃で６０秒、露点が４０℃の湿潤雰囲気下で再結晶焼鈍を施した。この再結晶焼鈍後には、鋼板にけい素酸化物を主体としたサブスケールが形成していた。
【００５１】
その後、焼鈍分離剤を適用することなく、８４０℃で２５時間、窒素雰囲気中で保定後、最高到達温度１１００℃で２０時間、Ａｒ雰囲気で保定する仕上焼鈍を施した。ここで、７００〜１１００℃間の平均昇温速度は１５℃／ｈに制御し、同温度域での冷却速度は表５に記載のごとく変化させた。冷却後に、鋼板コイルを巻き直すことで鋼板同士の密着の有無を調査した。その結果を表５に併記する。鋼板同士が密着していない場合は○、密着した場合は×で示した。
同表から明らかなように、本発明に従って製造した場合は、鋼板同士の密着が発生しなかった。
【００５２】
【表５】

【００５３】
実施例４
表４に示した鋼Ａ、ＢおよびＣの成分を有する熱延板に、１０００℃で９０秒の熱延板焼鈍を施し、冷間圧延により板厚０．５０ｍｍに仕上げた後、９００℃で１０秒の再結晶焼鈍を施した。この際、露点については１条件は−５０℃の乾燥雰囲気で、もう１条件は５０℃の湿潤雰囲気とした。乾燥雰囲気での再結晶焼鈍後には鋼板にサブスケールは形成していなかったが、湿潤雰囲気では約１μｍ の厚さのサブスケールが認められた。
【００５４】
その後、焼鈍分離剤を適用することなく、昇温並びに冷却過程ではＡｒ雰囲気、保定時はＨ_２雰囲気の仕上焼鈍を施した。仕上焼鈍の最高到達温度を、９００、１０００、１１００、１２００、１３００℃と変化させ、それぞれの温度での保定時間は１５時間とした。７００℃から最高到達温度までの平均昇温速度は３０℃／ｈおよび同温度範囲での冷却速度は１５℃／ｈに制御した。冷却後に、鋼板コイルを巻き直すことで鋼板同士の密着の有無を調査した。その結果を表６に示す。鋼板同士が密着していない場合は○、密着した場合は×で示した。
同表から明らかなように、本発明に従って製造した場合は、鋼板同士の密着が発生しなかった。
【００５５】
【表６】

【００５６】
【発明の効果】
本発明によれば、インヒビター成分を有しない素材を用いて方向性電磁鋼板を製造する際に、焼鈍分離剤を適用することなく仕上焼鈍を施す場合においても、鋼板同士の密着が回避されるから、安定して方向性電磁鋼板を製造することができる。
【図面の簡単な説明】
【図１】仕上焼鈍における７００℃から最高到達温度までの平均昇温速度および冷却速度を変化させた場合の、仕上焼鈍後の鋼板同士の密着の有無を示した図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing a grain-oriented electrical steel sheet suitable for a core material of a transformer or a rotary machine.
[0002]
[Prior art]
For grain-oriented electrical steel sheets, it is a common technique to use secondary precipitates called inhibitors to secondary recrystallize grains having Goss orientation during finish annealing. For example, the method of using AlN and MnS described in Patent Document 1 and the method of using MnS and MnSe described in Patent Document 2 have been industrially put into practical use. Apart from these, Patent Document 3 describes a technique of adding CuSe and BN, and Patent Document 4 describes a method using a nitride of Ti, Zr, and V, respectively.
[0003]
The method using these inhibitors is a useful method for stably developing secondary recrystallized grains.However, since the inhibitor causes deterioration of the magnetic properties after the secondary recrystallization, the finish annealing is performed. It was necessary to remove precipitates and inclusions such as inhibitors from the ground iron by controlling the atmosphere at a high temperature of 1100 ° C. or higher.
[0004]
In view of this, the inventors proposed in Patent Document 5 a technique for developing Goss-oriented crystal grains by secondary recrystallization in a material that does not contain an inhibitor component. In this method, since the step of purifying the inhibitor is unnecessary, there is no need to increase the temperature of the finish annealing, and this method has great advantages both in terms of cost and maintenance.
