JP3993689B2 - Strain relief annealing method for laminated core - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、いわゆるセミプロセス無方向性電磁鋼板をコア形成して焼鈍を施す際の焼鈍方法に関し、特に低磁場における鉄損の優れたコアを製造する方法に関する。
【０００２】
【従来の技術】
比較的小型の回転機等のコアは、主に無方向性電磁鋼板を所定の形状に打ち抜いて積層し、溶接、かしめ、接着などの方法により固定して形成される。一般に打ち抜きによる歪みで鉄損が増加し、回転機等のエネルギー効率が低下するので、歪みを除去するためコア形成後に焼鈍する場合がある。焼鈍条件としては、始めに３００〜４００℃で打ち抜き油を除去した後、主にＮ2 やＣＯ2 ，ＣＯなどからなる非酸化性ないし還元性の雰囲気中で、７５０℃に２時間程度保持されるのが通常である。
【０００３】
歪み取り焼鈍について開示された技術の例として、特開昭５４−１８０３号公報では、低融点の熱融着性ガラス系無機物を絶縁被膜として塗布した帯状電磁鋼板から、鉄心コアを打ち抜いて積層した後、７５０℃で２時間焼鈍して、コア形成と歪み取り焼鈍を同時に行なう技術が開発されている。
また、特開昭５９−１２３７１９号公報には、鉄心を誘導加熱による焼鈍するに際して、コアの温度が７２０℃以上の温度Ｔにある時間Ｔｍが、Ｔｍ（分）＝−０．３７×Ｔ（℃）＋３２０、を超えないようにすることで、焼鈍による高磁場での磁束密度低下を防止する技術が開示されている。
【０００４】
コアの材料に用いられる無方向性電磁鋼板は、一般に、鉄にＳｉ，Ａｌなど固有抵抗を増加させる元素を添加し、所定の板厚まで冷延した後焼鈍し、表層に絶縁被膜を形成したものである。添加元素は一般に多いほど鉄損は低くなるが、その分コスト高となり、また飽和磁束密度の低下や加工性の劣化をもたらすので、そのグレードに応じて添加される。現在工業的に生産されている無方向性電磁鋼板のうち最高級グレードのものとしては、例えば、特開昭５９−１００２１８号公報に示されているように、Ｓｉ：２．５〜３．５％、Ａｌ：０．５〜１．０％未満を含有するものが開示されている。
【０００５】
また、この公報ではその製造方法として、冷間圧延後の仕上焼鈍として１０５０℃で３秒以上６０秒未満の間連続焼鈍を行い、再結晶後の平均結晶粒径を１００μｍ以上にすることで良好な磁気特性を得ている。このように、無方向性電磁鋼板としては、最終的な結晶粒径をより大きくすることで、磁気特性、特に低周波数帯域で磁化したときの鉄損を小さくすることができる。そして、これを効果的に行う方法として、コア焼鈍を行うセミプロセス無方向性電磁鋼板に、仕上焼鈍後にスキンパス圧延を行うことで鋼板に歪みを導入し、コア焼鈍における再結晶を促進するという技術も開示されている。
【０００６】
無方向性電磁鋼板の高効率化については、以上のような技術の他にも様々な改善技術が提案され、市場の省エネルギー化への要請に対応してきた。
【０００７】
【発明が解決しようとする課題】
既に述べたように、コアの鉄損増加を抑制するためには、加工歪を除去するためのコア焼鈍が必要である。これはセミプロセス材ばかりではなく、コア焼鈍を要しないとされているフルプロセス材においても考慮すべきものとなっている。
そこで、本発明者らは、このコア焼鈍について種々検討した結果、これまでより更に良好な磁気特性を得られる方法を知見したものである。
【０００８】
【課題を解決するための手段】
（１）無方向性電磁鋼板を積層して形成したコアの焼鈍を、８００℃以上の温度で行い、前記焼鈍における焼鈍雰囲気を非酸化性もしくは還元性雰囲気として、雰囲気中の酸素もしくは水分濃度を１％未満、もしくはＰＨ 2 Ｏ／ＰＨ 2 を０．１以下とすることを特徴とする積層コアの歪み取り焼鈍方法。
