JP2004315915A

JP2004315915A - Method for depositing insulating film of grain-oriented silicon steel plate

Info

Publication number: JP2004315915A
Application number: JP2003113113A
Authority: JP
Inventors: Katsuyuki Yanagihara; 勝幸柳原; Shuichi Yamazaki; 修一山崎
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 2003-04-17
Filing date: 2003-04-17
Publication date: 2004-11-11
Anticipated expiration: 2023-04-17
Also published as: JP4448287B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a grain-oriented silicon steel plate manufacturing method in which the quality of a finish-annealed film is enhanced without degrading decarburization, and excellent adhesiveness can be consistently obtained when the film tension is increased. <P>SOLUTION: In the grain-oriented silicon steel plate manufacturing method, treatment is performed under a condition that Si concentration on a surface of the steel plate in the heating zone at 800°C is 15-30 mol.% in a decarburization-annealing step of the grain-oriented silicon steel plate. Further, in the grain-oriented silicon steel plate manufacturing method, the average heating speed in the heating zone at 600-800°C is 10-100°C/s, and the ratio P<SB>H2O</SB>/P<SB>H2</SB>is 0.02-0.2 in the decarburization-annealing step. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、一方向性電磁鋼板の表面に、絶縁性および張力付与性の優れた被膜を形成する方法に関する。
【０００２】
【従来の技術】
一方向性電磁鋼板は、（１１０）［００１］を主方位とする結晶組織を有し、磁気鉄心材料として多用されており、エネルギーロスを小さくするために鉄損の小さい材料が求められている。特に、５質量％以下の珪素を含有する一方向性電磁鋼板の鉄損の低減には、鋼板に張力を付与することが有効であり、１５ＭＰａ程度までの張力付与によって、効果的に鉄損を低減できることが知られている。
【０００３】
通常、張力は鋼板表面に形成された被膜により付与されるものであり、従って張力付与には、鋼板より熱膨張係数の小さい材質からなる被膜を高温で鋼板表面に形成することが有効である。これは、鋼板と被膜との間の熱膨張係数差によって生ずる熱応力を利用するものである。
【０００４】
通常の一方向性電磁鋼板の表面には、脱炭焼鈍工程で生ずるＳｉＯ_２を主体とする酸化膜と、焼鈍分離剤として通常用いられるＭｇＯとが、仕上げ焼鈍中に反応して形成されたフォルステライト主体の被膜（以下、仕上げ焼鈍被膜と称する）が存在する。一般的な一方向性電磁鋼板表面への絶縁皮膜の形成方法は、仕上げ焼鈍被膜を残した上で絶縁被膜を施す方法である。仕上げ焼鈍被膜は鋼板に与える張力が大きく、鉄損低減に効果がある。
【０００５】
仕上げ焼鈍被膜には、均一で欠陥が無く、かつ剪断、打ち抜き、および曲げ加工等に耐え得る密着性に優れていることが要求される。特許文献１には、コロイド状シリカと燐酸塩を主体とするコーティング液を鋼板表面に塗布して焼き付けることによって得られる仕上げ焼鈍被膜が開示されており、この被膜は鋼板に対して張力付与の効果が大きく、鉄損低減に有効であることが示されている。
【０００６】
この他に、鋼板上への絶縁被膜の形成による鋼板への張力増大の試みもなされている。例えば特許文献２には、アルミナゾルと硼酸を主体とするコーティング液を鋼板上に焼き付けることによって得られるＡ１_２Ｏ_３−Ｂ_２Ｏ_３系の結晶質被膜が開示されている。該絶縁被膜は、コロイド状シリカと燐酸塩を主体とするコーティングを焼き付けて形成した仕上げ焼鈍被膜と比較して、同一膜厚のもとで１．５〜２倍の被膜張力が得られることが記載されている。
【０００７】
一般に絶縁被膜は、仕上げ焼鈍被膜の上に形成した場合にはかなりの被膜密着性が得られるものの、鉄損低減のために被膜張力をさらに増加させるとその密着性が不十分となるため、より密着性に優れた仕上げ焼鈍被膜の形成が必要となる。
【０００８】
上述のとおり仕上げ焼鈍被膜は、脱炭焼鈍工程で生ずるＳｉＯ_２主体の酸化物を原料の一つとするため、この酸化物の種類や量および分布などが仕上げ焼鈍被膜の機械的強度および鋼板との密着性に影響を及ぼす。従って、良好な仕上げ焼鈍被膜を形成させる上で脱炭焼鈍工程の制御は極めて重要である。