[0005]
By the way, in the manufacture of grain-oriented electrical steel sheets, when the finish annealing is at a high temperature, it is necessary to apply an annealing separator before the finish annealing in order to prevent the steel sheets from sticking to each other. As this annealing separator, MgO is mainly used in order to form forsterite in the next step. In addition, silica or alumina suspended in water is applied, or a heat resistant inorganic material sheet (silica, alumina, mica) is sandwiched between steel plates. In this case, the cost of the equipment for applying the separating agent and the cost of its maintenance are incurred together with the cost of the annealing separating agent, and the problem is that the cost becomes high.
[0006]
Therefore, if a technique using a material that does not contain the above inhibitor components is established, it is expected that an annealing separator is unnecessary as a result of the need for a high-temperature finish annealing and a reduction in the finish annealing temperature. It was. However, despite the fact that finish annealing is performed at a low temperature, a problem has arisen that steel sheets often adhere to each other.
[0007]
[Patent Document 1]
Japanese Patent Publication No. 40-15644 [Patent Document 2]
Japanese Patent Publication No. 51-13469 [Patent Document 3]
Japanese Patent Publication No. 58-42244 [Patent Document 4]
Japanese Patent Publication No. 46-40855 [Patent Document 5]
Japanese Patent Laid-Open No. 2000-129356
[Problems to be solved by the invention]
In the production of grain-oriented electrical steel sheets that do not use an inhibitor, the present invention establishes a manufacturing technique that avoids the problem of adhesion between steel sheets during finish annealing even when an annealing separator is not applied. An object of the present invention is to provide a low-cost production method that does not apply a separating agent.
[0009]
[Means for Solving the Problems]
The inventors have found that the adhesion of the steel sheet can be effectively prevented by prescribing the conditions of finish annealing without applying an expensive annealing separator, and completed the method for producing the electrical steel sheet of the present invention. .
[0010]
That is, as a result of intensive research on solving such problems, the inventors have determined the components in steel and reduced the inhibitor components by appropriately adjusting the heating rate and cooling rate of finish annealing. And also when not applying an annealing separation agent, it discovered that the adhesion | attachment of the steel plates at the time of finish annealing can be prevented effectively.
In the following, the present invention will be described based on experiments that have resulted in success.
[0011]
<Experiment 1>
In mass%, C: 0.0021%, Si: 3.31%, Mn: 0.060%, sol. A steel slab containing Al: 56 ppm, N: 27 ppm, S: 16 ppm and Bi: 0.022% was manufactured by continuous casting, heated to 1160 ° C., and then finished to a thickness of 2.6 mm by hot rolling. Thereafter, hot-rolled sheet annealing was performed at 950 ° C. for 60 seconds, and then finished to a thickness of 0.35 mm by cold rolling.
Further, after recrystallization annealing at 830 ° C. for 60 seconds and a dew point of 35 ° C., finish annealing was performed for 5 hours at 1200 ° C. which is the highest temperature without applying an annealing separator. At this time, the rate of temperature increase in the range from 700 ° C. to the highest temperature and the subsequent cooling rate in the same temperature range were changed to various rates.
[0012]
Next, after finishing annealing, the coil was rewound to investigate whether the steel plates were in close contact with each other. The survey results are shown in FIG. In FIG. 1, ○ indicates that the steel plates are not in close contact with each other, × indicates that the steel plates are in close contact (if the steel plates are partially adhered, the state is “adhered”. Each of which is defined). From this result, it became clear that the adhesion of the steel sheet does not occur when the temperature raising rate and the cooling rate of the finish annealing are 30 ° C./h or less.
[0013]
Here, when the temperature raising rate and the cooling rate of finish annealing are 30 ° C./h or less, the reason why the steel sheet does not adhere is not necessarily clear, but can be considered as follows.
