JP4456317B2

JP4456317B2 - Method for producing grain-oriented electrical steel sheet

Info

Publication number: JP4456317B2
Application number: JP2002053688A
Authority: JP
Inventors: 修一中村; 義行牛神; 健一村上
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 2001-04-16
Filing date: 2002-02-28
Publication date: 2010-04-28
Anticipated expiration: 2022-02-28
Also published as: JP2003003215A

Description

【０００１】
【発明の属する技術分野】
本発明は、結晶粒がミラー指数で｛１１０｝＜００１＞方位に集積した、いわゆる方向性電磁鋼板の製造方法に関するものである。この鋼板は、軟磁性材料として変圧器等の電気機器の鉄芯として用いられる。
【０００２】
【従来の技術】
方向性電磁鋼板は、｛１１０｝＜００１＞方位（いわゆるゴス方位）に集積した結晶粒により構成されたＳｉを４．８％以下含有した鋼板である。この鋼板は磁気特性として励磁特性と鉄損得性が要求される。励磁特性を表す指標としては磁場の強さ８００Ａ／ｍにおける磁束密度：Ｂ８が通常使用される。また、鉄損特性を表す指標としては周波数５０Ｈｚで１．７Ｔまで磁化した時の鋼板１ｋｇあたりの鉄損：Ｗ17/50が用いられる。磁束密度：Ｂ８は鉄損特性の最大の支配因子であり、磁束密度：Ｂ８値が高いほど鉄損特性も良好になる。磁束密度：Ｂ８を高めるためには結晶方位を高度に揃えることが重要である。この結晶方位の制御は二次再結晶とよばれるカタストロフィックな粒成長現象を利用して達成される。
【０００３】
この二次再結晶を制御するためには、二次再結晶前の一次再結晶組織の調整と、インヒビタ−とよばれる微細析出物の調整を行うことが必要である。このインヒビタ−は、一次再結晶組織のなかで一般の粒の成長を抑制し、特定の｛１１０｝＜００１＞方位粒のみを優先成長させる機能を持つ。
析出物として代表的なものとしては、Ｍ．Ｆ．Ｌｉｔｔｍａｎｎ（特公昭３０−３６５１号公報）及びＪ．Ｅ．Ｍａｙ＆Ｄ．Ｔｕｒｎｂｕｌｌ（Ｔｒａｎｓ．Ｍｅｔ．Ｓｏｃ．ＡＩＭＥ２１２（１９５８年）ｐ７６９）等はＭｎＳを、田口ら（特公昭４０−１５６４４号公報）はＡｌＮを、今中ら（特公昭５１−１３４６９号公報）はＭｎＳｅを提示している。
【０００４】
これらの析出物は熱間圧延前のスラブ加熱時に完全固溶させた後に、熱間圧延及びその後の焼鈍工程で微細析出させる方法がとられている。これらの析出物を完全固溶させるためには１３５０℃ないし１４００℃以上の高温で加熱する必要があり、これは普通鋼のスラブ加熱温度に比べて約２００℃高く次の問題点がある。（１）専用の加熱炉が必要。（２）加熱炉のエネルギ−原単位が高い。（３）溶融スケール量が多く、いわゆるノロ出し等の操業管理が必要である。
【０００５】
そこで低温スラブ加熱による研究開発が進められ、低温スラブ加熱による製造方法として小松ら（特公昭６２−４５２８５号公報）は窒化処理により形成した（Ａｌ，Ｓｉ）Ｎをインヒビターとして用いる方法を開示している。この窒化処理の方法として、小林等は脱炭焼鈍後にストリップ状で窒化する方法を開示（特開平２-７７５２５号公報）し、牛神等によりその窒化物の挙動が報告されている（Materials Science Forum, 204-206 (1996),pp593-598）。
【０００６】
低温スラブ加熱による方向性電磁鋼板の製造方法においては、脱炭焼鈍時にインヒビタ−が形成されていないので、脱炭焼鈍における一次再結晶組織の調整が二次再結晶を制御するうえで重要となる。従来の高温スラブ加熱による方向性電磁鋼板の製造方法の研究においては、二次再結晶前の一次再結晶組織調整に関する知見はほとんどなく、本願発明者らは例えば特公平８−３２９２９号公報、特開平９−２５６０５１号公報等にその重要性を開示している。
【０００７】
特公平８−３２９２９号公報において、一次再結晶粒組織の粒径分布の変動係数が０．６より大きくなり粒組織が不均一になると二次再結晶が不安定になることを開示している。その後、さらに特開平９−２５６０５１号公報において、二次再結晶の制御因子である一次再結晶組織とインヒビターに関する研究を行なった結果、一次再結晶粒組織の粒組織として脱炭焼鈍後の集合組織においてゴス方位粒の成長を促進すると考えられる｛１１１｝方位および｛４１１｝方位の粒の比率；I｛１１１｝／I｛４１１｝を３以下に調整することにより製品の磁束密度が向上することを示した。ここで、I｛１１１｝及びI｛４１１｝はそれぞれ｛１１１｝及び｛４１１｝面が鋼板板面に平行である粒の割合であり、Ｘ線回折測定により板厚１/１０層において測定された回折強度値を表している。
【０００８】
この脱炭焼鈍後の一次再結晶組織に対しては、脱炭焼鈍工程の加熱速度、均熱温度、均熱時間等の脱炭焼鈍の焼鈍サイクルが影響するのはもちろんのこと、熱延板焼鈍の有無、冷間圧延の圧下率（冷延圧下率）等の脱炭焼鈍前の製造工程も影響を与える。これらの工程制御因子により制御した一次再結晶集合組織の影響を介して二次再結晶時に[110]<001>方位をもつ結晶粒の優先成長性が高まるが、この優先成長性にはインヒビターと呼ばれる析出物も影響を与える。
【０００９】
【発明が解決しようとする課題】
本発明は、インヒビター条件に応じて脱炭焼鈍条件を適切に制御することによって、工業的に安定して磁束密度の高い優れた磁気特性をもつ方向性電磁鋼板を製造する方法を開示するものである。
また、本発明は、薄手方向性電磁鋼板を低温スラブ加熱により製造する方法において、従来必須であった中間焼鈍を挟んだ二回以上の冷延工程を、酸可溶性Ａｌ量および脱炭焼鈍条件を適切に制御することにより一回のみの冷延によっても磁束密度の高い優れた磁気特性をもつ方向性電磁鋼板を製造する方法を提供するものである。
【００１０】
【課題を解決するための手段】
本発明の要旨とするところは以下の通りである。
（１）質量で、Ｓｉ：０．８〜４．８％、Ｃ：０．０８５％以下、酸可溶性Ａｌ：０．０１〜０．０６５％、Ｎ：０．０１２％以下を含み、あるいは更に必要に応じて、Ｓｎ：０．０２〜０．１５％、Ｃｒ：０．０３〜０．２％の１種または２種を含有し、残部Ｆｅ及び不可避的不純物からなる鋼を１２８０℃以下の温度で加熱した後に熱間圧延により熱延板となし、次いで一回もしくは中間焼鈍を挟む二回以上の、圧下率９０％超の冷間圧延により最終板厚とし、脱炭焼鈍後マグネシアを主成分とする焼鈍分離剤を塗布し、仕上げ焼鈍を施す方向性電磁鋼板の製造方法において、酸可溶性Alの量：[Al]％に対応して、脱炭焼鈍工程の昇温過程における、鋼板温度が６００℃以下の領域から７５０〜９００℃の範囲内の所定の温度までの加熱速度：HR℃／秒をHR≧−6250[Al]+200とすることにより、脱炭焼鈍後の集合組織におけるI[111]/I[411]の比率を１．７以上３以下に調整し、その後窒化処理を行なうことを特徴とする方向性電磁鋼板の製造方法。
【００１１】
（２）前記熱延板に９００〜１２００℃の温度域で３０秒〜３０分間の焼鈍を施すことを特徴とする（１）に記載の方向性電磁鋼板の製造方法。
（３）前記脱炭焼鈍工程において、７７０℃〜９００℃の温度域で雰囲気ガスの酸化度（ＰＨ_２Ｏ／ＰＨ_２）：０．１５超１．１以下の範囲内で鋼板の酸素量が２．３ｇ／ｍ² 以下となるような時間焼鈍することを特徴とする（１）又は（２）に記載の方向性電磁鋼板の製造方法。
【００１２】
（４）前記鋼板の酸可溶性Ａｌの量：［Ａｌ］に応じて窒素量：［Ｎ］が［Ｎ］/［Ａｌ］≧０．６７を満足する量となるように窒化処理を施すことを特徴とする（１）〜（３）のいずれかに記載の方向性電磁鋼板の製造方法。
【００１４】
【発明の実施の形態】
本発明者らは、一次再結晶組織のＩ｛１１１｝／Ｉ｛４１１｝を３以下となるように制御することにより、B8の値を1.88T以上にできることを特開平９−２５６０５１号公報にて明らかにしているが、製品の磁束密度に影響を及ぼす一次再結晶組織以外の主要因子であるインヒビターを制御することにより、一次再結晶集合組織制御の効果をより顕著に発揮することができるのではないかと考え、鋼板の磁束密度B8に対するインヒビターと一次再結晶集合組織制御因子との関係について調べた。ここでは特に、一次再結晶集合組織に影響を与える脱炭焼鈍時の加熱速度とインヒビター強度に関係する酸可溶性Alとの相関について詳細に調べた。その結果、酸可溶性Alの量に従って、高いB8を得るのに必要な加熱速度の領域が広がることが分かった。
【００１５】
以下、実験結果をもとに説明する。
図１はsol-Al量、脱炭焼鈍加熱速度に対する鋼板の磁束密度B8の分布を示した図である。ここで用いた試料は、質量％で、Ｓｉ：３．３％、Ｃ：０．０６％、酸可溶性Ａｌ：０．０２０−０．０３８％、Ｎ：０．００８％、Ｍｎ：０．１％、Ｓ：０．００７％を含有するスラブを１１５０℃の温度で加熱した後、２．０ｍｍ厚に熱間圧延し、その後、１１２０℃で焼鈍した後、０．２２ｍｍ厚まで冷間圧延後、加熱速度１５〜１００℃／秒で加熱し、７７０〜９５０℃の温度で脱炭焼鈍した後、一部はそのまま、一部はアンモニア含有雰囲気で焼鈍して鋼板中の窒素を０．０２〜０．０３％とし、次いで、ＭｇＯを主成分とする焼鈍分離剤を塗布した後、仕上げ焼鈍を行ったものである。これらの試料の脱炭焼鈍板の一次再結晶集合組織を解析した結果、全ての試料においてＩ｛１１１｝／Ｉ｛４１１｝の値が３以下となっていることを確認している。更に全く同様に０．１８ｍｍ厚まで冷延した実験でも図１と同様の結果が得られた。
【００１６】
図１から明らかなように、１．９２T以上の高磁束密度が得られる脱炭焼鈍加熱速度の閾値が酸可溶性Alの量：[Al]％が増加するに従って低下していくことがわかる。即ち、脱炭焼鈍時の加熱速度を同じとし、同じように一次再結晶集合組織を調整した場合であっても、インヒビターを強くするように[Al]を高くしさえすれば、一次再結晶集合組織制御による高磁束密度化の効果を得ることができるということである。
【００１７】
これまで方向性電磁鋼板の脱炭焼鈍を急速加熱で行うことは、例えば、特開平１−２９０７１６号公報、特開平６−２１２２６２号公報等に開示されている。しかしながら、これらの特許は高温スラブ加熱による方向性電磁鋼板の製造方法に適用したものであり、その効果も二次再結晶粒径が小さくなり鉄損特性が向上するというものである。
【００１８】
本発明の製品に及ぼす効果はこれらの結果と異なり磁束密度（Ｂ８）の向上に大きな影響を及ぼすものである。また、集合組織制御の効果を酸可溶性Al量や窒化量でインヒビターを制御することによって高磁束密度が得られるために必要な脱炭焼鈍時の加熱速度の下限値が下がるというものである。