【０００９】
一方向性電磁鋼板の脱炭焼鈍に関しては、例えば特許文献３に開示されているように焼鈍雰囲気の露点を５０〜７０℃に制御する方法、特許文献４に開示されているように脱炭焼鈍後に非酸化性雰囲気中で熱処理を行う方法、特許文献５に開示されているように脱炭焼鈍の前段の露点を４０〜６５℃とし、後段露点を４０〜７５℃とする方法などが知られている。しかしながらこれらの方法は、いずれも均質な被膜形成には一定の効果があるものと認められるとはいえ、必ずしも十分なものではなく、特に上述したように、鉄損低減のためにさらに被膜張力を増加させた際に十分な密着性が安定して得られないという問題がある。
【００１０】
また、脱炭焼鈍の昇温過程の制御により脱炭酸化現象を制御する方法として、例えば特許文献６には、脱炭焼鈍を施す前に、露点が０℃以下の雰囲気中で、６００〜６５０℃で３０秒以上１０分未満の事前焼鈍を行う方法が開示されている。しかしながらこの方法では、脱炭が不十分となる場合や、十分な密着性が安定して得られない場合がある。特許文献７には、２００〜７５０℃の温度域で、Ｐ_Ｈ２Ｏ／Ｐ_Ｈ２が０．３〜０．８５の雰囲気中で少なくとも８秒以上焼鈍処理を行う方法が開示されている。しかしながらこの方法では、十分な密着性が安定して得られない場合がある。
【００１１】
このように、上述の従来の方法では、仕上げ焼鈍被膜の品質や脱炭性に問題が生じる場合や、鉄損の低減のためさらに被膜張力を増加させた際の十分な密着性が安定して得られない場合があるなどの問題がある。
【００１２】
【特許文献１】
特開昭４８−３９３３８号公報
【特許文献２】
特開平６−３０６６２８号公報
【特許文献３】
特開昭５９−１８５７２５号公報
【特許文献４】
特開平２−２４０２１５号公報
【特許文献５】
特開平５−１４８５３２号公報
【特許文献６】
特開平２−７７５２６号公報
【特許文献７】
特開昭５９−３５６２４号公報
【００１３】
【発明が解決しようとする課題】
本発明は、上述の従来法の問題点を解決するものであって、絶縁性および張力付与性に優れた被膜を一方向性電磁鋼板の表面に形成することにより、優れた被膜密着性を有する低鉄損の一方向性電磁鋼板を得ることを目的とする。
【００１４】
【課題を解決するための手段】
本発明者らは、一方向性電磁鋼板の表面に張力付与性の被膜を形成するための脱炭焼鈍工程に関して、最適製造条件を見つけるべく鋭意検討を行った。
まず、脱炭焼鈍工程における昇温条件と仕上げ焼鈍被膜の密着性について調べたところ、８００℃での鋼板表面のＳｉ濃度と仕上げ焼鈍被膜の密着性との間には強い相関関係があり、前記Ｓｉ濃度が１５〜３０ｍｏｌ％の場合に、均質で密着性に優れた仕上げ焼鈍被膜が得られることを見出した。
【００１５】
この理由については明らかではないが、本発明者らは以下のように推定している。
脱炭焼鈍工程における内部酸化現象は、雰囲気中のＨ_２ＯおよびＯ_２がＯ原子として鋼板中へ溶解し、内方へ拡散することにより進行するため、鋼板表面に存在する酸化膜の相および形態が内部酸化現象に大きな影響を及ぼす。脱炭焼鈍における内部酸化現象は約８００℃から活発になるため、昇温過程において８００℃に達する時点の鋼板表面におけるＳｉの濃度が、それ以降に形成する内部酸化物の形態や分布に大きな影響を与えるものと考えられる。
【００１６】
なお、被膜の曲げ密着性は、仕上げ焼鈍被膜の形態と密接な関係があることが知られており、仕上げ焼鈍被膜と鋼板の界面が鋼板内部に食い込んだ形態をしていると、くさび止め効果などにより密着性が上昇する。本発明者らが見出した後述の上記条件下では、界面がこのような形態になっているものと考えられる。
【００１７】
さらに本発明者らは、脱炭焼鈍工程の昇温過程において８００℃に達する時点の鋼板表面におけるＳｉの濃度は、６００〜８００℃の温度域における平均昇温速度と雰囲気のＰ_Ｈ２Ｏ／Ｐ_Ｈ２比の組み合わせにより制御可能であることを見出した。すなわち、昇温過程の６００〜８００℃の温度域における平均昇温速度は、仕上げ焼鈍被膜の品質や密着性により１０〜１００℃／ｓに限定されるが、この平均昇温速度範囲において、雰囲気のＰ_Ｈ２Ｏ／Ｐ_Ｈ２比が０．０２〜０．２であれば、鋼板表面のＳｉ濃度が１５〜３０ｍｏｌ％となることを見出した。
【００１８】
本発明は上記知見に基づくものであり、その要旨とするところは以下の通りである。
（１）一方向性電磁鋼板の脱炭焼鈍工程において、昇温帯の８００℃での該鋼板表面のＳｉ濃度が１５〜３０ｍｏｌ％となる条件で処理を行うことを特徴とする一方向性電磁鋼板の絶縁被膜形成方法。
（２）前記脱炭焼鈍工程において、昇温帯の６００〜８００℃における平均昇温速度が１０〜１００℃／ｓで、かつ、Ｐ_Ｈ２Ｏ／Ｐ_Ｈ２比が０．０２〜０．２であることを特徴とする前記（１）記載の一方向性電磁鋼板の絶縁被膜形成方法。
【００１９】
【発明の実施の形態】
本発明に係る一方向性電磁鋼板の絶縁被膜形成方法は、脱炭焼鈍工程条件に特徴があり、従って脱炭焼鈍工程以外の、例えば熱間圧延、冷間圧延、窒化処理、焼鈍分離剤塗布工程、最終仕上げ焼鈍等の基本工程の条件については、特に限定はなく、本発明に係る絶縁性および張力付与性の優れた一方向性電磁鋼板が得られるものであれば構わない。
【００２０】
本発明に係る脱炭焼鈍工程について、以下に説明する。
脱炭焼鈍の均熱温度は、一次再結晶粒の大きさから、８００〜８７０℃の範囲が好ましく、他の焼鈍条件は板厚、鋼成分などに応じて選択する。
上述のように本発明においては、内部酸化現象が活発になる約８００℃に達する時点の鋼板表面におけるＳｉ濃度を１５〜３０ｍｏｌ％に制御することが重要であり、外部酸化現象が活発になる６００℃から内部酸化現象が活発になる８００℃の温度域における焼鈍条件を制御することが重要である。すなわち、鋼板中のＳｉの拡散速度の制約のため、昇温過程の約８００℃に達する時点で鋼板表面に形成する外部酸化膜の厚さは２０ｎｍ以下と非常に薄いが、この表面の外部酸化物が、均熱過程で生じる厚さ２〜５μｍの内部酸化層の形成を支配する。