That is, the conditions for the steel sheets to be in close contact include (1) the annealing temperature is high, (2) the annealing time is long, and (3) the steel sheets are pressed against each other with a large pressure. It is considered that the heating rate and the cooling rate of annealing have an influence on (3). Usually, finish annealing is performed by so-called box annealing, in which a steel sheet is annealed in a coil shape. In this case, a slight deviation occurs between the temperature change of the annealing furnace and the temperature change of the coil itself. Further, since the steel coil has a cylindrical shape having a certain size, a temperature difference is generated between the outside and the inside thereof. As a result of the difference in the thermal expansion of the steel due to the temperature difference between the inside and outside, it is expected that compressive stress is applied to a specific part of the coil. When the temperature increase rate and / or cooling rate of finish annealing is higher than 30 ° C / h, the temperature difference of each part of the coil becomes large, so that a large compressive stress is applied to a specific part to promote the adhesion of the steel sheet. It is considered to be done.
[0014]
<Experiment 2>
A steel slab having Al reduced to 100 ppm or less, N, S, and Se reduced to 50 ppm or less and having the components described in Table 1 was heated at 1120 ° C. and finished to a thickness of 2.4 mm by hot rolling, and then 950 After hot-rolled sheet annealing at 60 ° C. for 60 seconds, it was finished to a thickness of 0.35 mm by cold rolling. Further, after recrystallization annealing at 900 ° C. for 10 seconds and a dew point of −40 ° C., 75 hours at each of the maximum attained temperatures of 1000 ° C., 1100 ° C., and 1200 ° C. without applying an annealing separator. Finishing annealing was performed. Under the present circumstances, the average of the temperature increase rate and the cooling rate in the range from 700 degreeC to each maximum temperature of 1000 degreeC, 1100 degreeC, and 1200 degreeC was 30 degreeC / h, respectively.
[0015]
Then, after the finish annealing, the coil was rewound to investigate whether the steel plates were in close contact with each other. The results are also shown in Table 1. In Table 1, the case where the steel plates are not in close contact is indicated by ◯, and the case where they are in close contact is indicated by x. As a result, when any of Bi, Sb, Pb, Ta, Ca, Cr, Sr, Sn, and Te is contained in the slab component, it can be seen that the steel plates do not adhere to each other even in the finish annealing at a high temperature of 1100 ° C. or higher. .
[0016]
[Table 1]

[0017]
<Experiment 3>
A steel slab having the composition of steel 1 and steel 5 listed in Table 1 is heated at 1200 ° C. to a thickness of 2.6 mm by hot rolling, and then hot-rolled at 950 ° C. for 60 seconds. After annealing, it was finished to a thickness of 0.3 mm by cold rolling. Further, recrystallization annealing was performed at 900 ° C. for 10 seconds. Under the present circumstances, the dew point of annealing atmosphere was changed variously in the range of -10-40 degreeC. When the surface layer of the steel sheet after recrystallization annealing was observed, subscale formation / development was not observed in a dry atmosphere, but as the dew point increased, the subscale mainly composed of silica developed. Then, the finish annealing which hold | maintains for 75 hours was given, without apply | coating an annealing separation agent. At that time, the maximum reached temperature was changed from 1000 to 1300 ° C. for each of the recrystallized annealed plates produced by changing the dew point in various ways, and the heating rate and cooling rate within the range from 700 ° C. to the maximum reached temperature were changed. Each average was 30 ° C./h.
[0018]
After the finish annealing, the coil was rewound to investigate whether the steel plates were adhered to each other. Table 2 shows the relationship between the maximum temperature of the finish annealing temperature and the subscale thickness of the steel plate before the finish annealing for the steel plates in which the adhesion of the steel plates was not recognized after the finish annealing. From this result, if the subscale is developed to a thickness of 0.2 mm or more in the steel sheet before finish annealing as a wet atmosphere with a dew point exceeding 0 ° C., even if Bi is not contained, even if the temperature of finish annealing is 1100 ° C., It became clear that adhesion did not occur.
[0019]
[Table 2]

[0020]
From the above experimental results, the inventors have found that, in a component system that does not contain an inhibitor, the problem of the finish annealing without applying the annealing separator, the adhesion between the steel plates, the heating rate of the finish annealing and the cooling It was newly found out that it is possible to effectively prevent and regulate stably by defining the speed.
