JP2004211145A

JP2004211145A - Method for producing low core loss grain-oriented magnetic steel sheet and method for finish-annealing the same

Info

Publication number: JP2004211145A
Application number: JP2002380923A
Authority: JP
Inventors: Seiji Okabe; 誠司岡部; Minoru Takashima; 稔高島; Mineo Muraki; 峰男村木
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 2002-12-27
Filing date: 2002-12-27
Publication date: 2004-07-29
Anticipated expiration: 2022-12-27
Also published as: JP4345302B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a grain-oriented magnetic steel sheet and a method for finish-annealing the same, with which a core loss is reduced by flattening the surface of the steel sheet. <P>SOLUTION: In the method for producing the grain-oriented magnetic steel sheet, prescribed annealing and rolling are applied, annealing parting agent is coated, and the finish-annealing is applied to a steel slab containing 2.0-7.0 mass% Si, the annealing parting agent has a composition containing metallic oxide etc. in which total of magnesia has presence ratio of ≥20 mass%, and the metallic chloride etc., at the ratio in which the total of chlorine, bromine, and iodine is 0.1-10 parts by mass to the 100 parts by mass of the metallic oxide etc. The finish-annealing is performed in an atmosphere having 0-25 vol.% low hydrogen ratio in a first temperature range raising the temperature to a specific temperature and is performed under atmosphere having > 25 vol.% high hydrogen ratio in a second temperature range raising the temperature to not lower than the specific temperature, and soaking and holding the temperature. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は主に電力用トランスの鉄心として用いられる、低鉄損の方向性電磁鋼板の製造方法および仕上焼鈍方法に関する。特にその表面にフォルステライト等の酸化物被膜を剥離しやすい形態で適度に形成させた後に剥離させることによって、低鉄損化を図る。
【０００２】
【従来の技術】
Ｓｉを含有し、かつ結晶方位が（１１０）［００１］方位や（１００）［００１］方位に配向した方向性電磁鋼板は、優れた軟磁気特性を有することから、各種鉄心材料として広く用いられている。電磁鋼板に要求される特性としては、一般に５０Ｈｚの周波数で１．７Ｔに磁化させた場合の損失である、Ｗ_{１７／５０}値（Ｗ／ｋｇ）で表わされる、鉄損が低いこと及び軟磁性材料として保磁力が小さいことが重要である。
【０００３】
この鉄損を低減するには、渦電流損（Ｗｅ）およびヒステリシス損（Ｗｈ）を低下することが有効である。まず、渦電流損を低下するには、Ｓｉを含有させて電気抵抗を高める方法、鋼板板厚を低減する方法、さらに結晶粒径を低減する方法等があり、一方ヒステリシス損を低下するには、圧延方向に結晶粒の＜１００＞軸を高度に揃える方法が知られている。
【０００４】
このうちＳｉを過度に含有させる方法は、飽和磁束密度の低下を招いて鉄心のサイズ拡大の原因になる不利があり、また鋼板板厚を低減する方法も極端な製造コストの増大をもたらす不利があり、いずれも鉄損の低減には限界があった。
【０００５】
一方、結晶方位を揃える方法では、磁束密度Ｂ_８にして１．９６〜１．９７Ｔ程度の値の製品を得ることは可能であるが、これ以上の改善の余地は少なくなっている。
【０００６】
さらに、プラズマジェットやレーザー光を照射して鋼板表面に局所的に歪を導入したり、鋼板表面に溝を形成する等の方法によって人工的に磁区幅を細分化し鉄損を低減する技術が開発され、大幅な鉄損低減効果を得た。しかし、この技術による鉄損低減効果にも限界があった。
【０００７】
これらの技術とは別に、特許文献１には、鋼板地鉄表面と非金属被膜との界面の粗度を低減し、つまり地鉄表面を平滑化すること、さらに張力付与処理を行うことで材料の鉄損が大幅に低減することが報告されている。
【０００８】
【特許文献１】
特公昭５２−２４４９９号公報
【０００９】
ここで、方向性珪素鋼の二次再結晶焼鈍時に通常用いられる、ＭｇＯを主とする焼鈍分離剤は、焼鈍後の鋼板表面に主にフォルステライトからなる緻密な被膜を多量に形成するため、鋼板地鉄表面の粗さが低減されない上、さらなる鏡面を得るための鏡面化研磨やサーマルエッチにも不都合である。
【００１０】
このフォルステライト被膜の生成を抑制する方法として、例えば特許文献２には、ＭｇＯにアルカリ又はアルカリ土類金属の塩化物を２〜４０質量部添加した焼鈍分離剤を適用する方法が提案されている。しかし、これに記載された技術はフォルステライト被膜を抑制することに主眼が置かれており、得られる鋼板の磁気特性にはさらに改善の余地があった。
【００１１】
【特許文献２】
特開昭６４−６２４７６号公報
【００１２】
また、特許文献３には焼鈍分離剤としてアルミナを用いてフォルステライト被膜の生成を抑制する方法が提案されている。しかし、アルミナを焼鈍分離剤の主剤として用いた場合は、鋼中に含まれる硫化物、セレン化物、窒化物といった二次再結晶を生じさせるために含有しているインヒビターの純化が不十分になるという問題があった。また、通常のフォルステライト被膜ほど多量ではないものの、ＳｉやＡｌを含んだ若干の酸化物が表層に形成されて、完全に平滑な表面にはなりにくいという問題があった。
【００１３】
【特許文献３】
特開平５−１５６３６２号公報
【００１４】
これらの問題を解決するため、特許文献４には焼鈍分離剤に塩化物の平衡解離分圧に応じて雰囲気中の水素比率を変える技術が提案されている。この技術によれば、例えばＭｇＣ１_２を添加した場合は水素比率を０％に、ＡｌＣ１_３を添加した場合は水素比率を０〜２５％に、ＢｉＣｌ_２を添加した場合は水素比率を０〜１００％にすることが好適とされている。しかし、この技術を適用した鋼板でもさらなる鉄損低減の余地があった。