（２）前記焼鈍雰囲気に水素を添加して、雰囲気中のＰＨ2 Ｏ／ＰＨ2 を調整することを特徴とする（１）記載の積層コアの歪み取り焼鈍方法。
（３）前記積層して形成したコアの焼鈍を８５０℃以上の温度で行うことを特徴とする（１）〜（２）のいずれか１項に記載の積層コアの歪み取り焼鈍方法。
（４）前記無方向性電磁鋼板のＡｌ含有量が０．１重量％未満であることを特徴とする（１）〜（３）のいずれか１項に記載の積層コアの歪み取り焼鈍方法。
（５）前記無方向性電磁鋼板のＡｌ含有量が０．１重量％以上であり、かつ積層して形成したコアの焼鈍の雰囲気における窒化能を有するガスの濃度を容量比で３０％未満とすることを特徴とする（１）〜（３）のいずれか１項に記載の積層コアの歪み取り焼鈍方法。
（６）前記焼鈍雰囲気にＨｅ，Ａｒなどの不活性ガスを添加して、雰囲気の酸化度および／または窒化ガス濃度を調整することを特徴とする（１）〜（５）のいずれか１項に記載の積層コアの歪み取り焼鈍方法。
（７）前記焼鈍における非酸化性もしくは還元性雰囲気が、不活性ガスおよび／または水素、および不可避的混入ガスよりなることを特徴とする（１）〜（６）のいずれか１項に記載の積層コアの歪み取り焼鈍方法。
（８）前記積層コア形成に用いる無方向性電磁鋼板として、結晶粒径が５０μｍ以下の鋼板を用いることを特徴とする（１）〜（７）のいずれか１項に記載の積層コアの歪み取り焼鈍方法。
（９）前記積層コア形成に用いる無方向性電磁鋼板として、最終冷延後に仕上げ焼鈍を施さない鋼板を用いることを特徴とする（１）〜（７）のいずれか１項に記載の積層コアの歪み取り焼鈍方法。
【０００９】
【発明の実施の形態】
以下に本発明について詳細に説明する。
本発明の特徴は、コアに形成した後で行う焼鈍を、従来通常に行われている約７５０℃より更に高い８００℃以上、望ましくは８５０℃以上の温度で行うことにある。このような条件による最大の効果は、高温焼鈍により再結晶および加工歪み開放がより促進されることで、特に低磁場における鉄損を更に向上できることにある。この傾向はより高級品、すなわち添加元素を増加させたことで再結晶抑制効果が増大し、かつ加工歪みの復元に大きなエネルギーを要する材料に対して特に効果がある。
【００１０】
また従来、コア焼鈍を前提とした無方向性電磁鋼板に対し、仕上げ焼鈍後にスキンパス圧延を行うことによって、その後の歪み取り焼鈍における再結晶を促進させる技術が知られているが、本発明による積層コアの歪み取り焼鈍方法を用いれば、このようなスキンパス圧延を省略しても、十分な鉄損特性を得ることが可能となる。更に、スキンパス圧延と本発明による歪み取り焼鈍方法を組み合せて、再結晶促進効果を更に高めることも可能である。
【００１１】
以上のような効果を得るためには、８００℃以上、望ましくは８５０℃以上の温度で行うことが必要である。例えば、従来法の約７５０℃という低い温度でも、再結晶は十分な焼鈍時間をかければ進行するが、必要な時間は温度を低くするにつれ指数的に増加するので、工業的には好ましくない。
また、更に、本発明による高温でのコア焼鈍を施すことで、連続焼鈍での結晶粒成長にかかわらず、その成分系における最適な鉄損を得ることができる。更には、最終仕上焼鈍を行わない材料を用いてコアを形成させる場合においても、鉄損を大きく改善することができる。このように、連続焼鈍過程での焼鈍の度合いを自由に選定できることで、連続焼鈍を高温で行うための設備の配慮を省略し、かつ操業コストを低下させるとともに、コア形成のための打ち抜き加工の生産性向上を指向できる。通常、無方向性電磁鋼板の打ち抜き加工においては、焼鈍による粒成長を十分に行った方が鋼板は柔らかくなり、打ち抜き型の長寿命化には効果的である一方、粒成長を完全に行わなければ鋼板は固く、延びにくくなり、打ち抜き時の寸法精度や自動かしめ性を得る上ではむしろ好ましい。従来は必要とする磁気特性に応じて成分系が決定され、それにより鋼板の加工性も自ずと規定されていたが、本発明による積層コアの歪み取り焼鈍法を用いる場合、むしろ打ち抜き加工性を適切な材質となるような温度での連続焼鈍を行い、コア加工後の焼鈍でそれを補うように再結晶を行うことが可能となる。