The present invention is based on the above findings.
[0021]
That is, the gist configuration of the present invention is as follows.
(1) By mass ratio,
C: 0.08% or less,
Si: 2.0% to 8.0% and Mn: 0.005 to 1.0%
And after reducing the temperature of Al to 150 ppm or less and reducing each of N, S and Se to 50 ppm or less and comprising the remaining Fe and inevitable impurities, the slab is hot-rolled and then cooled once or two times with intermediate annealing. In the manufacturing process of a series of grain-oriented electrical steel sheets that are subjected to hot rolling, then recrystallized annealing, and then finish annealing,
In performing the final annealing without applying the annealing separator after the recrystallization annealing, when the recrystallization annealing atmosphere is the dew point of 0 ° C. or less, the maximum reached temperature is 1000 ° C. or less, When the atmosphere of recrystallization annealing is dew point over 0 ° C, the maximum temperature reached is 1100 ° C or less, and the rate of temperature increase in the range from 700 ° C to the maximum temperature in finish annealing and from the maximum temperature to 700 ° C A method for producing a grain-oriented electrical steel sheet, characterized in that an average value of cooling rates in the range of 30 ° C./h or less is set for each.
[0022]
(2) By mass ratio,
C: 0.08% or less,
Si: 2.0% to 8.0% and Mn: 0.005 to 1.0%
Further containing 10 ppm or more each of one or more selected from Bi, Sb, Pb, Ta, Ca, Cr, Sr, Sn and Te, Al 150 ppm or less, and N, S and Se respectively Reduced to 50 ppm or less, consisting of the remainder Fe and inevitable impurities, hot-rolled the slab, then subjected to one or more cold rolling sandwiched by intermediate annealing, followed by recrystallization annealing, and then finish annealing In the manufacturing process of a series of grain-oriented electrical steel sheets to be applied,
In performing finish annealing without applying an annealing separator after recrystallization annealing, the maximum temperature reached in finishing annealing is set to 1300 ° C. or less, and the rate of temperature rise in the range from 700 ° C. to the maximum temperature reached in finishing annealing A method for producing a grain-oriented electrical steel sheet, characterized in that an average value of cooling rates in a range from the highest temperature to 700 ° C. is 30 ° C./h or less.
[0023]
(3) The electrical steel sheet according to (1) or (2) above, wherein a subscale mainly composed of silicon oxide is formed in a thickness of 0.2 μm or more on the surface layer of the steel sheet after recrystallization annealing. Manufacturing method.
[0024]
(4) The slab further has a mass ratio of Ni: 0.01 to 1.50%,
The above (1), (2) or (3) characterized by containing one or more selected from Cu: 0.01 to 0.50% and P: 0.005 to 0.50% The manufacturing method of the electrical steel sheet as described in 2.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Next, the reason for limitation in the constituent requirements of the present invention will be described.
First, the reason for limitation of the molten steel component at the time of manufacturing the electrical steel sheet of the present invention will be described below. In the present specification, “%” representing a steel composition means “% by mass” unless otherwise specified.
C: 0.08% or less,
If C exceeds 0.08%, it is difficult to reduce it to 50 ppm or less at which magnetic aging does not occur even if decarburization treatment is performed. Therefore, C is limited to 0.08% or less.
[0026]
Si: 2.0% to 8.0%
Si has the effect of increasing the electrical resistance and improving the iron loss. However, if it is less than 2.0%, the effect is poor, and the γ transformation is caused at a high temperature to change the hot-rolled structure, or the finish annealing. Since the crystal orientation changes due to transformation, good magnetic properties cannot be obtained. On the other hand, if it exceeds 8.0%, the workability deteriorates and the saturation magnetic flux density also decreases, so the content is set to 2.0% to 8.0%.
[0027]
Mn: 0.005 to 1.0%
Mn is an element necessary for improving the hot workability, but if it is less than 0.005%, there is no effect, while if it exceeds 1.0%, the magnetic flux density of the product plate decreases. 0.005 to 1.0%.