【００１５】
【特許文献４】
特開平５−２０４３９３号公報
【００１６】
【発明が解決しようとする課題】
そこで、この発明は、鋼板地鉄表面を平滑化して鉄損を低減する、方向性電磁鋼板の製造方法および仕上焼鈍方法を提供することを目的とする。
【００１７】
【課題を解決するための手段】
発明者らは、塩化物等のハロゲン化物を添加した焼鈍分離剤を用いて鋼板表面を平滑化するための技術について鋭意検討を行った結果、従来法のようにフォルステライト被膜の形成を抑制するのではなく、フォルステライト被膜を剥離しやすい形態で適度に形成させることで、鋼板の表面平滑化を有利に進行させ得ることを見出した。
【００１８】
また、焼鈍分離剤中に含有する金属酸化物および／または金属水酸化物に占めるマグネシウムの酸化物および／または水酸化物の存在割合と、仕上焼鈍中の温度域における水素比率の適正化を図ることによって、適度なフォルステライト被膜が形成できること、および、焼鈍分離剤中に、金属塩化物、金属臭化物および金属ヨウ化物のうちから選ばれる１種または２種以上を適量含有させることによって、フォルステライト被膜の形成を促進するとともにフォルステライト被膜を剥離しやすくできることを見いだし、本発明を完成させた。
【００１９】
本発明の要旨構成は次のとおりである。
（１）Ｓｉ：２．０〜７．０質量％を含有する鋼スラブに、焼鈍および圧延を施して最終板厚の冷間圧延板とした後、一次再結晶焼鈍を施し、焼鈍分離剤を塗布し、二次再結晶を生じさせるための仕上焼鈍を施す方向性電磁鋼板の製造方法において、
焼鈍分離剤は、マグネシウムの酸化物および／または水酸化物が合計で２０質量％以上の存在割合である金属酸化物および／または金属水酸化物と、金属塩化物、金属臭化物および金属ヨウ化物のうちから選ばれる１種または２種以上とを、前者１００質量部に対し後者における塩素、臭素およびヨウ素の合計で０．１〜１０質量部の割合で含有させた組成になり、
仕上焼鈍は、少なくとも９５０℃以上の特定温度まで昇温する第１温度域では０〜２５体積％の低水素比率とした雰囲気で行い、特定温度以上に昇温して均熱保持する第２温度域では２５体積％超えの高水素比率とした雰囲気で行うことを特徴とする低鉄損方向性電磁鋼板の製造方法。
【００２０】
（２）金属塩化物、金属臭化物および金属ヨウ化物の金属イオンが、Ｃｕ、Ｉｎ、ＳｎおよびＳｂイオンのうちから選ばれた１種又は２種以上の金属イオンであることを特徴とする上記（１）記載の低鉄損方向性電磁鋼板の製造方法。
【００２１】
（３）金属塩化物、金属臭化物および金属ヨウ化物の金属イオンが、Ｚｎ、Ａｇ、ＰｂおよびＢｉイオンのうちから選ばれた１種又は２種以上の金属イオンであることを特徴とする上記（１）記載の低鉄損方向性電磁鋼板の製造方法。
【００２２】
（４）Ｓｉ：２．０〜７．０質量％を含有する鋼板に、二次再結晶を生じさせて方向性電磁鋼板を製造するための仕上焼鈍を施す方法において、
該鋼板に、マグネシウムの酸化物および／または水酸化物が合計で２０質量％以上の存在割合である金属酸化物および／または金属水酸化物と、金属塩化物、金属臭化物および金属ヨウ化物のうちから選ばれる１種または２種以上とを、前者１００質量部に対し後者における塩素、臭素およびヨウ素の合計で０．１〜１０質量部の割合で含有させた組成になる焼鈍分離剤を塗布してから、仕上焼鈍を、少なくとも９５０℃以上の特定温度まで昇温する第１温度領域では０〜２５体積％の低水素比率とした雰囲気で行い、特定温度以上に昇温して均熱保持する第２温度領域では２５体積％超えの高水素比率とした雰囲気で行うことを特徴とする低鉄損方向性電磁鋼板の仕上焼鈍方法。
【００２３】
【発明の実施の形態】
以下、この発明について具体的に説明する。まず、この発明の電磁鋼板について、仕上焼鈍前までの製造方法は公知の方法が適用できる。その望ましい構成について説明する。
【００２４】
まず、この発明で使用される鋼板の成分組成としては、Ｓｉを２．０〜７．Ｏ質量％含有することが必須である。すなわち、Ｓｉは、製品の電気抵抗を高め鉄損を低減するのに有効な成分であるが、７．Ｏ質量％を超えると硬さが高くなり製造や加工が困難になり、また、飽和磁束密度の低下も生じる。一方、２．Ｏ質量％未満であると、２次再結晶焼鈍中に変態を生じて安定した二次再結晶組織が得られないため、下限を２．Ｏ質量％とする。
【００２５】
また、インヒビター成分として、Ａｌを初期鋼中に０．０１質量％以上含有することにより、結晶配向性を向上することができる。なお、Ａｌを添加する場合は、０．０６質量％を超えると、再び結晶配向性の劣化が生じるので０．０６質量％以下とすることが好ましい。窒素も同様の作用があり、上限はふくれ欠陥の発生抑制のために２００質量ｐｐｍに定めるとよく、その下限は特に規定しないが、１０質量ｐｐｍ未満まで工業的に低下させるのは経済的に困難になることから、その下限を１０質量ｐｐｍとすることが好ましい。
【００２６】
ここで、１次再結晶焼鈍後に、後述する増窒素処理を行う工程を付加することが、スラブ加熱温度の制約から解放されて操業の自由度が増すという観点で有利であるが、この増窒素処理を行わない場合は、初期鋼中にＳｅ＋Ｓの和で０．０１〜０．０６質量％を含有することが推奨される。加えて、これらをＭｎ化合物として析出させるために、０．０１〜０．２質量％のＭｎを含有させることが望ましい。それぞれ少なすぎると、二次再結晶を生じるための析出物が過小となり、また多すぎると熱間圧延前の固溶が困難となる傾向があるため、それぞれの下限および上限の範囲内で添加することが好ましい。
【００２７】
一方、増窒素処理を行う場合には、Ｍｎ，ＳｅおよびＳは必ずしも必要ではないが、鋼の延性改善等の目的で適宜添加してもよい。この場合のＭｎ，ＳｅおよびＳの含有量もまた、上記と同様の理由から上記の好適範囲と同じにすることが好ましい。
【００２８】
さらに、鋼中には、上記の元素の他に方向性電磁鋼板の製造に適する添加成分である、Ｂ、Ｂｉ、Ｓｂ、Ｍｏ、Ｔｅ、Ｓｎ、Ｐ、Ｇｅ、Ａｓ、Ｎｂ、Ｎｉ、Ｃｒ、Ｔｉ、Ｃｕ、Ｐｂ、ＺｎおよびＩｎから選ばれる元素を単独、または複合で０．０００５〜２．Ｏ質量％含有させることが好ましい。この含有量が、０．０００５質量％未満では効果が顕著に認められなくなり、一方、２．Ｏ質量％を超えると、磁束密度の低下を生じるおそれがあるからである。また、初期鋼中には再結晶集合組織を制御して磁気特性を向上させる目的で、０．００５〜０．８質量％のＣを添加することもできる。
【００２９】
なお、Ｃ、Ｓ、ＳｅおよびＮなどの元素はいずれも、磁気特性上有害な作用があり、特に鉄損を劣化させることから、製品板においてはそれぞれＣ：０．００３質量％以下、ＳおよびＳｅ：各々０．００２質量％以下ならびにＮ：０．００２質量％以下に低減することが好ましい。とりわけ、この発明で所期する特性を達成するためには、析出物として存在する鋼中炭化物の量を３０質量ｐｐｍ未満とすることが極めて重要である。
【００３０】
次に、この発明の方向性電磁鋼板の製造方法について詳細に説明する。すなわち、所定の成分に調整された鋼塊やスラブから、公知の方法により熱間圧延、次いで冷間または温間圧延により最終板厚とする。連続熱延法やシートバーキャスト法、コイルキャスト法で得た素材にも、この発明は適用可能である。その後、１次再結晶焼鈍、そして必要に応じて増窒素処理を行う。
【００３１】
ここで、増窒素処理とは、ＡｌＮとして用いられるインヒビターを熱間圧延時に固溶させるための高温加熱処理を省略することを日的として行う処理である。具体的には、一次再結晶後の鋼板をアンモニアを含む雰囲気中で加熱通板することなどにより行われる。
【００３２】