【００２１】
８００℃に達する時点の鋼板表面におけるＳｉの濃度と、仕上げ焼鈍被膜の密着性との間には強い相関があり、そのＳｉ濃度が１５〜３０ｍｏｌ％である場合に、均質で密着性に優れる仕上げ焼鈍被膜が得られる。Ｓｉ濃度が１５ｍｏｌ％未満では、仕上げ焼鈍被膜の十分な密着性が得られない。一方、３０ｍｏｌ％超では、内部酸化現象および脱炭現象が阻害され十分な被膜密着性が得られない場合や、さらには、磁気特性から鋼中のＣ濃度を３０ｐｐｍ以下にすることが必須条件であるものの、３０ｐｐｍ以下にできない場合がある。
【００２２】
６００〜８００℃の温度範囲において制御すべき焼鈍条件としては、平均昇温速度および雰囲気のＰ_Ｈ２Ｏ／Ｐ_Ｈ２比が挙げられる。
６００〜８００℃の昇温帯における平均昇温速度は、１０〜１００℃／ｓが好ましい。平均昇温速度が１０℃／ｓ未満の場合は、昇温過程において内部酸化および脱炭が顕著に進行するため仕上げ焼鈍被膜の十分な密着性向上効果が得られず、一方、平均昇温速度が１００℃／ｓ超の場合は、鋼板全面にわたってＳｉＯ_２を主とする外部酸化物を均一に形成することが困難であるため、安定した品質および密着性を有する仕上げ焼鈍被膜を形成できない場合がある。さらに、６００〜８００℃の昇温帯における雰囲気のＰ_Ｈ２Ｏ／Ｐ_Ｈ２比は、８００℃における鋼板表面のＳｉ濃度を１５〜３０ｍｏｌ％とするために０．０２〜０．２の範囲に限定する。
【００２３】
本発明に係る脱炭焼鈍工程において鋼板表面に形成するＳｉＯ_２主体の外部酸化物層は、厚さが数〜数１０ｎｍと極めて薄いため、このＳｉＯ_２主体の外部酸化物層の組成および膜厚の分析は、Ｘ線光電子分光法（ＸＰＳ）やオージェ電子分光法（ＡＥＳ）が好適に用いられる。ＸＰＳやＡＥＳにより表面のＳｉ濃度を分析する場合、０．０１〜１ｍｍ^２の領域の面分析を行い、表面のＳｉ濃度を求める。ここで、鋼板表面における外部酸化物の分布は微視的には不均一であるため、分析面積が０．０１ｍｍ^２未満の場合は測定結果が測定場所により大きくばらつき、また１ｍｍ^２以上の領域を一度に測定するのは一般的なＸＰＳおよびＡＥＳ装置の性能上困難であるため、分析領域の面積は０．０１〜１ｍｍ^２が望ましい。
【００２４】
なお、８００℃に達する時点の鋼板表面におけるＳｉの濃度を分析する場合は、例えば本発明に係る脱炭焼鈍条件下（６００〜８００℃における昇温速度：１０〜１００℃／ｓ、Ｐ_Ｈ２Ｏ／Ｐ_Ｈ２：０．０２〜０．２）で鋼板を８００℃まで加熱し、８００℃に到達後、直ちに３０℃／ｓ以上の冷却速度で４００℃まで昇温時と同一雰囲気中において冷却し、同雰囲気中で室温まで冷却後に鋼板試料をＸＰＳやＡＥＳにより分析すればよい。
【００２５】
冷却過程において８００℃での表面状態を維持するには、冷却速度が重要であり、その上限は特に限定はないが、下限は３０℃／ｓ以上の冷却速度が必要であり、好ましくは１００℃／ｓ以上の速度で冷却する。ここで、炉温が室温になるまで３０℃／ｓ以上の冷却速度で冷却することが望ましいが、外部酸化速度が非常に遅くなる４００℃まで３０℃／ｓ以上の冷却速度で冷却することにより８００℃での表面状態を維持することができる。
【００２６】
次に、上記脱炭焼鈍に引き続いて行う窒化焼鈍工程の後に、ＭｇＯを主成分とする焼鈍分離剤を塗布し、水素雰囲気中で約１０００〜１２００℃で約５〜５０ｈ加熱する仕上げ焼鈍工程を行い、鋼板表面にフォルステライト主体の被膜（仕上げ焼鈍被膜）を形成する。仕上げ焼鈍被膜は、上述のように、脱炭焼鈍工程で生ずるＳｉＯ_２主体の酸化膜と、焼鈍分離剤として通常用いられるＭｇＯとが、仕上げ焼鈍中に反応して形成するものである。
【００２７】
本発明は、優れた密着性を有する仕上げ焼鈍被膜を形成するものであり、張力付与型の絶縁被膜を仕上げ焼鈍被膜の上に形成した場合に好適に効果を発揮する。本発明に係る張力付与型の絶縁被膜の形成方法としては、通常の方法を用いることができ、脱炭焼鈍処理を行った後の鋼板表面に絶縁被膜材質を塗布・焼き付ければよい。
【００２８】
本発明に係る張力付与型の絶縁被膜としては、一方向性電磁鋼板に通常使用される耐熱性の無機絶縁被膜が適用できる。具体的には、特許文献１に開示されているようなコロイド状シリカと燐酸塩を主体とするコーティング液を塗布焼き付けることによって得られる絶縁被膜や、特許文献２に開示されているようなアルミナゾルと硼酸を主体とするコーティング液を塗布焼き付けることによって得られるＡ１_２Ｏ_３−Ｂ_２Ｏ_３系の結晶質被膜が挙げられる。また、特開平６−２４８４６５号公報には各種の張力被膜材質が開示されているが、この中のアルミナ被膜は、アルミナゾルを塗布・焼き付けることによって得られる。
本発明に係る被膜形成方法によって、電磁鋼板と絶縁被膜の間の密着性が向上し、強い張力が付与された一方向性電磁鋼板が製造可能となる。
【００２９】
【実施例】
次に、実施例によって本発明の作用効果をさらに具体的に説明するが、本発明はこれらの実施例に限定されるものではない。
（実施例１）
質量％で、Ｓｉ：３．２％、Ｃ：０．０５％、酸可溶性Ａｌ：０．０３％、Ｎ：０．００７％、Ｍｎ：０．１％、Ｓ：０．００７％、Ｃｒ：０．１％、Ｓｎ：０．０５％、残部がＦｅと不可避的不純物からなるスラブを１１５０℃に加熱し、熱間圧延により板厚を２．０ｍｍにした後、１１２０℃で焼鈍、酸洗後、冷間圧延により最終板厚を０．２３ｍｍとした冷延板を複数枚作製した。
【００３０】