[0028]
Al is 150 ppm or less, and N, S, and Se are each 50 ppm or less. The inhibitor element Al is reduced to 150 ppm or less, and N, S, and Se 2 are reduced to 50 ppm or less. Essential for crystallization. Such components are desirably reduced as much as possible from the viewpoint of magnetic properties, and for example, Al is more preferably 100 ppm or less. However, in order to reduce these components, the cost may increase, so there is no problem even if they are left within the above range.
[0029]
One or two or more selected from Bi, Sb, Pb, Ta, Ca, Cr, Sr, Sn and Te are each 10 ppm or more. Also from Bi, Sb, Pb, Ta, Ca, Cr, Sr, Sn and Te By including one or two or more selected ones, such elements and their compounds are concentrated and precipitated on the surface layer, and even when the steel plates are in contact with each other, the contact of the steel (base metal) itself is avoided, and 1300 ° C. Even in the high-temperature finish annealing up to, it is effective because the effect of suppressing the adhesion between the steel plates is expected. However, if the content is large, the material cost increases, so it is not necessary to contain a large amount.
[0030]
For other nitride forming elements such as Ti, Nb, B, and V, reduction to 50 ppm or less is effective in preventing deterioration of iron loss and ensuring good workability.
[0031]
Furthermore, Ni can be added to improve the hot rolled sheet structure and improve the magnetic properties. If the amount added is less than 0.005%, the amount of improvement in magnetic properties is small. On the other hand, if it exceeds 1.50%, secondary recrystallization becomes unstable and the magnetic properties are deteriorated. 005 to 1.50%.
[0032]
Furthermore, for the purpose of improving iron loss, Cu: O. 01-0.50% and P: O. Any one of 005 to 0.50% can be added alone or in combination of two. When the addition amount is less than the lower limit amount, there is no effect of improving iron loss, while when the upper limit amount is exceeded, the development of secondary recrystallized grains is suppressed.
[0033]
The molten steel having the above components may be formed into a slab by a normal ingot-making method or a continuous casting method, or a thin cast piece having a thickness of 100 mm or less may be produced by a direct casting method. The slab is heated and hot-rolled by a normal method, but may be immediately hot-rolled without being heated after casting. In the case of a thin slab, hot rolling may be performed, or the hot rolling may be omitted and the process may proceed as it is. Since the slab heating temperature before hot rolling does not require high-temperature annealing for dissolving the inhibitor, which has been indispensable in the past, a low temperature of 1250 ° C. or lower is desirable in terms of cost.
[0034]
Next, hot-rolled sheet annealing is performed as necessary. In order to highly develop a goth structure in the product plate, the hot-rolled sheet annealing temperature is preferably 800 ° C. or higher and 1100 ° C. or lower. When the hot-rolled sheet annealing temperature is less than 800 ° C., a band structure in hot rolling remains, and it becomes difficult to realize a primary recrystallized structure of sized particles, thereby inhibiting the development of secondary recrystallization. When the hot-rolled sheet annealing temperature exceeds 1100 ° C., the grain size after the hot-rolled sheet annealing is excessively coarsened, which is extremely disadvantageous in realizing a primary recrystallized structure of sized particles.
[0035]
After hot-rolled sheet annealing, recrystallization annealing is performed after performing one or more cold rolling sandwiching intermediate annealing as necessary. The fact that the temperature of cold rolling is raised to 100 ° C. to 250 ° C. and that the aging treatment in the range of 100 to 250 ° C. is performed once or a plurality of times during the cold rolling develops a goth structure. It is effective in.
[0036]
In the recrystallization annealing, when decarburization is required, the atmosphere is a wet atmosphere with a dew point exceeding 0 ° C. However, when decarburization is not required, it may be performed in a dry atmosphere with a dew point of 0 ° C. or less. In a humid atmosphere, subscales mainly composed of silicon oxide may form. However, even when steel plates contact each other due to the presence of subscales, the contact of steel (ground iron) itself is avoided, and By forming the film to a thickness of 0.2 μm, preferably 0.8 μm, more preferably 1.8 μm, it is effective to prevent the steel sheets from being adhered to each other even during finish annealing at a high temperature.