次いで、マグネシア、カルシア、アルミナ、フォルステライトなどの酸化物を主成分とする焼鈍分離剤を鋼板に付着させる。マグネシアやカルシアなどは水和して水酸化物となっていてもよい。ここで焼鈍分離剤中に含有する金属酸化物および／または金属水酸化物に占めるマグネシア（マグネシウムの酸化物および／または水酸化物）が合計で２０〜１００質量％の存在割合であるの存在割合が質量比で２０〜１００％であることが必要である。これは仕上焼鈍中に適度のフォルステライト被膜を鋼板表面に形成するのに必要なマグネシウムを供給するためである。本発明では、一旦フォルステライトを形成させてこれを剥離させることにより表面を平滑化させる手法を用いるが、マグネシアの存在割合が２０％未満では、表面平滑化に必要な適度なフォルステライト被膜の形成が困難になるので、その下限を２０質量％とした。なお、金属酸化物および／または金属水酸化物がマグネシア単独であってもよいため、マグネシアの存在割合の上限は特に設けない。
【００３３】
焼鈍分離剤の付着量の目安は概ね２〜５０ｇ／ｍ^２であり、水スラリーにして塗布・乾燥しても、静電塗布してもよく、その付着方法に制限はない。
【００３４】
また、本発明では、焼鈍分離剤が、上記金属酸化物および／または金属水酸化物に加えて、金属塩化物、金属臭化物および金属ヨウ化物のうちから選ばれる１種または２種以上を適量含有する組成になることが必要である。これによって、仕上焼鈍にて焼鈍分離剤中のマグネシアと地鉄表面のＳｉ含有酸化物との反応によって生じるフォルステライト被膜が剥離しやすい形態にすることができ、仕上焼鈍完了時に平滑な地鉄表面が得られるようになる。
【００３５】
ここで金属塩化物、金属臭化物および金属ヨウ化物の金属イオンとしては、例えば、アルカリ金属やアルカリ土類金属、さらにＡｌ、Ｔｉ、Ｖ、Ｃｒ、Ｍｎ、Ｆｅ、Ｃｏ、Ｎｉ、Ｃｕ、Ｚｎ、Ａｇ、Ｉｎ、Ｓｎ、Ｓｂ、Ｐｂ、Ｂｉ等の金属イオンが挙げられる。これらの金属イオンのうち、特にＣｕ、Ｉｎ、ＳｎおよびＳｂイオンは、仕上焼鈍中に地鉄内にその一部が取り込まれ、インヒビターとして作用し、結晶方位のゴス方位への集積度を高め、磁気特性を向上させる効果があるため好適である。また、Ｚｎ、Ａｇ、ＰｂおよびＢｉイオンは、地鉄表面の平滑性を向上させる効果が大きく、鉄損を低減するためには好適である。ここで、金属の塩化物、臭化物、ヨウ化物としては、金属とハロゲン化物からなる化合物以外にも、例えばＳｂＯＣｌのように酸素等の元素を含む化合物や、ＳｎＣ１_２・２Ｈ_２Ｏのように結合水が含まれている化合物であってもよい。
【００３６】
これらの金属の塩化物、臭化物およびヨウ化物は融点が低く、仕上焼鈍における昇温初期の比較的低い温度から融解し、焼鈍分離剤中のマグネシアと地鉄の表面を濡らし、両者が反応してフォルステライト被膜を形成するのを促進する。このように塩化物等の作用によって低温から形成されたフォルステライト被膜は、地鉄との界面が平坦に形成され、従来の方向性珪素鋼板のフォルステライト被膜に見られるような、いわゆるアンカーが発達しない。そのため、仕上焼鈍の冷却過程で鋼板との熱膨張の差によって容易に剥離するようになり、剥離後の地鉄表面は平滑になる。また、一度形成されたフオルステライト被膜は仕上焼鈍中には鋼板表面に付着しているため、高温域での不要な追加酸化を抑制し、サーマルエッチングによる表面の平滑化を助ける効果もある。また、鋼中にインヒビター成分としてＳやＳｅが含有されている場合、これらの元素を鋼中から表面に引き出す作用があり、極めて有用である。
【００３７】
このように仕上焼鈍における、加熱（昇温）や加熱温度保持時にフォルステライト被膜を剥離しやすい形態で形成させ、冷却時にフォルステライト被膜を剥離させるという本発明の技術思想は、フォルステライトの形成を阻害・抑制させて表面を平滑化するという従来の技術思想とは大きく異なっている。
【００３８】
また、本発明では、焼鈍分離剤中に含有させる、金属塩化物、金属臭化物および金属ヨウ化物の含有量の適正範囲は、金属酸化物および／または金属水酸化物１００質量部に対し、塩素、臭素およびヨウ素の合計で０．１〜１０質量部の割合になることが必要である。金属塩化物、金属臭化物および金属ヨウ化物の含有量の適正範囲が、前記割合にして０．１質量部よりも少ないと、剥離しやすいフォルステライト被膜の形成促進効果が得られないからであり、また、１０質量部よりも多いと、フォルステライト形成反応が過剰になり、地鉄内部にフォルステライトか食い込むように形成され、冷却中の剥離を阻害したり、磁気特性を劣化させるからである。
【００３９】
その他、焼鈍分離剤中には、公知の硫化物、水酸化物、ほう酸塩、硝酸塩、燐酸塩、炭酸塩および／または硫酸塩をさらに加えて、二次再結晶の制御を行ってもよい。
【００４０】
次にこの焼鈍分離剤を付着させた鋼板をコイル状、または積層した状態にして仕上焼鈍を行い、二次再結晶を生じさせるが、本発明では、この仕上げ焼鈍における雰囲気中の水素比率を制御することが地鉄表面の平滑化を図るのに重要である。
【００４１】
まず、仕上焼鈍にて、常温から少なくとも９５０℃以上の特定温度まで昇温する第１温度域では、水素比率（分圧の比率）を０〜２５体積％の低水素比率とした雰囲気にする必要がある。水素比率が２５％を超えるとフォルステライトの低温からの形成を阻害したり、地鉄との界面との平坦性が損なわれるなどにより、仕上焼鈍後の地鉄表面の平滑度が劣化したり、フォルステライト被膜が地鉄上に残留するといった問題が生じるからである。前記水素比率の下限は０％であってもよく、特に規定しないが、最も好適な低水素比率は０〜５％の範囲である。なお、前記雰囲気の水素以外の残部は、窒素およびアルゴンの一方または両方であることが好適である。
【００４２】
一方、仕上焼鈍にて、特定温度以上（例えば９５０℃以上）に昇温して均熱保持する第２温度域では、フォルステライトと地鉄の界面が平滑化される、いわゆるサーマルエッチングが効果的に生じる。よって、特定温度以上で雰囲気中の水素比率を２５体積％超えの高水素比率とした雰囲気に切り換えることで、このこのサーマルエッチングの効果が促進され、仕上焼鈍後の磁気特性の改善に著しい効果がある。その理由は定かではないが、鋼板表面に残留したフォルステライト以外の酸化物の安定性を下げたり、ハロゲン化物が分解して生じた金属元素が地鉄表面に作用するためではないかと考えられる。
【００４３】
また、インヒビター成分としてＳやＳｅを使用している場合には、これらの成分を鋼中から除外する、いわゆる純化が促進される効果もある。水素比率が２５％以下の場合は、表面の平滑度が不十分になったり、ＳやＳｅの純化が不良になるなどの問題が生じる。高水素比率の上限は特に制限はなく、１００体積％であってもよく、好適には高水素比率は７０〜１００％とする。
【００４４】
このように水素比率を高めた雰囲気で、特定温度以上（例えば９５０℃以上）、好ましくは１１００〜１２５０℃まで加熱（昇温）して均熱保持することで、表面平滑度が改善される。
【００４５】
鋼板の冷却に際しては、２００℃以下の低温になるまで、非酸化性の雰囲気にして鋼板表面の酸化（テンパーカラー）を抑制することが好ましい。
【００４６】
なお、必要に応じて二次再結晶後の鋼板を、さらに電解研磨，化学研磨，物理的研磨，サーマルエッチ等で平滑化処理することも可能である。あるいは、水溶性ハロゲン化合物中で電解する処理（結晶方位強調処理）、すなわち結晶板面方位に応じて電解速度が異なることを利用した処理も有利に適合する。
【００４７】
なお、この発明は、従来の磁区細分化技術との併用が可能であり、併用により加算的以上の相乗効果が得られる。ここでいう磁区細分化技術とは、例えば製品の鋼板表面にレーザーやプラズマジェットを照射して局所的に歪領域を設ける方法、鋼板表面に溝を設ける方法、鋼板表面の組織もしくは組成を被膜も含めて局所的に変更する方法などが挙げられ、製造に際しての手法も突起ロールやエッチング法など従来公知のものが適用できる。その中でも、二次再結晶後の鋼板に電解エッチングにより点状または線状の溝領域を形成する方法は、鋼板に歪を与えず、効果的な断面形状の溝を効率よく付与できるために、推奨される。