【００１２】
焼鈍温度の上限については特に規定しない。一般に高温にすればそれだけ磁気特性が向上しやすく、また焼鈍時間も短縮できるが、時間当たりの燃料コストは高くなる。また、高温にするほど絶縁被膜の破壊や窒化が進行しやすいので、制限する必要がある。より好適な条件は８８０〜９７０℃の間である。
また、焼鈍時間についても特に規定しない。極く短時間でも本願発明の温度まで加熱すれば、再結晶および加工歪みの開放は進行し、鉄損は改善される。ただし、この温度はコアのすべての部位で到達する必要があり、従って焼鈍設備の特性やコアの大きさ等に応じて十分な時間を取る必要がある。一方、上限は鉄損向上の観点からは特に規定されるものではないが、長時間操業すればそれだけコスト高となるのに対し、鉄損改善の効果は長くても数時間で飽和する。また、絶縁被膜の劣化も懸念されるため制限される。通常は均熱温度の保持時間を２〜１０時間とし、加熱、冷却時間を合わせておよそ２０時間程度焼鈍される。
【００１３】
また、γ相に変態する材料をＡ1 変態点以上に加熱して一旦変態させると、炭化物、硫化物など粒成長を阻害する物質を再固溶・析出凝集させることができ、再結晶促進の上で効果がある。ただし、この場合はα相に戻ってからの再結晶時間を一定以上確保する必要があるため、冷却速度として、Ａｒ3 変態点から６５０℃までの冷却速度を一定以下とする必要がある。この速度は平均で５０℃／sec 以下が必要である。γ変態を起こす材料の条件は、おおよそＳｉ≦２．５重量％、Ａｌ≦１．０重量％、かつ（Ｓｉ＋２Ａｌ）≦２．５重量％の成分として含むことが好ましい。
【００１４】
本発明のような比較的高い温度でのコア焼鈍が従来行われていなかった理由は２つ考えられる。一つは絶縁被膜の破壊や鋼板表面の酸化の恐れがあること、もう一つは一定以上Ａｌを含有する材料に対して窒化によりＡｌＮが生成し、再結晶を阻害することである。
絶縁被膜の焼損や鋼板表面の酸化を防止するためには、コア焼鈍の雰囲気として非酸化性もしくは還元性雰囲気で行う必要がある。酸化性雰囲気、すなわち酸素、水分、もしくは熱分解でこれらを放出する気体を一定以上含有していると、絶縁被膜の破壊を促進し、また鋼板表層で酸化物が形成されて地鉄に対しピンニングによる鉄損劣化を起こす。
【００１５】
使用される雰囲気ガスとしては、Ｎ2 ，ＣＯ，ＣＯ2 を主成分とする燃焼ガスが多く用いられている。すなわち、燃料を燃焼させてコアを加熱し、またその熱で乾燥させた排ガスを加熱して炉内に吹込むのである。燃焼排ガスの水分含有量は、露点にしておよそ５５℃（約１６ vol％）になる。このガスを冷却して乾燥させることで露点にして１５℃（約１．７ vol％）位としている。従来技術の比較的低い温度でのコア焼鈍で、かつクロム酸などを主成分とする無機被膜では、上記の水分含有量にすれば特に問題とならないが、本発明のように高温で焼鈍する場合、酸化反応は進行しやすく、品質に及ぼす影響は非常に大きい。これを避けるためには、Ｎ2 ，Ｈ2 ，Ａｒなどの単離ガス、アンモニアの分解ガス（Ｈ2 ：Ｎ2 ＝３：１）など、酸化性の非常に低いガスを混合して、実質的な酸素ポテンシャル（ＰＨ2 Ｏ／ＰＨ2 ）を低下させてやるとよい。