[0037]
Here, the sub-scale mainly composed of silicon oxide is an internal oxidation composed of 90% or more of Fe—Si oxide (for example, firelite, clinoferosilite, etc.) represented by SiO ₂ and FeSixOy. Is a layer.
[0038]
Moreover, magnetic flux density can be improved by adjusting C amount to 100-250 ppm after recrystallization annealing. Furthermore, after recrystallization annealing, a technique for increasing the amount of Si by a silicon immersion method may be used in combination. Then, finish annealing is performed without applying an annealing separator.
[0039]
Here, the application of the annealing separator is applied to steel plates such as MgO, silica, and alumina suspended in water, and a heat resistant inorganic material sheet (silica, alumina, mica) is sandwiched between the steel plates, It means that some chemical agent or inorganic / organic material is applied to a steel plate, electrodeposited, adhered and wound in a coil shape, or when it is wound in a coil shape, it is charged or injected between the steel plates.
In addition, the fact that subscales such as oxides (SiO ₂ , FeSiO _3, etc.) are inevitably formed on the steel sheet surface layer during recrystallization annealing does not mean that the annealing separator has been applied.
[0040]
Thereafter, finish annealing is performed to develop secondary recrystallization. The temperature raising rate and the cooling rate in the finish annealing need to be 30 ° C./h or less on average from 700 ° C. to the highest temperature reached in the finish annealing for the reason described above. In the finish annealing, there are cases in which the temperature is kept at a certain temperature for several hours step by step, which is called primary holding and secondary holding in the process of reaching the maximum temperature. Since this retention also affects the adhesion of the steel plates, in the present invention, the speed calculated including these retention times is defined as the heating rate and the cooling rate. However, the temperature rising rate is calculated from the time from 700 ° C. to the time when the maximum temperature is reached, not including the holding time at the maximum temperature.
[0041]
In addition, the finish annealing needs to be performed at 750 ° C. or higher for the purpose of secondary recrystallization. In particular, in order to complete the secondary recrystallization, it is desirable to hold at a temperature of 800 ° C. or higher for 30 hours or more.
[0042]
After the finish annealing, it is effective to reduce the iron loss by performing flattening annealing and adding tension to correct the shape. Further, decarburization may be performed by performing planarization annealing in a humid atmosphere. In the case of using laminated steel plates, in order to improve iron loss, it is effective to apply an insulating coating to the steel plate surface after planarization annealing. In order to ensure good punchability, an organic coating containing a resin is desirable, and when emphasis is placed on weldability, it is desirable to apply an inorganic coating.
[0043]
The grain-oriented electrical steel sheet in the present invention means an electrical steel sheet in which crystal grains are expressed by secondary recrystallization. Therefore, not only the Goss orientation but also the Cube orientation ({100} <001> orientation or {100} <011> orientation) is also subject to the present invention.
[0044]
【Example】
Example 1
C: 0.043%, Si: 3.31%, Mn: 0.060%, Al: 32ppm, N: 27ppm, S: 16ppm and Sb: 0.032%, the balance being from iron and inevitable impurities The resulting slab was manufactured by continuous casting. Then, after heating to 1200 ° C., hot rolled sheet was finished into a hot rolled sheet having a thickness of 1.8 mm by hot rolling, and subjected to hot rolled sheet annealing at 925 ° C. for 60 seconds. Then, after finishing to a plate thickness of 0.15 mm by cold rolling, recrystallization annealing was performed in a humid atmosphere at 860 ° C. for 60 seconds and a dew point of 25 ° C. After this recrystallization annealing, a subscale mainly composed of silicon oxide was formed on the steel sheet.