【００４８】
さらに、鋼板に張力被膜を設けることにより、僅かな張力で効果的に鉄損を改善できる。方向性電磁鋼板は、通常積層して使用され、その際に層間の導通がないことが求められるため、上記の張力被膜は絶縁材料としての機能を持たせることが可能であり、また別途絶縁被膜を設けても良い。
【００４９】
なお、鋼板の厚みは特に規定しないが、渦電流損のうち古典的渦電流損は板厚の関数であるから、要求される鉄損に応じてコストと勘案の上、板厚を定めればよく、通常は０．１〜０．３５ｍｍの範囲である。
【００５０】
【実施例】
実施例１
Ｃ：０．０５質量％、Ｓｉ：３．２質量％、Ｍｎ：０．０６質量％、Ｓ：０．０２質量％、Ｓｅ：０．００１質量％、Ａｌ：０．０２質量％、Ｎ：８Ｏ質量ｐｐｍ、Ｓｎ：０．３質量％およびＣｕ：０．２質量％を含み、残部はＦｅおよび不可避的不純物からなる鋼スラブを１２５０℃に加熱したのち、熱間圧延を施し２．Ｏｍｍの熱延板とし、温間圧延により板厚：０．２１ｍｍの鋼板とし、その後脱炭を兼ねた１次再結晶焼鈍を施した。そして、この鋼板に、アルミナとマグネシアを各種の比率で混合した焼鈍分離剤に、さらにＭｇＣ１_２・６Ｈ_２Ｏを、アルミナとマグネシアの合計で１００質量部に対し、塩素（Ｃｌ）の質量で１質量部の割合で添加したものを、鋼板表面に静電塗布した。このときの焼鈍分離剤の付着量（両面で、以下同様とする。）は１４ｇ／ｍ^２であった。
【００５１】
次に、焼鈍分離剤を塗布したそれぞれの鋼板を、外径１．５ｍのコイル状に巻き取ったのち、８００℃までを窒素雰囲気中で平均５０℃／ｈで昇温し、８００℃から９５０℃を窒素雰囲気中にて平均４．５℃／ｈで昇温し、その後１２００℃まで平均１４℃／ｈで水素雰囲気にて昇温し、引き続き１２００℃で６時間の純化焼鈍を兼ねた二次再結晶焼鈍を行ったのち放冷して方向性電磁鋼帯を得た。
【００５２】
かくして得られた鋼帯を水洗およびリン酸酸洗によって表面を洗浄し、さらに６ＭＰａの張力を加えながら８２０℃で２０秒間保持する平坦化焼鈍を、３体積％の水素を含む窒素雰囲気中での連続焼鈍によって行った。
こうして得られた鋼帯から磁気測定用の試料を取り、歪取り焼鈍を行ってから、１．７Ｔ、５０Ｈｚでの履歴損をエプスタイン枠を使った直流磁化測定によって求めた。酸素目付量（両面で、以下同様とする。）と履歴損の測定結果を表１に示すが、マグネシアの存在比率が２０％以上で平滑な地鉄表面が得られ、履歴損も低減されている。
【００５３】
【表１】

【００５４】
実施例２
Ｃ：０．０６質量％、Ｓｉ：３．２質量％、Ｍｎ：０．０６質量％，Ａｌ：０．０２質量％，Ｎ：８０質量ｐｐｍ，Ｓｂ：０．１質量％を含み、残部はＦｅおよび不可避的不純物からなる鋼スラブを、誘導加熱により１４００℃に加熱したのち、熱間圧延を施し２．Ｏｍｍの熱延板とし、熱延板焼鈍を施してから中間焼鈍をはさむ冷間圧延により板厚：０．２１ｍｍの鋼板とした。その後、脱炭焼鈍を兼ねた１次再結晶焼鈍を施した。
そして、この鋼板に各種の金属の塩化物、臭化物またはヨウ化物を添加したマグネシアを、水スラリーとして鋼板表面に塗布し、大気中２２０℃で焼付け乾燥した。このときの焼鈍分離剤の付着量は９．５ｇ／ｍ^２であった。
【００５５】
次に、このコイルを８００℃までをＮ_２雰囲気中で平均５０℃毎時で昇温し、８００℃から９００℃をアルゴン雰囲気中で平均４．５℃／ｈで昇温し、９００℃から１１５０℃を平均２０℃／ｈでアルゴン雰囲気にて昇温し、その後水素雰囲気中で１１５０℃で６時間の二次再結晶焼鈍を行ったのち、方向性電磁鋼帯を得た。
【００５６】
かくして得られた鋼帯を水洗およびリン酸酸洗によって表面を洗浄し、さら９ＭＰａの張力を加えながら８ｌＯ℃で３０ｓ保持する平坦化焼鈍を、２％の水素を含む窒素雰囲気中での連続焼鈍によって行った。
こうして得られた鋼帯から磁気測定用の試料を取り、歪取り焼鈍を行ってから、１．７Ｔ、５０Ｈｚでの履歴損と、８００Ａ／ｍにおける磁束密度Ｂ_８とをエプスタイン枠を使った直流磁化測定によって求めた。
【００５７】
このようにして得られた方向性電磁鋼板の表面形態と履歴損を表２に示す。焼鈍分離剤中に、本発明の範囲のハロゲン化物を添加した発明例はいずれも、平滑化された地鉄表面と良好な磁気特性が得られる。特にＣｕ、Ｉｎ、ＳｎまたはＳｂのハロゲン化物を添加した発明例は、Ｂ_８が高く、Ｚｎ、Ａｇ、ＰｂまたはＢｉのハロゲン化物を添加した発明例は、酸素目付量と履歴損が小さく、特に好適である。
【００５８】
【表２】

【００５９】
実施例３
Ｃ：０．０６５質量％、Ｓｉ：３．４質量％、Ｍｎ：０．１質量％、Ａｌ：０．０１質量％、Ｎ：７０質量ｐｐｍ、Ｓｅ：０．０１４質量％およびＳｂ：Ｏ．０５質量％を含み、残部はＦｅおよび不可避的不純物からなる鋼スラブを、誘導加熱により１４００℃に加熱したのち、熱間圧延を施し２．０ｍｍの熱延板とし、熱延板焼鈍を施してから中間焼鈍をはさむ温間圧延により板厚：０．２２ｍｍの鋼板とした。その後、脱炭焼鈍を兼ねた１次再結晶焼鈍を施した。
そして、この鋼板に、マグネシア１００質量部に対してＳｎＣ１_２を塩素質量で２質量部添加した組成になる焼鈍分離剤を、水スラリーとして鋼板表面に塗布し、大気中２００℃で焼付け乾燥した。このときの焼鈍分離剤の付着量は１５ｇ／ｍ^２であった。
【００６０】
次に、このコイルを、窒素雰囲気中で平均５０℃毎時で７００℃まで昇温し、７００℃から８１０℃までを低水素比率の雰囲気Ａで平均４０℃毎時で昇温し、９００℃を平均８℃／ｈで昇温し、９００℃から１１５０℃までを平均１２℃／ｈで昇温して６時間均熱保持する二次再結晶焼鈍を行ったのち、方向性電磁鋼帯を得た。ここで、８００℃以上での特定の温度Ｘで高水素比率の雰囲気Ｂに切り替えた。この雰囲気ＡおよびＢは、水素や窒素の単独または混合の雰囲気で、この水素比率を切り替える特定温度Ｘを各種変更した。焼鈍温度と雰囲気の概要を図１に示す。
【００６１】
かくして得られた鋼帯を水洗およびリン酸酸洗によって表面を洗浄し、さらに９ＭＰａの張力を加えながら８１０℃で３０秒間保持する平坦化焼鈍を水素を２％含む窒素雰囲気中での連続焼鈍によっておこなった。
こうして得られた鋼帯から磁気測定用の試料を取り、歪取り焼鈍を行ってから、１．７Ｔ、５０Ｈｚでの履歴損とをエプスタイン枠を使った直流磁化測定によって求めた。
このようにして得られた方向性電磁鋼板の表面形態と履歴損を表３に示す。本発明の雰囲気中の水素比率で、特定温度を９５０℃以上（表３では具体的には９５０〜１１００℃の範囲）にした場合に、地鉄表面の酸素目付け量の低減と低履歴損が得られる。
【００６２】
【表３】

【００６３】
【発明の効果】
この発明によれば、仕上焼鈍のままで鋼板地鉄表面が平滑化され、酸洗や電解研磨などの追加工程を必要とせずに鉄損の低減が可能になる。
【図面の簡単な説明】
【図１】実施例３における仕上焼鈍条件の概略を示したヒートパターン図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a grain-oriented electrical steel sheet having a low iron loss, which is mainly used as an iron core of a power transformer, and a method for finish annealing. In particular, by reducing the iron loss by forming an oxide film such as forsterite on the surface in an easily peelable mode and then peeling it off.