上記の結果に対する理由について、本発明者らは次のように考えている。本発明における様な（Ａｌ，Ｓｉ）Ｎ等の窒化物のように熱的に安定な（強い）インヒビタ−を用いた場合には、粒界移動の粒界性格依存性が高くなるために、ゴス方位粒の数よりもゴス方位とΣ９対応方位関係にあるマトリックス粒（具体的には｛１１１｝＜１１２＞、｛４１１｝＜１４８＞）の数および結晶方位分散がより重要となるが、熱的に安定な（強い）インヒビタ−を増やすことによって、同様な結晶方位分散であっても高いB8が得られやすくなったということである。また、[Al]を増やすとインヒビターへの影響の他に、一次再結晶集合組織への効果もあり、このことも磁束密度を高くすることに対して相乗的に寄与したものと考えている。具体的には、実施例１に示してあるように[Al]を増やすとＩ｛１１１｝／Ｉ｛４１１｝の値が減少しており、このことは二次再結晶粒となる一次再結晶組織中の[１１０]＜００１＞方位粒の成長を促進する｛１１１｝方位粒と｛４１１｝方位粒のうち、結晶方位分散が小さい｛４１１｝方位粒の発達が促されたことを意味している。その結果として、２次再結晶粒（ゴス粒）の方位分散も小さくなり、高いＢ８が得られる。
【００１９】
本発明に用いる鋼の成分としては、Ｓｉ：０．８〜４．８％、Ｃ：０．０８５％以下、酸可溶性Ａｌ：０．０１〜０．０６５％、Ｎ：０．０１２％以下が必要である。
Ｓｉは添加量を多くすると電気抵抗が高くなり、鉄損特性が改善される。しかしながら、４．８％を超えると圧延時に割れやすくなってしまう。また、０．８％より少ないと仕上げ焼鈍時にγ変態が生じ結晶方位が損なわれてしまう。
【００２０】
Ｃは一次再結晶組織を制御するうえで有効な元素であるが、磁気特性に悪影響を及ぼすので仕上げ焼鈍前に脱炭する必要がある。Ｃが０．０８５％より多いと脱炭焼鈍時間が長くなり生産性が損なわれてしまう。
酸可溶性Ａｌは、本願発明においてＮと結合して（Ａｌ，Ｓｉ）Ｎとしてインヒビターとしての機能をはたすために必須の元素である。二次再結晶が安定する０．０１〜０．０６５％を限定範囲とする。
【００２１】
Ｎは０．０１２％をこえると冷延時にブリスターとよばれる鋼板中の空孔を生じる。
その他、Ｓは磁気特性に悪影響を及ぼすので０．０１５％以下とすることが望ましい。Ｓｎは脱炭焼鈍後の集合組織を改善し、二次再結晶を安定化するため０．０２〜０．１５％添加することが望ましい。Ｃｒは脱炭焼鈍の酸化層を改善し、グラス被膜形成に有効な元素であり、０．０３〜０．２％添加することが望ましい。その他、微量のＣｕ，Ｓｂ，Ｍｏ，Ｂｉ，Ｔｉ等を鋼中に含有することは、本発明の主旨を損なうものではない。
【００２２】
上記の組成を有する珪素鋼スラブは転炉、または電気炉等により鋼を溶製し、必要に応じて溶鋼を真空脱ガス処理し、ついで連続鋳造もしくは造塊後分塊圧延することによって得られる。その後、熱間圧延に先だってスラブ加熱が施される。本発明においては、スラブ加熱温度は１２８０℃以下として、先述の高温スラブ加熱の諸問題を回避する。
【００２３】
上記、熱間圧延板は、通常、磁気特性を高めるために９００〜１２００℃で３０秒〜３０分間の短時間焼鈍を施す。その後、一回もしくは焼鈍を挟んだ二回以上に冷間圧延により最終板厚とする。冷間圧延としては、特公昭４０ー１５６４４号公報に示されるように最終冷延圧下率を８０％以上とすることが、｛１１１｝、｛４１１｝等の一次再結晶方位を発達させるうえで必要である。特に、｛４１１｝の方位の発達が顕著になるように最終冷延圧下率を８５％以上とすることが望ましい。またさらに、冷延圧下率が９５％より大きくなってしまうと冷延工程での負荷が大きくなり、実操業の観点から９５％以下が現実的である。
また、本発明のポイントは高Ｂ８を得るために、インヒビターの強さに応じて脱炭焼鈍加熱速度を制御し、一次再結晶集合組織を制御する点にあるが、この制御技術によって、従来、冷延一回法においてはＢ８の劣化を招いていたような高冷延圧下率の条件においても極めて良好な二次再結晶を実現させることが可能となった。具体的には、例えば、中島らの論文（鉄と鋼７７（１９９１）ｐ．１７１０）などには、冷延圧下率の増加にともなってＢ８が向上し、圧下率が８８％で最高となり、９０％程度になると急激にＢ８の劣化が起こってしまうことが報告されているが、本発明では９０％超の圧下率においても高いＢ８が実現できる。このことは特に、従来二回冷延法でしか製造できなかった０．２０ｍｍ以下の薄手高Ｂ８材製造において、冷延一回法で製造することを可能とする。第４図にそれを導いた実験結果を示す。実験は［Ａｌ］が０．０３０％である板厚１．６〜２．８ｍｍの熱延板から冷延した板厚０．２０ｍｍの冷延板を６０℃／秒の加熱速度で室温から８００℃まで加熱した後、８００〜８５０℃の所定の温度において雰囲気ガスの酸化度０．５５で１２０秒焼鈍した。その後窒化処理により窒素量を０．０２０〜０．０３０％としたのちマグネシアを主成分とする焼鈍分離剤を塗布して仕上げ焼鈍を行った。図４から明らかなように９０％超の圧下率で特に高いＢ８を得ることができる。
【００２４】
冷間圧延後の鋼板は、鋼中に含まれるＣを除去するために湿潤雰囲気中で脱炭焼鈍を施す。その際、脱炭焼鈍加熱速度および脱炭焼鈍均熱温度等を制御し、脱炭焼鈍後の一次再結晶集合組織のI[111]／I[411]の値を３以下に調整することが磁気特性B8を１．８８T以上の製品を得るためにまず必要である。さらに、本発明のポイントである脱炭焼鈍工程の焼鈍サイクルにおける加熱速度：HR℃／秒を酸可溶性Alの量：[Al]％に対してHR≧−6250[Al]+200を満たすように調整することによってＢ８が１．９２T以上の製品を得ることができる（即ち、[Al]を多くしていった場合のHRの下限値は、HR≧−6250[Al]+200かつI[111]／I[411]の値が３以下となるために必要な加熱速度ということになる）。また、この加熱速度で加熱する必要がある温度域は少なくとも６００℃から７５０〜９００℃までの温度域である。
【００２５】
図２、図３に上記の結論を導いた実験結果を示す。[Al]が０．０２６％である冷延板を４０℃／秒の加熱速度で室温から６００℃〜１０００℃の温度域の所定の温度まで加熱した後、窒素ガスで室温まで冷却した。その後２０℃／秒の加熱速度で８５０℃まで加熱し、雰囲気ガスの酸化度０．３３で１２０秒焼鈍した。その後、窒化処理により窒素量を０．０２１％としたのちＭｇＯを主成分とする焼鈍分離剤を塗布して仕上げ焼鈍を行った。図２に示すように４０℃／秒の加熱速度での到達温度が７５０℃以上、９００℃以下の範囲で磁束密度が向上していることが分かる。７５０℃未満で効果が発揮されないのは、７５０℃未満では一次再結晶が十分に進行しておらず、一次再結晶集合組織を変えるためには再結晶を十分に進行させる必要があるためである。また、９００℃超の温度まで加熱すると、試料の一部に変態組織が生じ、その後の脱炭焼鈍完了時点での組織が混粒組織になるためであると考えられる。
【００２６】
次いで、上記冷延板を加熱速度２０℃／秒で３００℃から７５０℃の温度域の所定の温度まで加熱し、その温度から加熱速度４０℃／秒で８５０℃まで加熱した後、窒素ガスで室温まで冷却した。その後２０℃／秒の加熱速度で８５０℃まで加熱し、雰囲気ガスの酸化度０．３３で１２０秒焼鈍した。その後窒化処理により窒素量を０．０２１％としたのちＭｇＯを主成分とする焼鈍分離剤を塗布して仕上げ焼鈍を行った。図３に示すように加熱速度４０℃／秒の加熱開始温度が６００℃超では磁束密度向上効果が無いことが分かる。
【００２７】
これらの結果から、加熱速度４０℃／秒以上で加熱する必要がある温度域は少なくとも６００℃から７５０〜９００℃までの温度域であることが分かる。従って、脱炭焼鈍工程の昇温過程において鋼板温度が６００℃以下の温度域から４０℃／秒以上で加熱することが必要となる。また、上記のような脱炭焼鈍工程の昇温過程での加熱は冷延工程から脱炭焼鈍工程の間に加熱焼鈍を行ったとしても本発明の趣旨を損なうものではない。
【００２８】
また、上記の加熱速度の調整の効果を安定して発揮させるためには後述の実施例４に示しているように、加熱した後に７７０〜９００℃の温度域で雰囲気ガスの酸化度（ＰH₂O／ＰH₂）を０．１５超１．１以下として鋼板の酸素量を２．３ｇ/ｍ²以下とすることが有効である。雰囲気ガスの酸化度が０．１５未満では鋼板表面に形成されるグラス被膜の密着性が劣化し、１．１を越えるとグラス被膜に欠陥が生じる。特に、昇温段階での加熱速度を40℃/s以上に高めた場合には均熱時の酸化が促進されるので、酸素量を一定の範囲内に管理するためには雰囲気酸化度を低めにする、または均熱時間を短くする必要がある。
【００２９】
加熱の方法は特に限定するものではなく、４０〜１００℃／秒程度の加熱速度に対しては、従来の通常輻射熱を利用したラジアントチューブや発熱体による脱炭焼鈍設備を改造した設備、また１００℃／秒以上の加熱速度に対しては、新たなレーザー、プラズマ等の高エネルギー熱源を利用する方法、誘導加熱、通電加熱装置等を適用することができる。また、従来の通常輻射熱を利用したラジアントチューブや発熱体による脱炭焼鈍設備に新たなレーザー、プラズマ等の高エネルギー熱源を利用する方法、誘導加熱、通電加熱装置等を適用する方法等を組み合わせることも有効である。
【００３０】
均熱温度に関しては、例えば特開平２−１８２８６６号公報に示されるような一次再結晶粒組織の調整を勘案して設定する。通常は７７０〜９００℃の範囲で行う。また、均熱の前段で脱炭した後に、粒調整のために均熱の後段の温度を高めることや後段の雰囲気ガスの酸化度を下げて均熱時間をのばすことも有効である。
【００３１】
窒化処理としては、アンモニア等の窒化能のあるガスを含有する雰囲気中で焼鈍する方法、ＭｎＮ等の窒化能のある粉末を焼鈍分離剤中に添加して仕上げ焼鈍中に行う方法等がある。脱炭焼鈍の加熱速度を高めた場合に二次再結晶を安定的に行わせるためは、（Ａｌ，Ｓｉ）Ｎの組成比率を調整する必要があり、窒化処理後の窒素量としては鋼中のＡｌ量に対してＮ／Ａｌを質量比として０．６７以上とする必要がある。
【００３２】
その後、マグネシアを主成分とする焼鈍分離剤を塗布した後に、仕上げ焼鈍を行い｛１１０｝＜００１＞方位粒を二次再結晶により優先成長させる。
【００３３】
【実施例】
＜実施例１＞
重量％で、Ｓｉ：３．３％、Ｃ：０．０６％、酸可溶性Ａｌ：０．０２０、０．０２６、０．０３１％、Ｎ：０．００８％、Ｍｎ：０．１％、Ｓ：０．００７％含有するスラブを１１５０℃の温度で加熱した後、２．０ｍｍ厚に熱間圧延した。その後、１１２０℃で焼鈍した後、０．２２ｍｍ厚まで冷間圧延後、脱炭焼鈍の加熱速度を１５〜１００℃／秒とし、８３０〜８６０℃の温度で脱炭焼鈍した後、アンモニア含有雰囲気で焼鈍して鋼板中の窒素を０．０２〜０．０３％とした。ついでＭｇＯを主成分とする焼鈍分離剤を塗布した後、仕上げ焼鈍を行った。製品の特性値を表１に示す。一次再結晶集合組織に関してI[111]/I[411]の値が３以下であり、脱炭焼鈍工程の加熱速度：HRが酸可溶性Alの量：[Al]％に対してHR≧−6250[Al]+200を満足する場合、Ｂ８が１．９２Ｔ以上の高い磁束密度を得られていることが分かる。換言すれば、[Al]を増加させた場合、同じ脱炭焼鈍速度に対するB8が向上し、高いB8を得られる脱炭焼鈍加熱速度の領域が小さな加熱速度の領域まで広がっていることがわかる。
【００３４】
【表１】