[0045]
Further, finish annealing was performed at a maximum temperature of 1000 ° C. in a nitrogen atmosphere without applying an annealing separator. The holding time at the maximum temperature reached was 5 hours, and the holding was performed at 850 ° C. for 30 hours in the temperature rising process. At this time, as shown in Table 3, the average heating rate when the temperature was raised from 700 ° C. to 1150 ° C. and the cooling rate when the temperature was cooled from 1150 ° C. to 700 ° C. were variously changed. After cooling, the presence or absence of adhesion between the steel plates was investigated by rewinding the steel plate coil. The results are also shown in Table 3. In the case where the steel plates are not in close contact with each other, it is indicated by ◯, and when the steel plates are in close contact, the cross is indicated by x.
As apparent from the table, when manufactured according to the present invention, the steel plates did not adhere to each other.
[0046]
[Table 3]

[0047]
Example 2
A slab containing the components shown in Table 4 with the balance being iron and inevitable impurities was produced by continuous casting. Then, after heating at 1100 ° C. for 20 minutes, it was finished into a hot-rolled sheet having a thickness of 2.8 mm by hot rolling. Subsequently, hot rolled sheet annealing was performed at 900 ° C. for 30 seconds, and after finishing to a sheet thickness of 0.35 mm by cold rolling, recrystallization annealing was performed at 950 ° C. for 10 seconds in a dry atmosphere with a dew point of −45 ° C. did. Sub-scale was not formed on the steel plate after this recrystallization annealing.
[0048]
Thereafter, a final annealing was performed for 75 hours at a maximum temperature of 900 ° C. in a nitrogen atmosphere without applying an annealing separator. Here, the average temperature increase rate between 700-900 ° C. was changed as described in Table 4, and the cooling rate in the same temperature range was controlled to 15 ° C./h. After cooling, the presence or absence of adhesion between the steel plates was investigated by rewinding the steel plate coil. The results are also shown in Table 4. In the case where the steel plates are not in close contact with each other, it is indicated by ◯, and when the steel plates are in close contact, the cross is indicated by x.
As apparent from the table, when manufactured according to the present invention, the steel plates did not adhere to each other.
[0049]
[Table 4]

[0050]
Example 3
A slab containing the components shown in Table 5 with the balance being iron and inevitable impurities was produced by continuous casting. Thereafter, it was heated at 1250 ° C. for 30 minutes and then finished into a hot-rolled sheet having a thickness of 2.8 mm by hot rolling, and subsequently cold-rolled to a thickness of 0.75 mm. Furthermore, after performing hot-rolled sheet annealing at 1100 ° C. for 30 seconds and finishing to a thickness of 0.27 mm by warm rolling at 200 ° C., recrystallization annealing is performed at 830 ° C. for 60 seconds in a humid atmosphere with a dew point of 40 ° C. Was given. After this recrystallization annealing, a subscale mainly composed of silicon oxide was formed on the steel sheet.
[0051]
Then, without applying an annealing separator, after being held at 840 ° C. for 25 hours in a nitrogen atmosphere, finish annealing was carried out at 20 ° C. for 20 hours at the highest temperature reached 1100 ° C. Here, the average temperature increase rate between 700 and 1100 ° C. was controlled to 15 ° C./h, and the cooling rate in the same temperature range was changed as shown in Table 5. After cooling, the presence or absence of adhesion between the steel plates was investigated by rewinding the steel plate coil. The results are also shown in Table 5. In the case where the steel plates are not in close contact with each other, it is indicated by ◯, and when the steel plates are in close contact, the cross is indicated by x.
As apparent from the table, when manufactured according to the present invention, the steel plates did not adhere to each other.
[0052]
[Table 5]

[0053]
Example 4
The hot-rolled sheet having the components of steels A, B and C shown in Table 4 was subjected to hot-rolled sheet annealing at 1000 ° C. for 90 seconds and finished to a sheet thickness of 0.50 mm by cold rolling, and then at 900 ° C. Recrystallization annealing was performed for 10 seconds. At this time, as for the dew point, one condition was a dry atmosphere at -50 ° C, and the other condition was a wet atmosphere at 50 ° C. No subscale was formed on the steel sheet after recrystallization annealing in a dry atmosphere, but a subscale with a thickness of about 1 μm was observed in a wet atmosphere.