[0002]
[Prior art]
Grain-oriented electrical steel sheets containing Si and having a crystal orientation of (110) [001] or (100) [001] are widely used as various iron core materials because of their excellent soft magnetic properties. ing. The characteristic required of the magnetic steel sheet is generally a loss when magnetized to 1.7 T at a frequency of 50 Hz. _17/50 It is important that the iron loss, represented by the value (W / kg), be low and that the coercive force be small as a soft magnetic material.
[0003]
In order to reduce the iron loss, it is effective to reduce the eddy current loss (We) and the hysteresis loss (Wh). First, in order to reduce eddy current loss, there are a method of increasing electric resistance by containing Si, a method of reducing the thickness of a steel sheet, a method of further reducing the crystal grain size, and the like. A method is known in which the <100> axis of crystal grains is highly aligned in the rolling direction.
[0004]
Among them, the method of excessively containing Si has a disadvantage of causing a decrease in saturation magnetic flux density and causing an increase in the size of the iron core, and a method of reducing the thickness of the steel sheet also has a disadvantage of extremely increasing the manufacturing cost. In each case, there was a limit in reducing iron loss.
[0005]
On the other hand, in the method of aligning the crystal orientation, the magnetic flux density B ₈ Thus, it is possible to obtain a product having a value of about 1.96 to 1.97 T, but there is little room for further improvement.
[0006]
Furthermore, a technology has been developed to artificially narrow the magnetic domain width and reduce iron loss by applying a plasma jet or laser beam to locally introduce strain on the steel sheet surface, or by forming grooves on the steel sheet surface. As a result, a significant iron loss reduction effect was obtained. However, there is a limit to the iron loss reduction effect of this technology.
[0007]
Apart from these techniques, Patent Document 1 discloses that the roughness of the interface between the surface of the steel plate and the non-metallic coating is reduced, that is, the surface of the steel plate is smoothed, and the material is further subjected to a tension applying treatment. It is reported that the iron loss of the steel is greatly reduced.
[0008]
[Patent Document 1]
Japanese Patent Publication No. 52-24499
[0009]
Here, usually used at the time of secondary recrystallization annealing of directional silicon steel, MgO-based annealing separator, to form a large amount of dense coating mainly composed of forsterite on the steel sheet surface after annealing, The surface roughness of the steel plate is not reduced, and it is inconvenient for mirror polishing or thermal etching for obtaining a further mirror surface.
[0010]
As a method of suppressing the formation of the forsterite film, for example, Patent Document 2 proposes a method of applying an annealing separator obtained by adding 2 to 40 parts by mass of an alkali or alkaline earth metal chloride to MgO. . However, the technique described therein focuses on suppressing the forsterite film, and there is room for further improvement in the magnetic properties of the obtained steel sheet.
[0011]
[Patent Document 2]
JP-A-64-62476
[0012]
Patent Document 3 proposes a method of suppressing the formation of a forsterite film by using alumina as an annealing separator. However, when alumina is used as the main component of the annealing separator, the purification of the inhibitor contained in the steel to cause secondary recrystallization such as sulfide, selenide, and nitride becomes insufficient. There was a problem. In addition, although not as large as a normal forsterite film, there is a problem that a slight oxide containing Si or Al is formed on the surface layer and it is difficult to obtain a completely smooth surface.
[0013]
[Patent Document 3]
JP-A-5-156362
[0014]
In order to solve these problems, Patent Literature 4 proposes a technique in which the ratio of hydrogen in the atmosphere is changed according to the equilibrium dissociation partial pressure of chloride as an annealing separator. According to this technology, for example, MgC1 ₂ When Al is added, the hydrogen ratio is reduced to 0% and AlC1 ₃ Is added, the hydrogen ratio is reduced to 0 to 25%, and BiCl is added. ₂ When hydrogen is added, the hydrogen ratio is preferably set to 0 to 100%. However, there is still room for further iron loss reduction even in steel sheets to which this technology is applied.
[0015]
[Patent Document 4]
JP-A-5-204393
[0016]
[Problems to be solved by the invention]
Therefore, an object of the present invention is to provide a method for producing a grain-oriented electrical steel sheet and a method for finish annealing, which reduce the iron loss by smoothing the surface of the steel sheet base iron.
[0017]
[Means for Solving the Problems]
The inventors have conducted intensive studies on a technique for smoothing the steel sheet surface using an annealing separator containing a halide such as chloride, and as a result, suppressed the formation of a forsterite film as in the conventional method. Instead, the present inventors have found that the surface smoothness of a steel sheet can be advantageously advanced by appropriately forming a forsterite film in a form that is easy to peel off.
[0018]
Further, the ratio of the magnesium oxide and / or hydroxide in the metal oxide and / or metal hydroxide contained in the annealing separator and the ratio of hydrogen in the temperature range during finish annealing are optimized. As a result, an appropriate forsterite film can be formed, and by adding one or more selected from metal chlorides, metal bromides and metal iodides to the annealing separator, an appropriate amount of forsterite is obtained. The inventors have found that the formation of the film can be promoted and the forsterite film can be easily peeled off, and the present invention has been completed.
[0019]
The gist configuration of the present invention is as follows.
(1) A steel slab containing 2.0 to 7.0 mass% of Si is subjected to annealing and rolling to form a cold-rolled sheet having a final thickness, and then subjected to primary recrystallization annealing to obtain an annealing separator. In the method for producing a grain-oriented electrical steel sheet to be coated and subjected to finish annealing to cause secondary recrystallization,
The annealing separator comprises a metal oxide and / or metal hydroxide in which the total content of magnesium oxide and / or hydroxide is 20% by mass or more, and metal chloride, metal bromide and metal iodide. One or two or more selected from the above, the former 100 parts by mass, chlorine, bromine and iodine in the latter in a total content of 0.1 to 10 parts by mass, resulting in a composition,
The finish annealing is performed in an atmosphere having a low hydrogen ratio of 0 to 25% by volume in a first temperature range in which the temperature is raised to a specific temperature of at least 950 ° C., and a second temperature in which the temperature is raised to a specific temperature or more and the temperature is kept uniform. A method for producing a low iron loss grain-oriented electrical steel sheet, wherein the method is performed in an atmosphere having a high hydrogen ratio of more than 25% by volume in a region.
[0020]
(2) The metal ion of metal chloride, metal bromide and metal iodide is one or two or more metal ions selected from Cu, In, Sn and Sb ions. 1) The method for producing a low iron loss grain-oriented electrical steel sheet according to the above.
[0021]
(3) The metal ion of metal chloride, metal bromide and metal iodide is one or two or more metal ions selected from Zn, Ag, Pb and Bi ions. 1) The method for producing a low iron loss grain-oriented electrical steel sheet according to the above.