次に、これらの冷延板に対して、雰囲気露点を変化させることで昇温帯のＰ_Ｈ２Ｏ／Ｐ_Ｈ２比を変え（実施例１−１：Ｐ_Ｈ２Ｏ／Ｐ_Ｈ２比＝０．０３、実施例１−２：Ｐ_Ｈ２Ｏ／Ｐ_Ｈ２比＝０．１０、実施例１−３：Ｐ_Ｈ２Ｏ／Ｐ_Ｈ２比＝０．１５）、昇温速度は３０℃／ｓとして、８３０℃まで加熱した。続いて脱炭処理は、８３０℃でＰ_Ｈ２Ｏ／Ｐ_Ｈ２比が０．４４の雰囲気中で１２０秒間の焼鈍を行った。
なお、８００℃に達した時点の鋼板表面のＳｉ濃度の分析は、前記条件で加熱を行い、加熱温度が８００℃に到達した後、直ちに１００℃／ｓの冷却速度で室温まで冷却した試料を作製し、Ｘ線光電子分光法（ＸＰＳ）によって分析を行った。
【００３１】
その後、アンモニア含有雰囲気中で７５０℃で３０秒間窒化焼鈍し、鋼板中の全窒素量を０．０２質量％とした。次いでＭｇＯを主成分とする焼鈍分離剤を表面に塗布した後、１２００℃で２０時間仕上げ焼鈍を施した。
次いで未反応焼鈍分離剤を除去した後、特許文献１に開示されている方法に準拠して、コロイド状シリカ、燐酸アルミニウム、無水クロム酸からなる処理液を表面に塗布し、８５０℃で焼き付けることにより、張力付与型の絶縁被膜を形成した（絶縁被膜形成量：片面当たり１２ｇ／ｍ^２）。
【００３２】
絶縁被膜の密着性は、直径１５ｍｍおよび２０ｍｍの丸棒に対して、角度が１８０度になるように鋼板を巻き付けた際の、被膜の剥離した面積率により評価した。２０ｍｍφの丸棒に巻き付けた際の剥離面積率が０％の場合を密着性良好とする。
【００３３】
表１に結果を示す。本発明法により形成した絶縁被膜（実施例１−１〜１−３）は、８００℃到達時の鋼板表面のＳｉ濃度が１７〜２５ｍｏｌ％であり、さらに、２０ｍｍφの丸棒に巻き付けた際の剥離面積率が０％であり、密着性良好であった。
【００３４】
【表１】

【００３５】
（比較例１）
実施例１と同様の成分および条件で冷延板を複数枚作製した。
次に、これらの冷延板に対して、雰囲気露点を変化させることで昇温帯のＰ_Ｈ２Ｏ／Ｐ_Ｈ２比を変え（比較例１−１：０．００８、比較例１−２：０．４４）、昇温速度は３０℃／ｓとして、８３０℃まで加熱し、続く脱炭処理は実施例１と同一の条件下で行った。なお、８００℃に達する時点の鋼板表面のＳｉ濃度の分析は、実施例１と同様の方法および条件によって行った。
【００３６】
その後、実施例１と同様の条件で窒化焼鈍、仕上げ焼鈍を行い、鋼板表面に絶縁被膜を形成し、実施例１と同様の方法で絶縁被膜の密着性の評価を行った。
表１に結果を示す。本発明法の範囲外の絶縁被膜（比較例１−１、１−２）は、８００℃到達時の鋼板表面のＳｉ濃度が１５〜３０ｍｏｌ％の範囲外であり、さらに、２０ｍｍφの丸棒に巻き付けた際の剥離面積率がそれぞれ２０％、４０％となり密着性が不良であった。
【００３７】
実施例１および比較例１の結果から、脱炭焼鈍工程の昇温過程の８００℃に達する時点の鋼板表面におけるＳｉ濃度が１５〜３０ｍｏｌ％場合に、被膜の密着性が良好となる仕上げ焼鈍被膜を形成できることがわかる。
【００３８】
（実施例２）
実施例１と同様の成分および条件で冷延板を複数枚作製した。
次に、これらの冷延板に対して、それぞれ異なる昇温速度で脱炭焼鈍処理を行った。昇温帯における雰囲気のＰ_Ｈ２Ｏ／Ｐ_Ｈ２比は０．１０とし、昇温速度を変えて（実施例２−１：１５℃／ｓ、実施例２−２：４０℃／ｓ、実施例２−３：１００℃／ｓ）８３０℃まで昇温後、続いて８３０℃でＰ_Ｈ２Ｏ／Ｐ_Ｈ２比が０．４４の雰囲気中で１２０秒間の均熱脱炭処理を行った。なお、８００℃に達する時点の鋼板表面のＳｉ濃度の分析は、実施例１と同様の方法および条件によって行った。
【００３９】
その後、実施例１と同様の条件で窒化焼鈍、仕上げ焼鈍を行い、鋼板表面に絶縁被膜を形成し、実施例１と同様の方法で絶縁被膜の密着性の評価を行った。
表２に結果を示す。本発明法により形成した絶縁被膜（実施例２−１〜２−３）は、８００℃到達時の鋼板表面のＳｉ濃度が１８〜２１ｍｏｌ％であり、さらに、２０ｍｍφの丸棒に巻き付けた際の剥離面積率が０％であり、密着性良好であった。
【００４０】
【表２】

【００４１】
（比較例２）
実施例１と同様の成分および条件で冷延板を複数枚作製した。
次に、これらの冷延板に対して、それぞれ異なる昇温速度で脱炭焼鈍処理を行った。昇温帯における雰囲気のＰ_Ｈ２Ｏ／Ｐ_Ｈ２比は０．１０とし、昇温速度を変えて（比較例２−１：５℃／ｓ、比較例２−２：１５０℃／ｓ）８３０℃まで昇温後、続く均熱脱炭処理は実施例２と同一の条件下で行った。なお、８００℃に達する時点の鋼板表面のＳｉ濃度の分析は、実施例１と同様の方法および条件によって行った。
【００４２】
その後、実施例１と同様の条件で窒化焼鈍、仕上げ焼鈍を行い、鋼板表面に絶縁被膜を形成し、実施例１と同様の方法で絶縁被膜の密着性の評価を行った。
表２に結果を示す。本発明法の範囲外の絶縁被膜（比較例２−１、２−２）は、８００℃到達時の鋼板表面のＳｉ濃度が１５〜３０ｍｏｌ％の範囲外であり、さらに、２０ｍｍφの丸棒に巻き付けた際の剥離面積率がそれぞれ３０％、１０％となり密着性が不良であった。
【００４３】
実施例２および比較例２の結果から、脱炭焼鈍工程の昇温過程の８００℃に達する時点の鋼板表面におけるＳｉ濃度が１５〜３０ｍｏｌ％場合に、被膜の密着性が良好となる仕上げ焼鈍被膜を形成できることがわかる。
【００４４】
【発明の効果】
本発明により、電磁鋼板と絶縁被膜の間の密着性の改善が可能であり、本発明の絶縁被膜形成法により、強い張力が付与された一方向性電磁鋼板が製造でき、その工業的効果は極めて大きい。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for forming a coating having excellent insulating properties and tension imparting properties on the surface of a grain-oriented electrical steel sheet.