【００３５】
＜実施例２＞
質量％で、Ｓｉ：３．３％、Ｃ：０．０５％、酸可溶性Ａｌ：０．０２７、０．０３１％、Ｎ：０．００７％、Ｃｒ：０．１％、Ｓｎ：０．０５％、Ｍｎ：０．１％、Ｓ：０．００８％含有するスラブを１１５０℃の温度で加熱した後、熱間圧延によって、２．０mm厚にし、この熱間圧延板を１１２０℃で焼鈍し、その後、０．２２ｍｍ厚に冷間圧延した。この冷延板を１０〜６００℃／秒の加熱速度で８００℃に加熱した後、８００〜８９０℃で１２０秒間、雰囲気酸化度０．４４で脱炭焼鈍した。この時の鋼板の酸素量は１．９〜２．１ｇ／ｍ²であった。
【００３６】
その後、７５０℃で３０秒間アンモニア含有雰囲気中で焼鈍し、アンモニア含有量を変えることにより鋼板中の窒素量を０．０２３〜０．０２９％とした。その後、マグネシアを主成分とする焼鈍分離剤を塗布した後、１２００℃で２０時間仕上げ焼鈍を施した。
これらの試料に張力コーテイング処理を施した。得られた製品の特性を表２に示す。表２より、一次再結晶集合組織に関してI[111]/I[411]の値が３以下であり、脱炭焼鈍工程の加熱速度：HRが酸可溶性Alの量：[Al]％に対してHR≧−6250[Al]+200を満足する場合、Ｂ８が１．９２Ｔ以上の高い磁束密度を得られていることが分かる。また特に、HRが７５℃／秒〜１４０℃／秒で特にB8が高く、その領域が[Al]が増えると下限側に広がることがわかる。
【００３７】
【表２】