[0022]
(4) A method in which a steel sheet containing Si: 2.0 to 7.0 mass% is subjected to finish annealing for producing secondary recrystallization to produce a grain-oriented electrical steel sheet,
In the steel sheet, a metal oxide and / or metal hydroxide in which the total content of magnesium oxide and / or hydroxide is 20% by mass or more, and a metal chloride, a metal bromide and a metal iodide One or two or more kinds selected from the group consisting of the former, 100 parts by mass of the former, and the latter containing chlorine, bromine and iodine in a ratio of 0.1 to 10 parts by mass in total, and an annealing separator is applied. After that, the finish annealing is performed in an atmosphere having a low hydrogen ratio of 0 to 25% by volume in the first temperature region where the temperature is raised to at least the specific temperature of 950 ° C. or more, and the temperature is raised to the specific temperature or more and maintained at a uniform temperature. A finish annealing method for a low iron loss grain-oriented electrical steel sheet, which is performed in an atmosphere having a high hydrogen ratio of more than 25% by volume in a second temperature range.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described specifically. First, with respect to the electromagnetic steel sheet of the present invention, a known method can be applied to a manufacturing method before finish annealing. The desirable configuration will be described.
[0024]
First, as the component composition of the steel sheet used in the present invention, Si is 2.0 to 7.0. It is essential to contain O mass%. That is, Si is an effective component for increasing the electrical resistance of the product and reducing iron loss. If the content exceeds O% by mass, the hardness becomes high, manufacturing and processing become difficult, and the saturation magnetic flux density also decreases. On the other hand, 2. If the amount is less than O mass%, transformation occurs during the secondary recrystallization annealing, and a stable secondary recrystallization structure cannot be obtained. O mass%.
[0025]
Further, by containing Al as an inhibitor component in the initial steel in an amount of 0.01% by mass or more, the crystal orientation can be improved. When Al is added, if the content exceeds 0.06% by mass, the crystal orientation deteriorates again. Therefore, the content is preferably set to 0.06% by mass or less. Nitrogen has a similar effect, and the upper limit is preferably set to 200 ppm by mass for suppressing the occurrence of blister defects, and the lower limit is not particularly defined, but it is economically difficult to industrially reduce the amount to less than 10 ppm by mass. Therefore, the lower limit is preferably set to 10 mass ppm.
[0026]
Here, it is advantageous to add a step of performing a nitrogen enrichment treatment described later after the primary recrystallization annealing from the viewpoint that the restriction on the slab heating temperature is released and the degree of freedom of operation is increased. When the treatment is not performed, it is recommended that the initial steel contains 0.01 to 0.06 mass% of the sum of Se + S. In addition, in order to precipitate these as Mn compounds, it is desirable to contain 0.01 to 0.2% by mass of Mn. If each is too small, the precipitates to cause secondary recrystallization will be too small, and if too large, solid solution before hot rolling tends to be difficult, so they are added within the respective lower and upper limits. Is preferred.
[0027]
On the other hand, when performing the nitrogen increasing treatment, Mn, Se and S are not necessarily required, but may be appropriately added for the purpose of improving the ductility of the steel. In this case, it is preferable that the contents of Mn, Se, and S are also the same as the above-mentioned preferred ranges for the same reason as described above.
[0028]
Further, in the steel, in addition to the above-mentioned elements, B, Bi, Sb, Mo, Te, Sn, P, Ge, As, Nb, Ni, Cr, which are additional components suitable for the production of grain-oriented electrical steel sheets. The elements selected from Ti, Cu, Pb, Zn and In are used alone or in combination of 0.0005 to 2. It is preferable to contain O mass%. When the content is less than 0.0005% by mass, the effect is not remarkably recognized, while 2. If it exceeds O mass%, the magnetic flux density may be reduced. Further, 0.005 to 0.8% by mass of C may be added to the initial steel for the purpose of controlling the recrystallization texture and improving the magnetic properties.
[0029]
Elements such as C, S, Se and N all have harmful effects on magnetic properties, and particularly deteriorate iron loss. Therefore, in a product plate, C: 0.003% by mass or less, S and S respectively. Se: It is preferable to reduce each to 0.002% by mass or less and N: 0.002% by mass or less. In particular, in order to achieve the desired properties of the present invention, it is extremely important that the amount of carbides in steel existing as precipitates be less than 30 ppm by mass.
[0030]
Next, a method for manufacturing a grain-oriented electrical steel sheet according to the present invention will be described in detail. That is, from a steel ingot or slab adjusted to a predetermined component, a final thickness is obtained by hot rolling by a known method, and then by cold or warm rolling. The present invention is also applicable to a material obtained by a continuous hot rolling method, a sheet bar casting method, or a coil casting method. Thereafter, primary recrystallization annealing and, if necessary, nitrogen increasing treatment are performed.
[0031]
Here, the nitrogen increasing treatment is a treatment performed on a daily basis to omit the high-temperature heating treatment for dissolving the inhibitor used as AlN during the hot rolling. Specifically, the steel plate after the primary recrystallization is heated and passed in an atmosphere containing ammonia.
[0032]
Next, an annealing separator mainly composed of an oxide such as magnesia, calcia, alumina, and forsterite is attached to the steel sheet. Magnesia and calcia may be hydrated to form a hydroxide. Here, the proportion of magnesia (magnesium oxide and / or hydroxide) in the metal oxide and / or metal hydroxide contained in the annealing separator is 20 to 100% by mass in total. Needs to be 20 to 100% by mass. This is to supply magnesium necessary for forming an appropriate forsterite film on the steel sheet surface during the finish annealing. In the present invention, a method is used in which forsterite is once formed and the surface is smoothed by exfoliating the forsterite, but if the proportion of magnesia is less than 20%, formation of an appropriate forsterite film required for surface smoothing is performed. Therefore, the lower limit was set to 20% by mass. Since the metal oxide and / or metal hydroxide may be magnesia alone, there is no particular upper limit on the proportion of magnesia.
[0033]
The standard of the amount of the annealed separating agent is about 2 to 50 g / m. ² The slurry may be applied in a water slurry and applied or dried, or may be electrostatically applied.
[0034]
Further, in the present invention, the annealing separator contains an appropriate amount of one or more selected from metal chlorides, metal bromides and metal iodides in addition to the metal oxide and / or metal hydroxide. It is necessary that the composition be as follows. As a result, the forsterite film formed by the reaction between magnesia in the annealing separator and the Si-containing oxide on the surface of the base iron in the finish annealing can be easily peeled, and the surface of the base steel is smooth when the finish annealing is completed. Can be obtained.
[0035]
Here, metal ions of metal chlorides, metal bromides and metal iodides include, for example, alkali metals and alkaline earth metals, as well as Al, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, and Ag. , In, Sn, Sb, Pb, Bi and the like. Among these metal ions, in particular, Cu, In, Sn and Sb ions are partially taken into the base iron during finish annealing, act as an inhibitor, and increase the degree of integration of the crystal orientation in the Goss orientation, This is suitable because it has the effect of improving the magnetic properties. Further, Zn, Ag, Pb and Bi ions have a great effect of improving the smoothness of the surface of the base iron, and are suitable for reducing iron loss. Here, as the metal chloride, bromide, and iodide, in addition to the compound composed of the metal and the halide, for example, a compound containing an element such as oxygen such as SbOCl, or SnC1 ₂ ・ 2H ₂ It may be a compound containing bound water such as O.
[0036]
Chloride, bromide and iodide of these metals have a low melting point, melt from a relatively low temperature in the early stage of temperature rise in finish annealing, wet the surfaces of magnesia and ground iron in the annealing separator, and react with each other. Promotes the formation of a forsterite coating. In this way, the forsterite film formed at a low temperature by the action of chlorides and the like has a flat interface with the ground iron, and the so-called anchor, which is seen in the forsterite film of the conventional oriented silicon steel sheet, develops. do not do. Therefore, in the cooling process of the finish annealing, the steel sheet is easily separated due to a difference in thermal expansion with the steel sheet, and the surface of the ground iron after the separation is smoothed. In addition, since the forsterite coating once formed adheres to the steel sheet surface during the finish annealing, it has an effect of suppressing unnecessary additional oxidation in a high-temperature region and assisting smoothing of the surface by thermal etching. Further, when S or Se is contained as an inhibitor component in steel, it has an action of extracting these elements from the steel to the surface, which is extremely useful.