[0002]
[Prior art]
The grain-oriented electrical steel sheet has a crystal structure having a main orientation of (110) [001] and is frequently used as a magnetic core material. In order to reduce energy loss, a material with small iron loss is required. . In particular, in order to reduce iron loss of a grain-oriented electrical steel sheet containing 5% by mass or less of silicon, it is effective to apply a tension to the steel sheet. By applying a tension up to about 15 MPa, the iron loss can be effectively reduced. It is known that it can be reduced.
[0003]
Normally, the tension is applied by a film formed on the surface of the steel sheet. Therefore, it is effective to apply a tension to the surface of the steel sheet at a high temperature for applying the tension. This utilizes the thermal stress caused by the difference in thermal expansion coefficient between the steel sheet and the coating.
[0004]
An oxide film mainly composed of SiO ₂ generated in a decarburizing annealing step and MgO usually used as an annealing separator are formed on the surface of a normal grain-oriented electrical steel sheet by reacting during final annealing. There is a stellite-based coating (hereinafter referred to as a finish-annealed coating). A general method of forming an insulating film on the surface of a grain-oriented electrical steel sheet is to apply an insulating film after leaving a finish-annealed film. The finish annealed film has a large tension applied to the steel sheet, and is effective in reducing iron loss.
[0005]
The finish-annealed coating is required to be uniform and free from defects, and to have excellent adhesion that can withstand shearing, punching, bending and the like. Patent Document 1 discloses a finish-annealed film obtained by applying and baking a coating liquid mainly composed of colloidal silica and phosphate to the surface of a steel sheet, and this coating has an effect of imparting tension to the steel sheet. Is large, indicating that it is effective in reducing iron loss.
[0006]
In addition, attempts have been made to increase the tension on a steel sheet by forming an insulating film on the steel sheet. For example, Patent Document _{_{_{2, A1 2 O 3 -B 2}}} O 3 based crystalline coating obtained by baking a coating solution mainly containing alumina sol and boric acid on the steel sheet is disclosed. The insulating film may have a film tension 1.5 to 2 times that of the final annealed film formed by baking a coating mainly composed of colloidal silica and phosphate under the same film thickness. Has been described.
[0007]
In general, insulating coatings can provide considerable coating adhesion when formed on a finish-annealed coating, but if the coating tension is further increased to reduce iron loss, the adhesion will be insufficient. It is necessary to form a finish-annealed film having excellent adhesion.
[0008]
As described above, since the finish-annealed film is made of an oxide mainly composed of SiO ₂ generated in the decarburizing annealing step as one of the raw materials, the type, amount, distribution, and the like of this oxide depend on the mechanical strength of the finish-annealed film and the steel sheet. Affects adhesion. Therefore, control of the decarburizing annealing step is extremely important for forming a good finish annealing film.
[0009]
Regarding the decarburizing annealing of the grain-oriented electrical steel sheet, for example, a method of controlling the dew point of the annealing atmosphere to 50 to 70 ° C. as disclosed in Patent Document 3 and a decarburizing annealing as disclosed in Patent Document 4 A method of performing a heat treatment in a non-oxidizing atmosphere later, a method of setting the dew point of the first stage of decarburizing annealing to 40 to 65 ° C. and setting the dew point of the second stage to 40 to 75 ° C. as disclosed in Patent Document 5 are known. ing. However, although all of these methods are recognized to have a certain effect in forming a uniform film, they are not always sufficient, and as described above, the film tension is further increased in order to reduce iron loss. There is a problem that sufficient adhesion cannot be stably obtained when the amount is increased.
[0010]
As a method of controlling the decarboxylation phenomenon by controlling the temperature rise process of decarburization annealing, for example, Patent Document 6 discloses that before decarburization annealing, before decarburization annealing, the dew point is set to 600 to 650 in an atmosphere having a dew point of 0 ° C. or less. A method of performing pre-annealing at 30 ° C. for at least 30 seconds and less than 10 minutes is disclosed. However, in this method, decarburization may be insufficient or sufficient adhesion may not be stably obtained. Patent Literature 7 discloses a method of performing an annealing treatment in a temperature range of 200 to 750 ° C. in an atmosphere of P _H2O / P _H2 of 0.3 to 0.85 for at least 8 seconds or more. However, in this method, sufficient adhesion may not be obtained stably.
[0011]
As described above, in the above-described conventional method, when there is a problem in the quality and decarburization property of the finish-annealed coating, and sufficient adhesion when the coating tension is further increased to reduce iron loss is stable. There are problems such as not being able to be obtained.