【００３８】
＜実施例３＞
質量％で、Ｓｉ：３．２％、Ｍｎ：０．１％、Ｃ：０．０５％、Ｓ：０．００８％、酸可溶性Ａｌ：０．０２４％、Ｎ：０．００８％、Ｓｎ：０．０５％を含む板厚２．０ｍｍ珪素鋼熱延板を最終板厚０．２２ｍｍに冷延した。この冷延板を酸化度０．３３の窒素と水素の混合ガス中において、加熱速度（１）２０℃／秒（２）１００℃／秒で８４０℃まで加熱し８４０℃で１５０秒焼鈍し一次再結晶させた。その後、７５０℃で３０秒間アンモニア含有雰囲気中で焼鈍し、アンモニア含有量を変えることにより鋼板中の窒素量を０．０２２〜０．０２６％とした。
【００３９】
これらの鋼板にマグネシアを主成分とする焼鈍分離剤を塗布した後、仕上げ焼鈍を施した。仕上げ焼鈍は１２００℃まではＮ₂：２５％+Ｈ₂：７５％の雰囲気ガス中で１５℃／ｈｒの加熱速度で行い、１２００℃でＨ2：１００％に切りかえ２０時間焼鈍を行った。
これらの試料を張力コーテイング処理を施した。得られた製品の磁気特性を表３に示す。実施例１、２と比較すると、冷延前の焼鈍を行っていないので全体の磁束密度は低いが、本発明の磁束密度向上効果が確認できる。
【００４０】
【表３】

【００４１】
＜実施例４＞
質量％で、Ｓｉ：３．２％、Ｃ：０．０５％、酸可溶性Ａｌ：０．０２９％、Ｎ：０．００８％、Ｍｎ：０．１％、Ｓ：０．００７％、含有する珪素鋼スラブを１１００℃に加熱し、２．０ｍｍ厚とした。この熱間圧延板を１１００℃で焼鈍し、冷間圧延し最終板厚０．２ｍｍとした。その後、加熱速度１００℃／秒で８５０℃まで加熱した後に室温まで冷却した。その後加熱速度３０℃／秒で加熱し、８３０℃で、酸化度０．１２〜０．７２の雰囲気ガスで９０秒間焼鈍した後、アンモニア含有雰囲気中で７５０℃で３０秒焼鈍し、鋼板中の窒素量を０．０２〜０．０３％とした。次いで、ＭｇＯを主成分とする焼鈍分離剤を塗布した後、１２００℃で２０時間仕上げ焼鈍を施した。
【００４２】
製品の特性を表４に示す。表４より、本発明で規定した雰囲気の酸化度０．１５超１．１以下の範囲および、脱炭焼鈍後の酸素量２．３ｇ／ｍ²以下の範囲を外れた場合には製品のグラス被膜特性が劣化していることがわかる。
【００４３】
【表４】

【００４４】
＜実施例５＞
質量％で、Ｓｉ：３．２％、Ｃ：０．０５％、酸可溶性Ａｌ：０．０２４％、Ｎ：０．００７％、Ｃｒ：０．１％、Ｓｎ：０．０５％、Ｍｎ：０．１％、Ｓ：０．００８％を含有する珪素鋼スラブを１１５０℃加熱し、板厚２．３ｍｍに熱間圧延した。この熱間圧延板を１１２０℃で焼鈍し、その後、０．２２ｍｍ厚に冷間圧延した。この冷延板を１００℃／秒で８００℃に加熱した後、８２０℃で９０〜６００秒間、雰囲気酸化度０．５２で脱炭焼鈍し、Ｉ｛１１１｝／Ｉ｛４１１｝の値を２．７以下にし、一次再結晶集合組織を請求項1の不等式が成り立つよう調整した。その後、７５０℃で３０秒間アンモニア含有雰囲気中で焼鈍し、鋼板中の窒素量を０．０２３〜０．０２９％とした。ＭｇＯを主成分とする焼鈍分離剤を塗布した後、１２００℃で２０時間仕上げ焼鈍を施した。
【００４５】
製品の特性値を表５に示す。鋼板の酸素量が２．４１ｇ／ｍ²と多くなった場合には、磁気特性が劣化していることが分かる。
【００４６】
【表５】

【００４７】
＜実施例６＞
質量％で、Ｓｉ：３．２％、Ｃ：０．０５％、酸可溶性Ａｌ：０．０２４％、Ｎ：０．００７％、Ｃｒ：０．１％、Ｓｎ：０．０５％、Ｍｎ：０．１％、Ｓ：０．００８％含有する珪素鋼スラブを１１５０℃加熱し、板厚２．３ｍｍに熱間圧延した。この熱間圧延板を１１２０℃で焼鈍し、その後、０．２２ｍｍ厚に冷間圧延した。この冷延板を１００℃／秒で８００℃に加熱した後、８２０℃で１１０秒間、雰囲気酸化度０．４４で脱炭焼鈍した。集合組織：Ｉ｛１１１｝／Ｉ｛４１１｝の値は１．７、鋼板酸素量は１．９ｇ／ｍ²であった。その後、７５０℃で３０秒間アンモニア含有雰囲気中で焼鈍し、アンモニア含有量を変えることにより鋼板中の窒素量を０．０１２〜０．０２６％とした。その後、マグネシアを主成分とする焼鈍分離剤を塗布した後、１２００℃で２０時間仕上げ焼鈍を施した。
【００４８】
製品の特性値を表６に示す。窒化処理後の窒素量が０．０１７％以上（［Ｎ］／［Ａｌ］≧０．６７）で磁束密度が高くなることが分かる。
【００４９】
【表６】

【００５０】
＜実施例７＞
質量％で、Ｓｉ：３．３％、Ｃ：０．０６％、酸可溶性Ａｌ：０．０２０，０．０２６，０．０３１％、Ｎ：０．００８％、Ｍｎ：０．１％、Ｓ：０．００７％含有するスラブを１１５０℃の温度で加熱した後、２．０ｍｍ厚に熱間圧延した。その熱延板を、前段１１２０℃、後段９００℃で焼鈍した後、０．１５ｍｍ厚まで冷間圧延後、脱炭焼鈍の加熱速度を１５〜１００℃／秒とし、８１０〜８６０℃の温度で脱炭焼鈍した後、アンモニア含有雰囲気で焼鈍して鋼板中の窒素を０．０２〜０．０３％とした。ついでマグネシアを主成分とする焼鈍分離剤を塗布した後、仕上げ焼鈍を行った。
製品の特性値を表７に示す。脱炭焼鈍工程の加熱速度：ＨＲが酸可溶性Ａｌの量：［Ａｌ］％に対してＨＲ≧−６２５０［Ａｌ］＋２００となっている場合、Ｂ８が１．９２Ｔ以上の高い磁束密度を得られていることが分かる。
【００５１】
【表７】

【００５２】
＜実施例８＞
質量％で、Ｓｉ：３．３％、Ｃ：０．０５％、酸可溶性Ａｌ：０．０２５％，０．０３５％、Ｎ：０．００７％、Ｃｒ：０．１％、Ｓｎ：０．０５％、Ｍｎ：０．１％、Ｓ：０．００８％含有するスラブを１１５０℃の温度で加熱した後、熱間圧延によって、２．３ｍｍ厚にし、この熱間圧延板を１１２０℃で焼鈍し、その後、０．１８ｍｍ厚に冷間圧延した。この冷延板を５〜６００℃／秒の加熱速度で８００℃に加熱した後、８００〜８９０℃で１２０秒間、雰囲気酸化度０．５２で脱炭焼鈍し、一次再結晶集合組織を図１で示した高Ｂ８が得られる領域に調整した。その後、７５０℃で３０秒間アンモニア含有雰囲気中で焼鈍し、アンモニア含有量を変えることにより鋼板中の窒素量を０．０２５〜０．０３５％とした。その後、マグネシアを主成分とする焼鈍分離剤を塗布した後、１２００℃で２０時間仕上げ焼鈍を施した。
得られた製品の特性を表８に示す。表８より、脱炭焼鈍工程の加熱速度：ＨＲが酸可溶性Ａｌの量：［Ａｌ］％に対してＨＲ≧−６２５０［Ａｌ］＋２００となっている場合、Ｂ８が１．９２Ｔ以上の高い磁束密度を得られていることが分かる。特に、［Ａｌ］を増加された場合、冷延一回法による高Ｂ８効果がより顕著に見られ、脱炭焼鈍加熱速度が小さくても高Ｂ８効果が得られると共に、より高いＢ８をえることができる。
【００５３】
【表８】