[0037]
As described above, in the finish annealing, the technical idea of the present invention that the forsterite film is formed in such a form that the forsterite film is easily peeled at the time of heating (heating) or holding the heating temperature, and the forsterite film is peeled at the time of cooling, This is significantly different from the conventional technical idea of smoothing the surface by inhibiting and suppressing.
[0038]
Further, in the present invention, the appropriate range of the content of metal chloride, metal bromide and metal iodide to be contained in the annealing separator is 100 parts by mass of metal oxide and / or metal hydroxide, chlorine, It is necessary that the total amount of bromine and iodine be 0.1 to 10 parts by mass. If the content of the metal chloride, the content of the metal bromide and the content of the metal iodide is less than 0.1 part by mass in the above ratio, the formation promoting effect of the forsterite film which is easy to peel off cannot be obtained, On the other hand, if the amount is more than 10 parts by mass, the forsterite forming reaction becomes excessive, and the forsterite is formed so as to bite into the inside of the base steel, thereby preventing peeling during cooling and deteriorating magnetic properties.
[0039]
In addition, known sulfides, hydroxides, borates, nitrates, phosphates, carbonates and / or sulfates may be further added to the annealing separator to control the secondary recrystallization.
[0040]
Next, the steel sheet to which the annealing separating agent is adhered is subjected to finish annealing in a coiled or laminated state to cause secondary recrystallization. In the present invention, the hydrogen ratio in the atmosphere in the final annealing is controlled. It is important to smooth the ground iron surface.
[0041]
First, in the first temperature range in which the temperature is raised from room temperature to a specific temperature of at least 950 ° C. by finish annealing, it is necessary to set an atmosphere in which the hydrogen ratio (partial pressure ratio) is a low hydrogen ratio of 0 to 25% by volume. There is. If the hydrogen ratio exceeds 25%, the formation of forsterite from a low temperature is inhibited, or the flatness with the interface with the base iron is impaired, so that the smoothness of the base steel surface after finish annealing is deteriorated, This is because a problem that the forsterite film remains on the ground iron occurs. The lower limit of the hydrogen ratio may be 0% and is not particularly limited, but the most preferable low hydrogen ratio is in the range of 0 to 5%. It is preferable that the remainder of the atmosphere other than hydrogen is one or both of nitrogen and argon.
[0042]
On the other hand, in the second temperature range in which the temperature is raised to a specific temperature or higher (for example, 950 ° C. or higher) and the temperature is kept constant by finish annealing, the so-called thermal etching in which the interface between forsterite and ground iron is smoothed is effective. Occurs. Therefore, the effect of this thermal etching is promoted by switching to an atmosphere in which the hydrogen ratio in the atmosphere is higher than the specific temperature and the hydrogen ratio in the atmosphere is higher than 25% by volume, and the effect of improving the magnetic properties after finish annealing is remarkably improved. is there. Although the reason is not clear, it is considered that the stability of oxides other than forsterite remaining on the surface of the steel sheet is lowered, or a metal element generated by decomposition of a halide acts on the surface of the ground iron.
[0043]
Further, when S or Se is used as an inhibitor component, there is also an effect that these components are excluded from steel, that is, so-called purification is promoted. When the hydrogen ratio is 25% or less, problems such as insufficient surface smoothness and poor purification of S and Se occur. The upper limit of the high hydrogen ratio is not particularly limited and may be 100% by volume, and preferably the high hydrogen ratio is 70 to 100%.
[0044]
By heating (raising the temperature) to a specific temperature or higher (for example, 950 ° C. or higher), preferably 1100 to 1250 ° C. and keeping the temperature uniform in an atmosphere in which the hydrogen ratio is increased, the surface smoothness is improved.
[0045]
In cooling the steel sheet, it is preferable to suppress the oxidation (temper color) of the steel sheet surface by using a non-oxidizing atmosphere until the temperature of the steel sheet is lowered to 200 ° C. or lower.
[0046]
If necessary, the steel sheet after the secondary recrystallization may be further subjected to a smoothing treatment by electrolytic polishing, chemical polishing, physical polishing, thermal etching or the like. Alternatively, a process of electrolyzing in a water-soluble halogen compound (crystal orientation enhancement process), that is, a process utilizing the fact that the electrolysis speed varies depending on the plane orientation of the crystal plate is also advantageously applicable.
[0047]
It should be noted that the present invention can be used in combination with a conventional magnetic domain segmentation technique, and a combined effect of at least additive can be obtained. The domain refining technology here means, for example, a method of irradiating a steel sheet surface of a product with a laser or a plasma jet to locally form a strain region, a method of forming a groove on the steel sheet surface, and coating the structure or composition of the steel sheet surface. And a method of locally changing the same, and a conventionally known method such as a projection roll or an etching method can be applied to the method of manufacturing. Among them, the method of forming a point-like or linear groove region by electrolytic etching in the steel sheet after the secondary recrystallization, without giving a strain to the steel sheet, because it is possible to efficiently provide a groove of an effective cross-sectional shape, Recommended.
[0048]
Further, by providing a tension coating on the steel sheet, iron loss can be effectively improved with a slight tension. Grain-oriented electrical steel sheets are usually used in a laminated state, and in that case, it is required that there is no continuity between layers. Therefore, the above-mentioned tensile coating can have a function as an insulating material, and can be separately provided with an insulating coating. May be provided.
[0049]
Although the thickness of the steel sheet is not particularly specified, the classical eddy current loss among the eddy current losses is a function of the thickness of the steel sheet. Good, usually in the range of 0.1-0.35 mm.
[0050]
【Example】
Example 1
C: 0.05% by mass, Si: 3.2% by mass, Mn: 0.06% by mass, S: 0.02% by mass, Se: 0.001% by mass, Al: 0.02% by mass, N: 1. A steel slab containing 80 ppm by mass, 0.3% by mass of Sn and 0.2% by mass of Cu, and the balance being Fe and unavoidable impurities was heated to 1250 ° C., and then subjected to hot rolling. A hot-rolled sheet of Omm was formed, and a steel sheet having a thickness of 0.21 mm was formed by warm rolling, and then subjected to primary recrystallization annealing also serving as decarburization. Then, the steel sheet was mixed with an annealing separator obtained by mixing alumina and magnesia at various ratios, and further with MgC1. ₂ ・ 6H ₂ O was added at a ratio of 1 part by mass of chlorine (Cl) to 100 parts by mass of alumina and magnesia in total, and was electrostatically applied to the surface of the steel plate. At this time, the adhesion amount of the annealing separator (both sides, the same applies hereinafter) is 14 g / m. ² Met.
[0051]
Next, each of the steel sheets coated with the annealing separator is wound into a coil having an outer diameter of 1.5 m, and then heated up to 800 ° C. in a nitrogen atmosphere at an average of 50 ° C./h. In a nitrogen atmosphere, the temperature was raised at an average of 4.5 ° C./h, and then increased to 1200 ° C. in a hydrogen atmosphere at an average of 14 ° C./h, followed by purification annealing at 1200 ° C. for 6 hours. After the next recrystallization annealing, it was left to cool to obtain a directional magnetic steel strip.
[0052]
The surface of the steel strip thus obtained is washed by washing with water and phosphoric acid and then flattened by holding at 820 ° C. for 20 seconds while applying a tension of 6 MPa in a nitrogen atmosphere containing 3% by volume of hydrogen. This was performed by continuous annealing.
A sample for magnetic measurement was taken from the steel strip thus obtained, subjected to strain relief annealing, and the hysteresis loss at 1.7 T, 50 Hz was determined by DC magnetization measurement using an Epstein frame. Table 1 shows the measurement results of the oxygen basis weight (the same applies to both surfaces, hereinafter) and the hysteresis loss. A smooth ground iron surface was obtained at a magnesia abundance ratio of 20% or more, and the hysteresis loss was reduced. I have.