[0054]
Then, without applying an annealing separator, finish annealing was performed in an Ar atmosphere in the temperature rising and cooling process and in an H ₂ atmosphere during holding. The maximum ultimate temperature of finish annealing was changed to 900, 1000, 1100, 1200, 1300 ° C., and the holding time at each temperature was 15 hours. The average rate of temperature increase from 700 ° C. to the highest temperature was controlled at 30 ° C./h, and the cooling rate in the same temperature range was controlled at 15 ° C./h. After cooling, the presence or absence of adhesion between the steel plates was investigated by rewinding the steel plate coil. The results are shown in Table 6. In the case where the steel plates are not in close contact with each other, it is indicated by ◯, and when the steel plates are in close contact, the cross is indicated by x.
As apparent from the table, when manufactured according to the present invention, the steel plates did not adhere to each other.
[0055]
[Table 6]

[0056]
【The invention's effect】
According to the present invention, when a grain-oriented electrical steel sheet is manufactured using a material that does not have an inhibitor component, adhesion between the steel sheets is avoided even when finishing annealing without applying an annealing separator. The grain-oriented electrical steel sheet can be manufactured stably.
[Brief description of the drawings]
FIG. 1 is a diagram showing the presence or absence of adhesion between steel plates after finish annealing when the average temperature rise rate and cooling rate from 700 ° C. to the highest temperature in finish annealing are changed.

Claims (4)

By mass ratio,
C: 0.08% or less,
Si: 2.0% to 8.0% and Mn: 0.005 to 1.0%
And after reducing the temperature of Al to 150 ppm or less and reducing each of N, S and Se to 50 ppm or less and comprising the remaining Fe and inevitable impurities, the slab is hot-rolled and then cooled once or two times with intermediate annealing. In the manufacturing process of a series of grain-oriented electrical steel sheets that are subjected to hot rolling, then recrystallized annealing, and then finish annealing,
In performing the final annealing without applying the annealing separator after the recrystallization annealing, when the recrystallization annealing atmosphere is the dew point of 0 ° C. or less, the maximum reached temperature is 1000 ° C. or less, When the atmosphere of recrystallization annealing is dew point over 0 ° C, the maximum temperature reached is 1100 ° C or less, and the rate of temperature increase in the range from 700 ° C to the maximum temperature in finish annealing and from the maximum temperature to 700 ° C A method for producing a grain-oriented electrical steel sheet, characterized in that an average value of cooling rates in the range of 30 ° C./h or less is set for each. By mass ratio,
C: 0.08% or less,
Si: 2.0% to 8.0% and Mn: 0.005 to 1.0%
Further containing 10 ppm or more each of one or more selected from Bi, Sb, Pb, Ta, Ca, Cr, Sr, Sn and Te, Al 150 ppm or less, and N, S and Se respectively Reduced to 50 ppm or less, consisting of the remainder Fe and inevitable impurities, hot-rolled the slab, then subjected to one or more cold rolling sandwiched by intermediate annealing, followed by recrystallization annealing, and then finish annealing In the manufacturing process of a series of grain-oriented electrical steel sheets to be applied,
In performing finish annealing without applying an annealing separator after recrystallization annealing, the maximum temperature reached in finishing annealing is set to 1300 ° C. or less, and the rate of temperature rise in the range from 700 ° C. to the maximum temperature reached in finishing annealing A method for producing a grain-oriented electrical steel sheet, characterized in that an average value of cooling rates in a range from the highest temperature to 700 ° C. is 30 ° C./h or less. The method for producing an electrical steel sheet according to claim 1 or 2, wherein a subscale mainly composed of silicon oxide is formed on the surface layer of the steel sheet after recrystallization annealing with a thickness of 0.2 µm or more. The slab further has a mass ratio of Ni: 0.01 to 1.50%,
The electrical steel sheet according to claim 1, 2, or 3, characterized by containing one or more selected from Cu: 0.01 to 0.50% and P: 0.005 to 0.50%. Manufacturing method.

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