【００５４】
【発明の効果】
本発明により、従来の高温スラブ加熱に起因する諸問題の無い低温スラブ加熱による方向性電磁鋼板の製造方法を基に、一次再結晶組織、酸可溶性Alに対する脱炭焼鈍条件、表面酸化層及び窒化量を規定することにより、磁束密度の高い優れた磁気特性をもつ方向性電磁鋼板を工業的に安定して製造することができる。特に、一回冷延法を前提とした製造方法において、酸可溶性Ａｌに対する脱炭焼鈍条件及び窒化量を規定することにより、磁束密度が高い優れた磁気特性をもつ薄手方向性電磁鋼板を工業的に安定して製造することができる。このことにより、熱延に負荷が少なく、中間焼鈍を省略し、従来よりも安価かつ鉄損に優れた方向性電磁鋼板を得ることができる。
【図面の簡単な説明】
【図１】製品の磁束密度（Ｂ８）に及ぼす酸可溶性Alと脱炭焼鈍加熱速度の影響を示した図である。
【図２】磁束密度に及ぼす脱炭焼鈍の急速加熱完了温度の影響を示した図である。
【図３】磁束密度に及ぼす脱炭焼鈍の急速加熱開始温度の影響を示した図である。
【図４】磁束密度に及ぼす冷延圧下率の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 so-called grain-oriented electrical steel sheet in which crystal grains are accumulated in a {110} <001> orientation with a Miller index. This steel plate is used as an iron core of electrical equipment such as a transformer as a soft magnetic material.
[0002]
[Prior art]
The grain-oriented electrical steel sheet is a steel sheet containing 4.8% or less of Si composed of crystal grains accumulated in {110} <001> orientation (so-called Goth orientation). This steel plate is required to have excitation characteristics and iron loss as magnetic characteristics. As an index representing the excitation characteristics, a magnetic flux density B8 at a magnetic field strength of 800 A / m is usually used. Further, as an index representing the iron loss characteristic, iron loss per kg of steel sheet: W17 / 50 when magnetized to 1.7 T at a frequency of 50 Hz is used. Magnetic flux density: B8 is the largest governing factor of the iron loss characteristic, and the higher the magnetic flux density: B8 value, the better the iron loss characteristic. In order to increase the magnetic flux density B8, it is important to align the crystal orientation at a high level. This control of crystal orientation is achieved by utilizing a catastrophic grain growth phenomenon called secondary recrystallization.
[0003]
In order to control this secondary recrystallization, it is necessary to adjust the primary recrystallization structure before the secondary recrystallization and to adjust fine precipitates called inhibitors. This inhibitor has a function of suppressing the growth of general grains in the primary recrystallization structure and preferentially growing only specific {110} <001> oriented grains.
Typical examples of precipitates include M.P. F. Littmann (Japanese Patent Publication No. 30-3651) and J.A. E. May & D. Turnbull (Trans.Met.Soc.AIME212 (1958) p769) and others are MnS, Taguchi et al. (Japanese Patent Publication No. 40-15644) are AlN, Imanaka et al. Presenting.
[0004]
These precipitates are completely dissolved during slab heating before hot rolling, and then finely precipitated by hot rolling and subsequent annealing. In order to completely dissolve these precipitates, it is necessary to heat at a high temperature of 1350 ° C. to 1400 ° C. or more, which is about 200 ° C. higher than the slab heating temperature of ordinary steel and has the following problems. (1) A dedicated heating furnace is required. (2) The energy intensity of the heating furnace is high. (3) The amount of melt scale is large and operation management such as so-called no-roll out is necessary.
[0005]
Therefore, research and development by low-temperature slab heating has been advanced, and as a manufacturing method by low-temperature slab heating, Komatsu et al. (Japanese Patent Publication No. 62-45285) discloses a method of using (Al, Si) N formed by nitriding as an inhibitor. Yes. As a method of nitriding treatment, Kobayashi et al. Disclosed a method of nitriding in strip form after decarburization annealing (JP-A-2-77525), and Ushigami et al. Reported the behavior of the nitride (Materials Science). Forum, 204-206 (1996), pp593-598).
[0006]
In the method for producing grain-oriented electrical steel sheets by low-temperature slab heating, since the inhibitor is not formed during decarburization annealing, adjustment of the primary recrystallization structure in decarburization annealing is important in controlling secondary recrystallization. . In the study of the conventional method for producing grain-oriented electrical steel sheets by high-temperature slab heating, there is almost no knowledge about primary recrystallization structure adjustment before secondary recrystallization, and the inventors of the present application have disclosed, for example, Japanese Patent Publication No. 8-32929. The importance is disclosed in Japanese Laid-Open Patent Publication No. 9-256051.
[0007]
Japanese Patent Publication No. 8-32929 discloses that the secondary recrystallization becomes unstable when the variation coefficient of the particle size distribution of the primary recrystallized grain structure is larger than 0.6 and the grain structure becomes non-uniform. . Thereafter, in JP-A-9-256051, as a result of research on the primary recrystallized structure and inhibitor which are the control factors of secondary recrystallization, the texture after decarburization annealing as the grain structure of the primary recrystallized grain structure The ratio of grains with {111} and {411} orientation, which is considered to promote the growth of goth-oriented grains in the above; the magnetic flux density of the product is improved by adjusting I {111} / I {411} to 3 or less showed that. Here, I {111} and I {411} are the proportions of grains whose {111} and {411} planes are parallel to the steel plate surface, respectively, and are measured at a plate thickness of 1/10 by X-ray diffraction measurement. Represents the diffraction intensity value.
[0008]
The primary recrystallized structure after this decarburization annealing is of course affected by the annealing cycle of decarburization annealing such as heating rate, soaking temperature, soaking time, etc. in the decarburizing annealing process. Production processes before decarburization annealing such as presence / absence of annealing and cold rolling reduction ratio (cold rolling reduction ratio) are also affected. Through the influence of primary recrystallization texture controlled by these process control factors, the preferential growth of grains with [110] <001> orientation is enhanced during secondary recrystallization. Called deposits also have an effect.
[0009]
[Problems to be solved by the invention]
The present invention discloses a method for producing a grain-oriented electrical steel sheet having excellent magnetic properties that are industrially stable and have high magnetic flux density by appropriately controlling decarburization annealing conditions according to inhibitor conditions. is there.
Further, in the method of manufacturing a thin grain-oriented electrical steel sheet by low-temperature slab heating, the present invention performs two or more cold rolling steps sandwiching intermediate annealing, which has been essential in the past, with acid-soluble Al content and decarburization annealing conditions. The present invention provides a method for producing a grain-oriented electrical steel sheet having excellent magnetic properties with a high magnetic flux density even by cold rolling only once by appropriate control.
[0010]
[Means for Solving the Problems]
The gist of the present invention is as follows.
(1) By mass, Si: 0.8 to 4.8%, C: 0.085% or less, acid-soluble Al: 0.01 to 0.065%, N: 0.012% or less, or further If necessary, steel containing Sn or 0.02 to 0.15%, Cr or 0.03 to 0.2%, or the balance Fe and unavoidable impurities is 1280 ° C or less. After heating at a temperature, a hot-rolled sheet is formed by hot rolling, and then the final sheet thickness is obtained by cold rolling with a rolling reduction of over 90% once or two or more times with intermediate annealing, and magnesia is mainly used after decarburization annealing. In the method for producing grain-oriented electrical steel sheets, in which an annealing separator as a component is applied and finish annealing is performed, the steel sheet temperature in the temperature rising process of the decarburization annealing process corresponding to the amount of acid-soluble Al: [Al]% Heating rate from a region of 600 ° C. or lower to a predetermined temperature in the range of 750 to 900 ° C. : The ratio of I [111] / I [411] in the texture after decarburization annealing is adjusted to 1.7 or more and 3 or less by setting HR ° C./second to HR ≧ −6250 [Al] +200. A method for producing a grain-oriented electrical steel sheet, wherein nitriding is performed thereafter.
[0011]
( 2 ) The method for producing a grain-oriented electrical steel sheet according to (1 ), wherein the hot-rolled sheet is annealed in a temperature range of 900 to 1200 ° C. for 30 seconds to 30 minutes.
( 3 ) In the decarburization annealing step, the oxygen content of the steel sheet is within the range of oxidization degree (PH ₂ O / PH ₂ ): 0.15 to 1.1 in the temperature range of 770 ° C. to 900 ° C. The method for producing a grain-oriented electrical steel sheet according to (1) or (2) , characterized in that annealing is performed for a time such that 2.3 g / m ² or less.
[0012]
( 4 ) The nitriding treatment is performed so that the amount of nitrogen: [N] satisfies [N] / [Al] ≧ 0.67 in accordance with the amount of acid-soluble Al in the steel sheet: [Al]. The manufacturing method of the grain-oriented electrical steel sheet according to any one of (1) to ( 3 ), which is characterized.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Japanese Patent Laid-Open No. 9-256051 discloses that the value of B8 can be made 1.88 T or more by controlling I {111} / I {411} of the primary recrystallization structure to be 3 or less. However, by controlling the inhibitor, which is a major factor other than the primary recrystallization structure that affects the magnetic flux density of the product, the effect of controlling the primary recrystallization texture can be exhibited more significantly. The relationship between the inhibitor for the magnetic flux density B8 of the steel sheet and the primary recrystallization texture control factor was investigated. Here, in particular, the correlation between the heating rate during decarburization annealing affecting the primary recrystallization texture and the acid-soluble Al related to the inhibitor strength was investigated in detail. As a result, it was found that the region of the heating rate necessary to obtain high B8 was expanded according to the amount of acid-soluble Al.
[0015]
Hereinafter, description will be given based on the experimental results.
FIG. 1 is a view showing the distribution of the magnetic flux density B8 of the steel sheet with respect to the sol-Al amount and the decarburization annealing heating rate. The sample used here is mass%, Si: 3.3%, C: 0.06%, acid-soluble Al: 0.020-0.038%, N: 0.008%, Mn: 0.1 %, S: A slab containing 0.007% is heated at a temperature of 1150 ° C., hot-rolled to a thickness of 2.0 mm, annealed at 1120 ° C., and then cold-rolled to a thickness of 0.22 mm. Then, after heating at a heating rate of 15 to 100 ° C./second and decarburizing annealing at a temperature of 770 to 950 ° C., a part is left as it is, a part is annealed in an ammonia-containing atmosphere, and nitrogen in the steel sheet is changed to 0.02 to Next, after applying an annealing separator mainly composed of MgO to 0.03%, finish annealing is performed. As a result of analyzing the primary recrystallization texture of the decarburized and annealed plates of these samples, it was confirmed that the value of I {111} / I {411} was 3 or less in all samples. Furthermore, the same result as in FIG. 1 was obtained in the experiment in which the film was cold-rolled to a thickness of 0.18 mm.
[0016]
As is apparent from FIG. 1, it can be seen that the decarburization annealing heating rate threshold at which a high magnetic flux density of 1.92 T or more is obtained decreases as the amount of acid-soluble Al: [Al]% increases. That is, even when the heating rate during decarburization annealing is the same and the primary recrystallization texture is adjusted in the same way, as long as [Al] is increased to strengthen the inhibitor, the primary recrystallization assembly This means that the effect of increasing the magnetic flux density by controlling the structure can be obtained.
[0017]
Performing decarburization annealing of grain-oriented electrical steel sheets by rapid heating is disclosed in, for example, Japanese Patent Application Laid-Open Nos. 1-290716 and 6-212262. However, these patents are applied to a method for producing grain-oriented electrical steel sheets by high-temperature slab heating, and the effect is that the secondary recrystallization grain size is reduced and the iron loss characteristics are improved.
[0018]
Unlike these results, the effect on the product of the present invention greatly affects the improvement of the magnetic flux density (B8). Further, the lower limit value of the heating rate at the time of decarburization annealing required for obtaining a high magnetic flux density by controlling the inhibitor by the amount of acid-soluble Al or the amount of nitriding as an effect of texture control is lowered.
The present inventors consider the reason for the above results as follows. When a thermally stable (strong) inhibitor such as a nitride such as (Al, Si) N in the present invention is used, the grain boundary character dependence of grain boundary movement is increased. Although the number of matrix grains (specifically, {111} <112>, {411} <148>) and the crystal orientation dispersion are more important than the number of Goth orientation grains, By increasing the number of thermally stable (strong) inhibitors, high B8 can be easily obtained even with similar crystal orientation dispersion. Moreover, increasing [Al] has an effect on the primary recrystallization texture in addition to the influence on the inhibitor, which is considered to have contributed synergistically to increasing the magnetic flux density. Specifically, as shown in Example 1, when [Al] is increased, the value of I {111} / I {411} decreases, which is the primary recrystallization that becomes the secondary recrystallized grains. This means that among the {111} and {411} oriented grains that promote the growth of [110] <001> oriented grains in the structure, the development of {411} oriented grains with a small crystal orientation dispersion was promoted. ing. As a result, the orientational dispersion of secondary recrystallized grains (goth grains) is also reduced, and high B8 is obtained.
[0019]
As steel components used in the present invention, Si: 0.8 to 4.8%, C: 0.085% or less, acid-soluble Al: 0.01 to 0.065%, N: 0.012% or less. is necessary.
When Si is added in an increased amount, the electrical resistance increases and the iron loss characteristics are improved. However, if it exceeds 4.8%, it tends to break during rolling. On the other hand, if it is less than 0.8%, the γ transformation occurs during finish annealing and the crystal orientation is impaired.
[0020]
C is an effective element for controlling the primary recrystallization structure, but it has an adverse effect on the magnetic properties, so it needs to be decarburized before finish annealing. When C is more than 0.085%, the decarburization annealing time becomes long and the productivity is impaired.
Acid-soluble Al is an essential element for binding to N and acting as an inhibitor as (Al, Si) N in the present invention. The limiting range is 0.01 to 0.065% at which secondary recrystallization is stabilized.
[0021]
When N exceeds 0.012%, voids in the steel sheet called blisters are produced during cold rolling.
In addition, since S adversely affects the magnetic characteristics, it is desirable to make it 0.015% or less. Sn is preferably added in an amount of 0.02 to 0.15% in order to improve the texture after decarburization annealing and stabilize secondary recrystallization. Cr improves the oxide layer of decarburization annealing and is an effective element for glass coating formation, and it is desirable to add 0.03 to 0.2%. In addition, containing a trace amount of Cu, Sb, Mo, Bi, Ti or the like in the steel does not impair the gist of the present invention.
[0022]
A silicon steel slab having the above composition is obtained by melting steel in a converter, electric furnace, or the like, subjecting the molten steel to vacuum degassing as necessary, and then performing continuous casting or block rolling after ingot forming. . Thereafter, slab heating is performed prior to hot rolling. In the present invention, the slab heating temperature is set to 1280 ° C. or less to avoid the above-described problems of high-temperature slab heating.
[0023]
The above hot-rolled sheet is usually annealed at 900 to 1200 ° C. for 30 seconds to 30 minutes in order to enhance magnetic properties. Thereafter, the final thickness is obtained by cold rolling at least once or two or more times with annealing. As for cold rolling, as shown in Japanese Patent Publication No. 40-15644, the final cold rolling reduction is 80% or more in order to develop the primary recrystallization orientation of {111}, {411}, etc. is necessary. In particular, it is desirable that the final cold rolling reduction is 85% or more so that the development of the {411} orientation becomes remarkable. Furthermore, if the cold rolling reduction ratio is greater than 95%, the load in the cold rolling process increases, and it is realistic that it is 95% or less from the viewpoint of actual operation.
In addition, the point of the present invention is to control the decarburization annealing heating rate according to the strength of the inhibitor and to control the primary recrystallization texture in order to obtain high B8. In the single cold rolling method, it was possible to realize a very good secondary recrystallization even under conditions of a high cold rolling reduction ratio that caused the deterioration of B8. Specifically, for example, in Nakashima et al.'S paper (Iron and Steel 77 (1991) p. 1710) and the like, B8 improves as the cold rolling reduction increases, and the reduction is the highest at 88%. Although it has been reported that B8 is rapidly deteriorated at about 90%, in the present invention, high B8 can be realized even at a rolling reduction of over 90%. In particular, this makes it possible to manufacture by a single cold rolling method in manufacturing a thin high B8 material having a thickness of 0.20 mm or less, which could be manufactured only by the conventional cold rolling method. Fig. 4 shows the experimental results that led to this. In the experiment, a cold-rolled sheet having a thickness of 0.20 mm that was cold-rolled from a hot-rolled sheet having a thickness of 1.6 to 2.8 mm with [Al] of 0.030% was heated from room temperature to 800 ° C. at a heating rate of 60 ° C./second. After heating to ° C., annealing was performed at a predetermined temperature of 800 to 850 ° C. for 120 seconds with an atmospheric gas oxidation degree of 0.55. Thereafter, the amount of nitrogen was set to 0.020 to 0.030% by nitriding treatment, and then an annealing separator containing magnesia as a main component was applied and finish annealing was performed. As is apparent from FIG. 4, a particularly high B8 can be obtained at a rolling reduction of more than 90%.
[0024]
The steel sheet after cold rolling is subjected to decarburization annealing in a humid atmosphere in order to remove C contained in the steel. In that case, the decarburization annealing heating rate, the decarburization annealing soaking temperature, etc. are controlled, and the value of I [111] / I [411] of the primary recrystallization texture after decarburization annealing can be adjusted to 3 or less. First, it is necessary to obtain a product having a magnetic property B8 of 1.88 T or more. Furthermore, the heating rate in the annealing cycle of the decarburization annealing process, which is the point of the present invention: HR ° C./second is set so as to satisfy HR ≧ −6250 [Al] +200 with respect to the amount of acid-soluble Al: [Al]%. By adjusting, a product having B8 of 1.92 T or more can be obtained (that is, when [Al] is increased, the lower limit value of HR is HR ≧ −6250 [Al] +200 and I [111] ] / I [411] is a heating rate necessary for the value to be 3 or less). Moreover, the temperature range which needs to be heated at this heating rate is a temperature range from at least 600 ° C. to 750 to 900 ° C.
[0025]
2 and 3 show the experimental results that led to the above conclusion. A cold-rolled sheet having [Al] of 0.026% was heated from room temperature to a predetermined temperature in the temperature range of 600 ° C. to 1000 ° C. at a heating rate of 40 ° C./second, and then cooled to room temperature with nitrogen gas. Thereafter, the sample was heated to 850 ° C. at a heating rate of 20 ° C./second, and annealed for 120 seconds at an oxidation degree of atmospheric gas of 0.33. Thereafter, the amount of nitrogen was set to 0.021% by nitriding treatment, and then an annealing separator containing MgO as a main component was applied and finish annealing was performed. As shown in FIG. 2, it can be seen that the magnetic flux density is improved when the temperature reached at a heating rate of 40 ° C./second is in the range of 750 ° C. to 900 ° C. The effect is not exhibited below 750 ° C. because primary recrystallization does not proceed sufficiently below 750 ° C., and recrystallization needs to proceed sufficiently to change the primary recrystallization texture. . Further, when heated to a temperature exceeding 900 ° C., it is considered that a transformation structure is generated in a part of the sample, and the structure at the time when the subsequent decarburization annealing is completed becomes a mixed grain structure.
[0026]
Next, the cold-rolled sheet is heated at a heating rate of 20 ° C./second to a predetermined temperature in the temperature range of 300 ° C. to 750 ° C., and heated from that temperature to 850 ° C. at a heating rate of 40 ° C./second, and then with nitrogen gas. Cooled to room temperature. Thereafter, the sample was heated to 850 ° C. at a heating rate of 20 ° C./second, and annealed for 120 seconds at an oxidation degree of atmospheric gas of 0.33. Thereafter, the amount of nitrogen was adjusted to 0.021% by nitriding treatment, and then an annealing separator containing MgO as a main component was applied and finish annealing was performed. As shown in FIG. 3, it can be seen that when the heating start temperature at a heating rate of 40 ° C./sec exceeds 600 ° C., there is no effect of improving the magnetic flux density.
[0027]
From these results, it is understood that the temperature range that needs to be heated at a heating rate of 40 ° C./second or more is a temperature range of at least 600 ° C. to 750 to 900 ° C. Accordingly, it is necessary to heat the steel sheet at a temperature of 40 ° C./second or more from a temperature range of 600 ° C. or less in the temperature raising process of the decarburization annealing process. Further, the heating in the temperature raising process of the decarburization annealing process as described above does not impair the gist of the present invention even if the heat annealing is performed between the cold rolling process and the decarburization annealing process.
[0028]
In order to stably exhibit the effect of adjusting the heating rate, as shown in Example 4 described later, the degree of oxidation of the atmospheric gas (PH _{2) in} the temperature range of 770 to 900 ° C. after heating is performed. It is effective that O / PH ₂ ) is more than 0.15 and 1.1 or less, and the oxygen content of the steel sheet is 2.3 g / m ² or less. If the degree of oxidation of the atmospheric gas is less than 0.15, the adhesion of the glass coating formed on the steel sheet surface deteriorates, and if it exceeds 1.1, defects occur in the glass coating. In particular, when the heating rate in the temperature rising stage is increased to 40 ° C / s or more, oxidation during soaking is promoted. Therefore, in order to manage the oxygen amount within a certain range, the degree of atmospheric oxidation is lowered. Or soaking time needs to be shortened.
[0029]
The heating method is not particularly limited. For a heating rate of about 40 to 100 ° C./second, a conventional radiant tube using normal radiant heat or a decarburization annealing equipment using a heating element is remodeled. For a heating rate of ° C./second or more, a method using a high energy heat source such as a new laser or plasma, induction heating, an electric heating device, or the like can be applied. Also, combining conventional radiant tubes using normal radiant heat and decarburization annealing equipment with heating elements using a new energy source such as laser and plasma, methods using induction heating, electric heating devices, etc. Is also effective.
[0030]
The soaking temperature is set in consideration of the adjustment of the primary recrystallized grain structure as disclosed in, for example, JP-A-2-182866. Usually, it is performed in the range of 770 to 900 ° C. It is also effective to increase the temperature of the soaking process by increasing the temperature after soaking for the purpose of grain adjustment, or increasing the soaking time by lowering the degree of oxidation of the atmosphere gas at the succeeding stage, after decarburizing before the soaking.
[0031]
As the nitriding treatment, there are a method of annealing in an atmosphere containing a nitriding gas such as ammonia, a method of adding a nitriding powder such as MnN into an annealing separator and performing it during finish annealing. In order to perform secondary recrystallization stably when the heating rate of decarburization annealing is increased, it is necessary to adjust the composition ratio of (Al, Si) N, and the amount of nitrogen after nitriding treatment is It is necessary that the mass ratio of N / Al is 0.67 or more with respect to the amount of Al.
[0032]
Thereafter, after applying an annealing separator mainly composed of magnesia, finish annealing is performed to preferentially grow {110} <001> oriented grains by secondary recrystallization.
[0033]
【Example】
<Example 1>
By weight, Si: 3.3%, C: 0.06%, acid-soluble Al: 0.020, 0.026, 0.031%, N: 0.008%, Mn: 0.1%, S : A slab containing 0.007% was heated at a temperature of 1150 ° C. and then hot-rolled to a thickness of 2.0 mm. Then, after annealing at 1120 ° C., after cold rolling to a thickness of 0.22 mm, after decarburizing and annealing at a temperature of 830 to 860 ° C. at a heating rate of 15 to 100 ° C./sec, an ammonia-containing atmosphere Was annealed at 0.02 to 0.03% of nitrogen in the steel sheet. Then, after applying an annealing separator mainly composed of MgO, finish annealing was performed. Table 1 shows the product characteristic values. With respect to the primary recrystallization texture, the value of I [111] / I [411] is 3 or less, the heating rate in the decarburization annealing process: HR is the amount of acid-soluble Al: HR ≧ −6250 with respect to [Al]% When [Al] +200 is satisfied, it can be seen that a high magnetic flux density of B8 of 1.92 T or more is obtained. In other words, when [Al] is increased, B8 for the same decarburization annealing rate is improved, and it can be seen that the region of the decarburization annealing heating rate at which high B8 can be obtained extends to the region of a small heating rate.
[0034]
[Table 1]