[0012]
[Patent Document 1]
JP-A-48-39338 [Patent Document 2]
JP-A-6-306628 [Patent Document 3]
JP-A-59-185725 [Patent Document 4]
JP-A-2-240215 [Patent Document 5]
JP-A-5-148532 [Patent Document 6]
JP-A-2-77526 [Patent Document 7]
JP-A-59-35624
[Problems to be solved by the invention]
The present invention solves the problems of the above-mentioned conventional method, and has excellent coating adhesion by forming a coating excellent in insulation and tension imparting properties on the surface of a grain-oriented electrical steel sheet. It aims to obtain a unidirectional electrical steel sheet with low iron loss.
[0014]
[Means for Solving the Problems]
The present inventors have conducted intensive studies on the decarburizing annealing step for forming a tension-imparting film on the surface of a grain-oriented electrical steel sheet in order to find optimal manufacturing conditions.
First, the temperature rise conditions in the decarburizing annealing step and the adhesion of the finish annealing film were examined, and there was a strong correlation between the Si concentration on the steel sheet surface at 800 ° C. and the adhesion of the finish annealing film. It has been found that when the Si concentration is 15 to 30 mol%, a finish-annealed film having a uniform and excellent adhesion can be obtained.
[0015]
Although the reason is not clear, the present inventors presume as follows.
The internal oxidation phenomenon in the decarburizing annealing process proceeds by H ₂ O and O ₂ in the atmosphere being dissolved as O atoms in the steel sheet and diffusing inward, so that the phase of the oxide film existing on the steel sheet surface and Morphology greatly affects internal oxidation. Since the internal oxidation phenomenon during decarburization annealing becomes active from about 800 ° C, the concentration of Si on the steel sheet surface at the time when the temperature reaches 800 ° C in the temperature rise process has a large effect on the form and distribution of internal oxides formed thereafter. It is thought to give.
[0016]
It is known that the bending adhesion of the coating has a close relationship with the form of the finish-annealed coating. Adhesion increases due to such factors. It is considered that the interface is in such a form under the above-described conditions found by the present inventors described below.
[0017]
Furthermore, the present inventors have found that the concentration of Si on the steel sheet surface at the time of reaching 800 ° C. in the temperature rising process of the decarburizing annealing step is determined by the average temperature rising rate in the temperature range of 600 to 800 ° C. and the PH _{2 O} / P _H2 It has been found that control is possible by a combination of ratios. That is, the average heating rate in the temperature range of 600 to 800 ° C. in the heating process is limited to 10 to 100 ° C./s depending on the quality and adhesion of the finish-annealed film. It was found that when the P _H2O / P _H2 ratio of the steel sheet was 0.02 to 0.2, the Si concentration on the steel sheet surface was 15 to 30 mol%.
[0018]
The present invention is based on the above findings, and the gist is as follows.
(1) In the decarburizing annealing step of a unidirectional magnetic steel sheet, the treatment is performed under the condition that the Si concentration on the surface of the steel sheet at 800 ° C. in the temperature rising zone is 15 to 30 mol%. Method for forming an insulating film.
(2) In the decarburizing annealing step, the average heating rate at 600 to 800 ° C. in the heating zone is 10 to 100 ° C./s, and the P _H2O / P _H2 ratio is 0.02 to 0.2. The method for forming an insulating film on a grain-oriented electrical steel sheet according to the above (1), characterized in that:
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
The method for forming an insulating coating on a grain-oriented electrical steel sheet according to the present invention is characterized by the conditions of the decarburizing annealing step, and therefore, other than the decarburizing annealing step, for example, hot rolling, cold rolling, nitriding treatment, application of an annealing separator. The conditions of the basic steps such as the step and the final finish annealing are not particularly limited, and any conditions may be used as long as the grain-oriented electrical steel sheet according to the present invention having excellent insulating properties and tension imparting properties can be obtained.
[0020]
The decarburizing annealing step according to the present invention will be described below.
The soaking temperature for decarburization annealing is preferably in the range of 800 to 870 ° C. in view of the size of the primary recrystallized grains, and other annealing conditions are selected according to the sheet thickness, steel composition, and the like.
As described above, in the present invention, it is important to control the Si concentration at the surface of the steel sheet to 15 to 30 mol% when the internal oxidation phenomenon becomes active at about 800 ° C., and the external oxidation phenomenon becomes active 600 It is important to control the annealing conditions in the temperature range of 800 ° C. where the internal oxidation phenomenon becomes active from the temperature of ° C. That is, due to the restriction of the diffusion rate of Si in the steel sheet, the thickness of the external oxide film formed on the steel sheet surface at the time when the temperature reaches about 800 ° C. in the temperature rising process is extremely thin, 20 nm or less. The substance governs the formation of an internal oxide layer having a thickness of 2 to 5 μm which occurs during the soaking process.
[0021]
There is a strong correlation between the concentration of Si on the steel sheet surface at the time of reaching 800 ° C. and the adhesion of the finish-annealed film. When the Si concentration is 15 to 30 mol%, the finish is uniform and excellent in adhesion. An annealed coating is obtained. If the Si concentration is less than 15 mol%, sufficient adhesion of the finish-annealed film cannot be obtained. On the other hand, if it exceeds 30 mol%, the internal oxidation phenomenon and the decarburization phenomenon are inhibited, and sufficient film adhesion cannot be obtained. Further, it is an essential condition that the C concentration in the steel is set to 30 ppm or less from the magnetic properties. In some cases, however, it may not be possible to reduce the concentration to 30 ppm or less.
[0022]
Annealing conditions to be controlled in the temperature range of 600 to 800 ° C. include an average heating rate and a P _H2O / P _H2 ratio of the atmosphere.
The average heating rate in the heating zone of 600 to 800 ° C is preferably 10 to 100 ° C / s. If the average heating rate is less than 10 ° C./s, the internal oxidation and decarburization remarkably progress in the heating process, so that a sufficient effect of improving the adhesion of the finish-annealed film cannot be obtained. Is more than 100 ° C./s, it is difficult to uniformly form an external oxide mainly composed of SiO ₂ over the entire surface of the steel sheet, so that a finish-annealed film having stable quality and adhesion may not be formed. is there. Further, the P _H2O / P _H2 ratio of the atmosphere in the temperature rise zone of 600 to 800 ° C. is limited to the range of 0.02 to 0.2 in order to set the Si concentration on the steel sheet surface at 800 ° C. to 15 to 30 mol%.