[0053]
[Table 1]

[0054]
Example 2
C: 0.06% by mass, Si: 3.2% by mass, Mn: 0.06% by mass, Al: 0.02% by mass, N: 80% by mass, Sb: 0.1% by mass. 1. A steel slab composed of Fe and unavoidable impurities is heated to 1400 ° C. by induction heating, and then subjected to hot rolling. An Omm hot-rolled sheet was subjected to hot-rolled sheet annealing, and then cold-rolled with intermediate annealing to obtain a steel sheet having a sheet thickness of 0.21 mm. Thereafter, primary recrystallization annealing also serving as decarburization annealing was performed.
Then, magnesia obtained by adding chlorides, bromides or iodides of various metals to the steel sheet was applied as a water slurry to the steel sheet surface, and baked and dried at 220 ° C. in the atmosphere. At this time, the adhesion amount of the annealing separating agent was 9.5 g / m. ² Met.
[0055]
Next, the coil is heated to 800 ° C. ₂ The temperature is raised at an average of 50 ° C. per hour in an atmosphere, and the temperature is increased from 800 ° C. to 900 ° C. in an argon atmosphere at an average of 4.5 ° C./h, and from 900 ° C. to 1150 ° C. in an argon atmosphere at an average of 20 ° C./h. After raising the temperature, and then performing a secondary recrystallization annealing at 1150 ° C. for 6 hours in a hydrogen atmosphere, a directional magnetic steel strip was obtained.
[0056]
The surface of the steel strip thus obtained is washed by washing with water and phosphoric acid, and further subjected to flattening annealing at 80 ° C. for 30 seconds while applying a tension of 9 MPa, and continuous annealing in a nitrogen atmosphere containing 2% hydrogen. Made by.
A sample for magnetic measurement was taken from the steel strip thus obtained and subjected to strain relief annealing, and then a hysteresis loss at 1.7 T and 50 Hz and a magnetic flux density B at 800 A / m. ₈ And were determined by DC magnetization measurement using an Epstein frame.
[0057]
Table 2 shows the surface morphology and hysteresis loss of the grain-oriented electrical steel sheet thus obtained. In any of the invention examples in which the halide in the range of the present invention is added to the annealing separator, a smoothed ground iron surface and good magnetic properties are obtained. In particular, examples of the invention in which a halide of Cu, In, Sn or Sb is added include B ₈ In particular, the invention examples in which a halide of Zn, Ag, Pb or Bi is added have a small oxygen basis weight and a small hysteresis, and are particularly suitable.
[0058]
[Table 2]

[0059]
Example 3
C: 0.065% by mass, Si: 3.4% by mass, Mn: 0.1% by mass, Al: 0.01% by mass, N: 70% by mass, Se: 0.014% by mass and Sb: O. After heating a steel slab containing Fe and inevitable impurities to 1400 ° C. by induction heating, hot rolling was performed to obtain a 2.0 mm hot-rolled sheet, and hot-rolled sheet annealing was performed. The steel sheet having a thickness of 0.22 mm was formed by warm rolling with intermediate annealing from the above. Thereafter, primary recrystallization annealing also serving as decarburization annealing was performed.
Then, SnC1 was added to this steel sheet with respect to 100 parts by mass of magnesia. ₂ Was added as a water slurry to the surface of the steel sheet, and was baked and dried at 200 ° C. in the air. At this time, the adhesion amount of the annealing separator was 15 g / m. ² Met.
[0060]
Next, the temperature of the coil was increased to 700 ° C. at an average of 50 ° C./hour in a nitrogen atmosphere, and was increased from 700 ° C. to 810 ° C. in an atmosphere A having a low hydrogen ratio at an average of 40 ° C./hour. After the temperature was raised at 8 ° C./h, the temperature was increased from 900 ° C. to 1150 ° C. at an average temperature of 12 ° C./h, and the steel was subjected to secondary recrystallization annealing in which the temperature was maintained for 6 hours. . Here, the atmosphere B was switched to the atmosphere B having a high hydrogen ratio at a specific temperature X of 800 ° C. or higher. The atmospheres A and B were atmospheres of hydrogen or nitrogen alone or in a mixture, and the specific temperature X at which the hydrogen ratio was switched was variously changed. FIG. 1 shows an outline of the annealing temperature and atmosphere.
[0061]
The surface of the steel strip thus obtained is washed by water washing and phosphoric acid washing, and is further subjected to flattening annealing at 810 ° C. for 30 seconds while applying a tension of 9 MPa by continuous annealing in a nitrogen atmosphere containing 2% of hydrogen. I did it.
A sample for magnetic measurement was taken from the steel strip thus obtained, subjected to strain relief annealing, and the hysteresis loss at 1.7 T, 50 Hz was determined by DC magnetization measurement using an Epstein frame.
Table 3 shows the surface morphology and hysteresis loss of the grain-oriented electrical steel sheet thus obtained. When the specific temperature is set to 950 ° C. or more (specifically, in the range of 950 to 1100 ° C. in Table 3) with the hydrogen ratio in the atmosphere of the present invention, the reduction of the oxygen basis weight and the low hysteresis loss on the surface of the base iron are reduced. can get.
[0062]
[Table 3]

[0063]
【The invention's effect】
According to the present invention, the surface of the steel plate base iron is smoothed while the finish annealing is performed, and iron loss can be reduced without requiring an additional step such as pickling or electrolytic polishing.
[Brief description of the drawings]
FIG. 1 is a heat pattern diagram schematically illustrating finish annealing conditions in Example 3.

Claims

After subjecting a steel slab containing Si: 2.0 to 7.0 mass% to annealing and rolling to obtain a cold-rolled sheet having a final thickness, the steel slab is subjected to primary recrystallization annealing, and an annealing separator is applied. In a method for producing a grain-oriented electrical steel sheet to be subjected to finish annealing for causing secondary recrystallization,
The annealing separator comprises a metal oxide and / or metal hydroxide in which the total content of magnesium oxide and / or hydroxide is 20% by mass or more, and metal chloride, metal bromide and metal iodide. One or two or more selected from the above, the former 100 parts by mass, chlorine, bromine and iodine in the latter in a total content of 0.1 to 10 parts by mass, resulting in a composition,
The finish annealing is performed in an atmosphere having a low hydrogen ratio of 0 to 25% by volume in a first temperature range in which the temperature is raised to a specific temperature of at least 950 ° C., and a second temperature in which the temperature is raised to a specific temperature or more and the temperature is kept uniform. A method for producing a low iron loss grain-oriented electrical steel sheet, wherein the method is performed in an atmosphere having a high hydrogen ratio of more than 25% by volume in a region.

2. The metal ion of metal chloride, metal bromide and metal iodide is one or more metal ions selected from Cu, In, Sn and Sb ions. Manufacturing method of low iron loss oriented magnetic steel sheet.

2. The metal ion of metal chloride, metal bromide and metal iodide is one or more metal ions selected from Zn, Ag, Pb and Bi ions. Manufacturing method of low iron loss oriented magnetic steel sheet.

In a method in which a steel sheet containing Si: 2.0 to 7.0 mass% is subjected to finish annealing for producing secondary recrystallization to produce a grain-oriented electrical steel sheet,
In the steel sheet, a metal oxide and / or metal hydroxide in which the total content of magnesium oxide and / or hydroxide is 20% by mass or more, and a metal chloride, a metal bromide and a metal iodide One or two or more kinds selected from the group consisting of the former, 100 parts by mass of the former, and the latter containing chlorine, bromine and iodine in a ratio of 0.1 to 10 parts by mass in total, and an annealing separator is applied. After that, the finish annealing is performed in an atmosphere having a low hydrogen ratio of 0 to 25% by volume in the first temperature region where the temperature is raised to at least the specific temperature of 950 ° C. or more, and the temperature is raised to the specific temperature or more and maintained at a uniform temperature. A finish annealing method for a low iron loss grain-oriented electrical steel sheet, which is performed in an atmosphere having a high hydrogen ratio of more than 25% by volume in a second temperature range.