[0035]
<Example 2>
In mass%, Si: 3.3%, C: 0.05%, acid-soluble Al: 0.027, 0.031%, N: 0.007%, Cr: 0.1%, Sn: 0.05 %, Mn: 0.1%, S: 0.008% slab is heated at a temperature of 1150 ° C, then hot rolled to a thickness of 2.0 mm, and this hot rolled plate is annealed at 1120 ° C. Thereafter, it was cold-rolled to a thickness of 0.22 mm. The cold-rolled sheet was heated to 800 ° C. at a heating rate of 10 to 600 ° C./second, and then decarburized and annealed at 800 to 890 ° C. for 120 seconds and an atmospheric oxidation degree of 0.44. The oxygen content of the steel plate at this time was 1.9 to 2.1 g / m ² .
[0036]
Thereafter, annealing was performed in an ammonia-containing atmosphere at 750 ° C. for 30 seconds, and the nitrogen content in the steel sheet was adjusted to 0.023 to 0.029% by changing the ammonia content. Then, after apply | coating the annealing separation agent which has a magnesia as a main component, finish annealing was performed at 1200 degreeC for 20 hours.
These samples were subjected to tension coating treatment. The properties of the obtained product are shown in Table 2. From Table 2, the value of I [111] / I [411] for the primary recrystallization texture is 3 or less, the heating rate in the decarburization annealing process: HR is the amount of acid-soluble Al: [Al]% When HR ≧ −6250 [Al] +200 is satisfied, it can be seen that B8 has a high magnetic flux density of 1.92 T or more. In particular, it can be seen that when HR is 75 ° C./sec to 140 ° C./sec, B8 is particularly high, and that region expands to the lower limit side when [Al] increases.
[0037]
[Table 2]