[0023]
SiO ₂ mainly outer oxide layer which forms on the surface of the steel sheet in the decarburization annealing step according to the present invention, since the extremely thin as several to several 10nm thickness, composition and thickness of the outer oxide layer of the SiO ₂ mainly The analysis of X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) are suitably used for the analysis. When analyzing the Si concentration on the surface by XPS or AES, a surface analysis of a region of 0.01 to ¹ mm ² is performed to determine the Si concentration on the surface. Here, the distribution of external oxides on the surface of the steel sheet is microscopically non-uniform, so that when the analysis area is less than 0.01 mm ² , the measurement results vary widely depending on the measurement location, and the area of 1 mm ² or more Since it is difficult to perform the measurement at one time due to the performance of general XPS and AES devices, the area of the analysis region is preferably 0.01 to ¹ mm ² .
[0024]
When analyzing the concentration of Si on the steel sheet surface at the time when the temperature reaches 800 ° C, for example, the conditions of decarburization annealing according to the present invention (heating rate at 600 to 800 ° C: 10 to 100 ° C / s, PH _{2 O} / (P _H2 : 0.02 to 0.2), the steel sheet is heated to 800 ° C., and after reaching 800 ° C., immediately cooled to 400 ° C. at a cooling rate of 30 ° C./s or more in the same atmosphere as when the temperature was raised, After cooling to room temperature in the same atmosphere, the steel sheet sample may be analyzed by XPS or AES.
[0025]
In order to maintain the surface state at 800 ° C. during the cooling process, the cooling rate is important, and the upper limit is not particularly limited, but the lower limit requires a cooling rate of 30 ° C./s or more, preferably 100 ° C. Cool at a rate of / s or more. Here, it is desirable to cool at a cooling rate of 30 ° C./s or more until the furnace temperature becomes room temperature, but by cooling at a cooling rate of 30 ° C./s or more to 400 ° C. where the external oxidation rate becomes very slow. The surface state at 800 ° C. can be maintained.
[0026]
Next, after the nitriding annealing step performed subsequent to the decarburizing annealing, a finishing annealing step of applying an annealing separating agent containing MgO as a main component and heating at about 1000 to 1200 ° C. for about 5 to 50 hours in a hydrogen atmosphere is performed. Then, a forsterite-based coating (final annealing coating) is formed on the steel sheet surface. As described above, the finish annealing film is formed by the reaction between the oxide film mainly composed of SiO ₂ generated in the decarburizing annealing step and MgO usually used as an annealing separator during the finish annealing.
[0027]
INDUSTRIAL APPLICABILITY The present invention is to form a finish-annealed film having excellent adhesion, and exhibits a suitable effect when a tension-imparting insulating film is formed on the finish-annealed film. As a method of forming the tension-imparting insulating film according to the present invention, an ordinary method can be used, and the material of the insulating film may be applied and baked on the steel sheet surface after the decarburizing annealing treatment.
[0028]
As the tension-imparting insulating film according to the present invention, a heat-resistant inorganic insulating film usually used for a grain-oriented electrical steel sheet can be applied. Specifically, an insulating film obtained by applying and baking a coating solution mainly composed of colloidal silica and a phosphate as disclosed in Patent Document 1 or an alumina sol as disclosed in Patent Document 2 include _A1 2 _{_O 3} _-B 2 _O 3 based crystalline coating obtained by baking coating a coating liquid mainly composed of boric acid. Japanese Patent Application Laid-Open No. 6-248465 discloses various types of tension coating materials, and the alumina coating among them is obtained by applying and baking alumina sol.
ADVANTAGE OF THE INVENTION By the film formation method which concerns on this invention, the adhesiveness between an electrical steel sheet and an insulating coating improves, and it becomes possible to manufacture the unidirectional electrical steel sheet to which strong tension was given.
[0029]
【Example】
Next, the operation and effect of the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.
(Example 1)
In mass%, Si: 3.2%, C: 0.05%, acid-soluble Al: 0.03%, N: 0.007%, Mn: 0.1%, S: 0.007%, Cr: A slab consisting of 0.1%, Sn: 0.05%, and the balance of Fe and unavoidable impurities is heated to 1150 ° C, and hot-rolled to a thickness of 2.0 mm, then annealed at 1120 ° C and pickled. Thereafter, a plurality of cold-rolled sheets having a final thickness of 0.23 mm were produced by cold rolling.
[0030]
Next, with respect to these cold rolled sheets, the P _H2O / P _H2 ratio in the heating zone was changed by changing the atmosphere dew point (Example 1-1: P _H2O / P _H2 ratio = 0.03, Example 1-2: P _H2O / P _H2 ratio = 0.10, Example 1-3: P _H2O / P _H2 ratio = 0.15), and heating was performed to 830 ° C. at a heating rate of 30 ° C./s. Subsequently, in the decarburization treatment, annealing was performed at 830 ° C. in an atmosphere having a P _H2O / P _H2 ratio of 0.44 for 120 seconds.
The analysis of the Si concentration on the steel sheet surface at the time when the temperature reached 800 ° C. was performed by heating under the above conditions, and immediately after the heating temperature reached 800 ° C., was cooled to room temperature at a cooling rate of 100 ° C./s. It was fabricated and analyzed by X-ray photoelectron spectroscopy (XPS).
[0031]
Thereafter, nitriding annealing was performed at 750 ° C. for 30 seconds in an atmosphere containing ammonia to reduce the total nitrogen content in the steel sheet to 0.02% by mass. Next, after applying an annealing separator containing MgO as a main component to the surface, finish annealing was performed at 1200 ° C. for 20 hours.