[0038]
<Example 3>
In mass%, Si: 3.2%, Mn: 0.1%, C: 0.05%, S: 0.008%, acid-soluble Al: 0.024%, N: 0.008%, Sn: A 2.0 mm thick silicon steel hot rolled sheet containing 0.05% was cold rolled to a final sheet thickness of 0.22 mm. The cold-rolled sheet was heated to 840 ° C. at a heating rate of (1) 20 ° C./second (2) 100 ° C./second in a mixed gas of nitrogen and hydrogen with an oxidation degree of 0.33, and then annealed at 840 ° C. for 150 seconds to perform primary processing. Recrystallized. Thereafter, annealing was performed at 750 ° C. for 30 seconds in an ammonia-containing atmosphere, and the nitrogen content in the steel sheet was adjusted to 0.022 to 0.026% by changing the ammonia content.
[0039]
After applying an annealing separator mainly composed of magnesia to these steel plates, finish annealing was performed. The final annealing was performed at a heating rate of 15 ° C./hr in an atmosphere gas of N ₂ : 25% + H ₂ : 75% up to 1200 ° C., and the annealing was performed at 1200 ° C. by switching to H 2: 100% for 20 hours.
These samples were subjected to tension coating treatment. Table 3 shows the magnetic properties of the obtained products. Compared with Examples 1 and 2, since the annealing before cold rolling was not performed, the overall magnetic flux density was low, but the magnetic flux density improving effect of the present invention could be confirmed.
[0040]
[Table 3]

[0041]
<Example 4>
In mass%, Si: 3.2%, C: 0.05%, acid-soluble Al: 0.029%, N: 0.008%, Mn: 0.1%, S: 0.007%, contained The silicon steel slab was heated to 1100 ° C. to a thickness of 2.0 mm. This hot-rolled sheet was annealed at 1100 ° C. and cold-rolled to a final sheet thickness of 0.2 mm. Then, after heating to 850 degreeC with the heating rate of 100 degreeC / sec, it cooled to room temperature. After heating at a heating rate of 30 ° C./second, annealing at 830 ° C. for 90 seconds with an atmospheric gas having an oxidation degree of 0.12 to 0.72, annealing at 750 ° C. for 30 seconds in an ammonia-containing atmosphere, The nitrogen amount was 0.02 to 0.03%. Next, after applying an annealing separator mainly composed of MgO, finish annealing was performed at 1200 ° C. for 20 hours.
[0042]
Table 4 shows the product characteristics. From Table 4, when the atmosphere specified in the present invention falls outside the range of the oxidation degree exceeding 0.15 and 1.1 or less, and the oxygen amount after decarburization annealing is 2.3 g / m ² or less, the glass of the product It can be seen that the film properties are deteriorated.
[0043]
[Table 4]

[0044]
<Example 5>
In mass%, Si: 3.2%, C: 0.05%, acid-soluble Al: 0.024%, N: 0.007%, Cr: 0.1%, Sn: 0.05%, Mn: A silicon steel slab containing 0.1% and S: 0.008% was heated at 1150 ° C. and hot-rolled to a plate thickness of 2.3 mm. This hot-rolled sheet was annealed at 1120 ° C. and then cold-rolled to a thickness of 0.22 mm. After this cold-rolled sheet was heated to 800 ° C. at 100 ° C./sec, it was decarburized and annealed at 820 ° C. for 90 to 600 seconds with an atmospheric oxidation degree of 0.52, and the value of I {111} / I {411} was set to 2 The primary recrystallization texture was adjusted so that the inequality of claim 1 was established. Then, it annealed in ammonia containing atmosphere at 750 degreeC for 30 second, and the nitrogen content in a steel plate was 0.023-0.029%. After applying an annealing separator mainly composed of MgO, finish annealing was performed at 1200 ° C. for 20 hours.
[0045]
Table 5 shows product characteristic values. It can be seen that when the oxygen content of the steel sheet increases to 2.41 g / m ² , the magnetic properties are deteriorated.
[0046]
[Table 5]

[0047]
<Example 6>
In mass%, Si: 3.2%, C: 0.05%, acid-soluble Al: 0.024%, N: 0.007%, Cr: 0.1%, Sn: 0.05%, Mn: A silicon steel slab containing 0.1% and S: 0.008% was heated at 1150 ° C. and hot-rolled to a thickness of 2.3 mm. This hot-rolled sheet was annealed at 1120 ° C. and then cold-rolled to a thickness of 0.22 mm. The cold-rolled sheet was heated to 800 ° C. at 100 ° C./second, and then decarburized and annealed at 820 ° C. for 110 seconds at an atmospheric oxidation degree of 0.44. Texture: I {111} / I {411} had a value of 1.7 and a steel plate oxygen content of 1.9 g / m ² . Thereafter, annealing was performed in an ammonia-containing atmosphere at 750 ° C. for 30 seconds, and the nitrogen content in the steel sheet was set to 0.012 to 0.026% by changing the ammonia content. Then, after apply | coating the annealing separation agent which has a magnesia as a main component, finish annealing was performed at 1200 degreeC for 20 hours.
[0048]
Table 6 shows the characteristic values of the products. It can be seen that the magnetic flux density increases when the amount of nitrogen after nitriding is 0.017% or more ([N] / [Al] ≧ 0.67).
[0049]
[Table 6]

[0050]
<Example 7>
In mass%, Si: 3.3%, C: 0.06%, acid-soluble Al: 0.020, 0.026, 0.031%, N: 0.008%, Mn: 0.1%, S : A slab containing 0.007% was heated at a temperature of 1150 ° C. and then hot-rolled to a thickness of 2.0 mm. The hot rolled sheet was annealed at 1120 ° C. in the front stage and 900 ° C. in the back stage, and then cold-rolled to a thickness of 0.15 mm, and then the heating rate of decarburization annealing was set at 15-100 ° C./second, at a temperature of 810-860 ° C. After decarburization annealing, the steel was annealed in an ammonia-containing atmosphere so that the nitrogen in the steel sheet was 0.02 to 0.03%. Then, after applying an annealing separator mainly composed of magnesia, finish annealing was performed.
Table 7 shows the product characteristic values. Heating rate in the decarburization annealing process: When HR is HR ≧ −6250 [Al] +200 with respect to the amount of acid-soluble Al: [Al]%, a high magnetic flux density with B8 of 1.92 T or more can be obtained. I understand that
[0051]
[Table 7]

[0052]
<Example 8>
In mass%, Si: 3.3%, C: 0.05%, acid-soluble Al: 0.025%, 0.035%, N: 0.007%, Cr: 0.1%, Sn: 0.00. A slab containing 05%, Mn: 0.1%, S: 0.008% was heated at a temperature of 1150 ° C, and then hot rolled to a thickness of 2.3 mm. The hot-rolled sheet was annealed at 1120 ° C. And then cold rolled to a thickness of 0.18 mm. This cold-rolled sheet was heated to 800 ° C. at a heating rate of 5 to 600 ° C./second, and then decarburized and annealed at 800 to 890 ° C. for 120 seconds with an atmospheric oxidation degree of 0.52, and the primary recrystallization texture was shown in FIG. It adjusted to the area | region where high B8 shown by (4) was obtained. Thereafter, annealing was performed at 750 ° C. for 30 seconds in an ammonia-containing atmosphere, and the nitrogen content in the steel sheet was adjusted to 0.025 to 0.035% by changing the ammonia content. Then, after apply | coating the annealing separation agent which has a magnesia as a main component, finish annealing was performed at 1200 degreeC for 20 hours.
The characteristics of the obtained product are shown in Table 8. From Table 8, when the heating rate in the decarburization annealing process: HR is HR ≧ −6250 [Al] +200 with respect to the amount of acid-soluble Al: [Al]%, B8 has a high magnetic flux of 1.92 T or more. It can be seen that the density is obtained. In particular, when [Al] is increased, the high B8 effect by the cold rolling method is more prominent, and even if the decarburization annealing heating rate is low, the high B8 effect is obtained and a higher B8 is obtained. Can do.
[0053]
[Table 8]

[0054]
【The invention's effect】
According to the present invention, based on a method for producing a grain-oriented electrical steel sheet by low-temperature slab heating without problems caused by conventional high-temperature slab heating, primary recrystallization structure, decarburization annealing conditions for acid-soluble Al, surface oxide layer and nitriding By defining the amount, a grain-oriented electrical steel sheet having high magnetic flux density and excellent magnetic properties can be produced industrially and stably. In particular, in a manufacturing method based on the assumption of a single cold rolling method, by defining the decarburization annealing conditions and nitriding amount for acid-soluble Al, a thin grain-oriented electrical steel sheet with excellent magnetic properties with high magnetic flux density is industrially produced. Can be manufactured stably. As a result, it is possible to obtain a grain-oriented electrical steel sheet that has less load on hot rolling, omits intermediate annealing, and is cheaper and more excellent in iron loss than in the past.
[Brief description of the drawings]
FIG. 1 is a graph showing the influence of acid-soluble Al and decarburization annealing heating rate on the magnetic flux density (B8) of a product.
FIG. 2 is a diagram showing the influence of the rapid heating completion temperature of decarburization annealing on the magnetic flux density.
FIG. 3 is a diagram showing the influence of the rapid heating start temperature of decarburization annealing on the magnetic flux density.
FIG. 4 is a diagram showing the influence of the cold rolling reduction ratio on the magnetic flux density.

Claims

In mass, Si: 0.8 to 4.8%, C: 0.085% or less, acid-soluble Al: 0.01 to 0.065%, N: 0.012% or less, or further if necessary The steel containing 1 or 2 types of Sn: 0.02-0.15%, Cr: 0.03-0.2%, and the balance Fe and unavoidable impurities are heated at a temperature of 1280 ° C or lower After that, it is formed into a hot-rolled sheet by hot rolling, and then the final sheet thickness is obtained by cold rolling with a rolling reduction of more than 90% at least once with intermediate or intermediate annealing. After decarburization annealing, magnesia is the main component. In the method of manufacturing a grain-oriented electrical steel sheet that is applied with an annealing separator and is subjected to finish annealing, the steel sheet temperature is 600 ° C. in the temperature raising process of the decarburization annealing process corresponding to the amount of acid-soluble Al: [Al]%. Heating rate from the following region to a predetermined temperature within a range of 750 to 900 ° C .: HR By adjusting HR ≧ −6250 [Al] +200 per second, the ratio of I [111] / I [411] in the texture after decarburization annealing is adjusted to 1.7 or more and 3 or less, and then nitriding A method for producing a grain-oriented electrical steel sheet, comprising:

The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein the hot-rolled sheet is annealed in a temperature range of 900 to 1200 ° C for 30 seconds to 30 minutes.

In the decarburization annealing step, the oxygen content of the steel sheet is 2.3 g within a temperature range of 770 ° C. to 900 ° C. and an atmosphere gas oxidation degree (PH ₂ O / PH ₂ ) of more than 0.15 and 1.1 or less. The method for producing a grain-oriented electrical steel sheet according to claim 1 or 2 , wherein the annealing is performed for a time such that / m ² or less.

Nitriding is performed so that the amount of nitrogen: [N] satisfies [N] / [Al] ≧ 0.67 according to the amount of acid-soluble Al in the steel sheet: [Al]. The manufacturing method of the grain-oriented electrical steel sheet according to any one of claims 1 to 3 .