Then, after removing the unreacted annealing separating agent, a treatment liquid comprising colloidal silica, aluminum phosphate, and chromic anhydride is applied to the surface in accordance with the method disclosed in Patent Document 1, and baked at 850 ° C. As a result, a tension-imparting insulating film was formed (the amount of the insulating film formed: 12 g / m ² per side).
[0032]
The adhesion of the insulating coating was evaluated based on the area ratio of the peeled coating when a steel plate was wound around a round bar having a diameter of 15 mm or 20 mm at an angle of 180 degrees. A case where the peeling area ratio when wound around a 20 mmφ round bar is 0% is regarded as good adhesion.
[0033]
Table 1 shows the results. The insulating film formed by the method of the present invention (Examples 1-1 to 1-3) had a Si concentration of 17 to 25 mol% on the steel sheet surface when the temperature reached 800 ° C., and was further wound around a 20 mmφ round bar. The peeling area ratio was 0%, and the adhesion was good.
[0034]
[Table 1]

[0035]
(Comparative Example 1)
A plurality of cold-rolled sheets were produced under the same components and conditions as in Example 1.
Next, for these cold-rolled sheets, the P _H2O / P _H2 ratio in the heating zone was changed by changing the atmosphere dew point (Comparative Example 1-1: 0.008, Comparative Example 1-2: 0.44). ), The temperature was raised to 830 ° C. at a rate of 30 ° C./s, and the subsequent decarburization treatment was performed under the same conditions as in Example 1. The analysis of the Si concentration on the surface of the steel sheet when the temperature reached 800 ° C. was performed by the same method and under the same conditions as in Example 1.
[0036]
Thereafter, nitriding annealing and finish annealing were performed under the same conditions as in Example 1, an insulating film was formed on the steel sheet surface, and the adhesion of the insulating film was evaluated in the same manner as in Example 1.
Table 1 shows the results. Insulation coatings (comparative examples 1-1 and 1-2) out of the range of the method of the present invention have an Si concentration on the steel sheet surface at 800 ° C. outside the range of 15 to 30 mol%, and are further converted into a round bar of 20 mmφ. The peeled area ratios when wound were 20% and 40%, respectively, and the adhesion was poor.
[0037]
From the results of Example 1 and Comparative Example 1, when the Si concentration on the steel sheet surface at the time of reaching 800 ° C. in the temperature rising process of the decarburizing annealing step is 15 to 30 mol%, the finish annealing film having good adhesion of the film is obtained. It can be seen that can be formed.
[0038]
(Example 2)
A plurality of cold-rolled sheets were produced under the same components and conditions as in Example 1.
Next, decarburization annealing was performed on these cold-rolled sheets at different heating rates. The P _H2O / P _H2 ratio of the atmosphere in the heating zone was set to 0.10, and the heating rate was changed (Example 2-1: 15 ° C./s, Example 2-2: 40 ° C./s, Example 2- (3: 100 ° C./s) After the temperature was raised to 830 ° C., a soaking decarburization treatment was performed at 830 ° C. for 120 seconds in an atmosphere having a P _H2O / P _H2 ratio of 0.44. The analysis of the Si concentration on the surface of the steel sheet when the temperature reached 800 ° C. was performed by the same method and under the same conditions as in Example 1.
[0039]
Thereafter, nitriding annealing and finish annealing were performed under the same conditions as in Example 1, an insulating film was formed on the steel sheet surface, and the adhesion of the insulating film was evaluated in the same manner as in Example 1.
Table 2 shows the results. The insulating film formed by the method of the present invention (Examples 2-1 to 2-3) had a Si concentration of 18 to 21 mol% on the surface of the steel sheet when the temperature reached 800 ° C, and was further wound around a 20 mmφ round bar. The peeling area ratio was 0%, and the adhesion was good.
[0040]
[Table 2]

[0041]
(Comparative Example 2)
A plurality of cold-rolled sheets were produced under the same components and conditions as in Example 1.
Next, decarburization annealing was performed on these cold-rolled sheets at different heating rates. The P _H2O / P _H2 ratio of the atmosphere in the heating zone was set to 0.10, and the heating rate was changed (Comparative Example 2-1: 5 ° C./s, Comparative Example 2-2: 150 ° C./s) to rise to 830 ° C. After the heating, the subsequent soaking decarburization treatment was performed under the same conditions as in Example 2. The analysis of the Si concentration on the surface of the steel sheet when the temperature reached 800 ° C. was performed by the same method and under the same conditions as in Example 1.
[0042]
Thereafter, nitriding annealing and finish annealing were performed under the same conditions as in Example 1, an insulating film was formed on the steel sheet surface, and the adhesion of the insulating film was evaluated in the same manner as in Example 1.
Table 2 shows the results. Insulating coatings (comparative examples 2-1 and 2-2) out of the range of the method of the present invention have an Si concentration on the steel sheet surface at 800 ° C. outside the range of 15 to 30 mol%, and are further converted into a 20 mmφ round bar. The peeled area ratios when wound were 30% and 10%, respectively, and the adhesion was poor.
[0043]
The results of Example 2 and Comparative Example 2 show that when the Si concentration on the steel sheet surface at the time of reaching 800 ° C. in the temperature rising process of the decarburizing annealing step is 15 to 30 mol%, the finish annealing film having good adhesion of the film is obtained. It can be seen that can be formed.
[0044]
【The invention's effect】
According to the present invention, it is possible to improve the adhesion between the electrical steel sheet and the insulating coating, and by the insulating coating forming method of the present invention, it is possible to produce a unidirectional electrical steel sheet to which a strong tension is applied. Extremely large.

Claims

In the decarburizing annealing step of the unidirectional magnetic steel sheet, the treatment is performed under the condition that the Si concentration on the surface of the steel sheet at 800 ° C. in the heating zone is 15 to 30 mol%. Forming method.

In the decarburizing annealing step, the average heating rate at 600 to 800 ° C. in the heating zone is 10 to 100 ° C./s, and the P _H2O / P _H2 ratio is 0.02 to 0.2. The method for forming an insulating coating on a grain-oriented electrical steel sheet according to claim 1.