例えば、露点１５℃のガスなら、水素を１７％以上混入させ、ＰＨ2 Ｏ／ＰＨ2 を０．１以下にすることで、リン酸塩などからなる無機被膜なら劣化は殆んど見られなくなる。ただし、樹脂などの有機物を含有する被膜の場合、更に酸素ポテンシャルを下げて酸化を防止する必要がある。このような場合は、焼鈍するコアをカバーして雰囲気を外気から遮断し、純度の高い特定のガスを用いる。この場合も不活性ガスや水素を適宜混入させ、もしくはこれらのガスを主成分として用いることで、酸素ポテンシャルを更に低下させ、被膜の劣化をより効果的に抑制することができる。
【００１６】
また、窒化によるＡｌＮ生成に対しては、雰囲気ガス中から窒化能を持つガスを減少させる必要がある。本発明の主旨がコアでの再結晶促進にあることから、再結晶を阻害する要因はできるだけ排除しなくてはならない。通常、Ａｌは磁気特性向上のため添加され、その量は高級グレードで約１％である。一方、Ｎは製鋼段階で通常０．０１％以下に抑え、ＡｌＮ生成を抑制している。しかしながら、Ａｌを０．１％以上含む材料においては、その後の熱処理において雰囲気ガス中の窒素を吸収してＡｌＮを形成する。特に、コア焼鈍は焼鈍時間が連続焼鈍と比べ長いため窒化量が多くなりやすく、本発明のように高い温度で焼鈍する場合には更に窒化しやすい。
【００１７】
以上のことから、本発明の焼鈍雰囲気として、鋼板がＡｌを０．１重量％以上含有する場合には、窒化能を有するガスの割合を体積比で３０％未満と規定した。これは対象のガスを窒素としたときの場合の限定値であるが、アンモニアやＮＯx のように、鋼板に対する窒化能の高いガスについては特に、その含有量を０．１％未満とする必要がある。なお、Ａｌの含有量が０．１％未満の場合は、鋼板の窒化は殆んど起こらず、生成されるＡｌＮの量は本発明の効果を阻害するに至らないので、上記のような制限は特に必要ない。
【００１８】
本発明に用いる無方向性電磁鋼板の組成や製造方法は特に限定しない。一般に無方向性電磁鋼板のグレードは、添加元素の量や仕上焼鈍温度、熱延、冷延などの工程条件により決まる鉄損と飽和磁束密度によって定められており、磁気特性と価格との見合いで適切な材料が選択されている。本発明による積層コアの歪み取り焼鈍方法は、ほぼあらゆるグレードに対して、従来法以上の鉄損改善効果をもたらすものである。
【００１９】
本発明で用いる無方向性電磁鋼板に添加される鋼中成分としては、以下のものがある。
Ｓｉは固有抵抗を増加させ、鉄損を低下させる重要な元素であるが、多すぎると加工性が劣化する。通常は５％以下添加される。
Ａｌもまた固有抵抗を増加させ、鉄損を低下させる重要な元素であるが、多すぎると加工性が劣化する。通常は２％以下添加される。
【００２０】
Ｃは一定以上存在すると、電気機器のコアとして使用中に磁気時効を起こして磁気特性を劣化させるので０．０１％以下に制限する必要がある。このような含有量には溶鋼段階で調整する他、連続仕上焼鈍で弱酸化性雰囲気により脱炭する方法も用いられる。
Ｎは多いとＡｌと結合してＡｌＮを形成し、粒成長を阻害するので、溶鋼段階で０．０１％以下に制限する必要がある。
【００２１】
Ｓは溶鋼段階で不可避的に混入するが、多いとＭｎなどと結合して粒界に析出し、再結晶を阻害するので、０．０１％以下に制限する必要がある。
その他、磁気特性、加工性、耐銹性の向上を目的として、Ｍｎ，Ｐ，Ｂ，Ｎｉ，Ｃｒ，Ｓｂ，Ｓｎ，Ｃｕなどを含有させる。その添加量は狙いとする鋼板の特性に応じて決定される。
【００２２】
以上の成分からなる連続鋳造スラブもしくは鋼塊を、熱延し、１回または中間焼鈍をはさむ２回以上の冷延を施し、仕上焼鈍を施し、絶縁被膜を焼付塗布して、無方向性電磁鋼板に仕上げる。この工程において、連続鋳造で熱延板相当の薄スラブとして熱延を省略することも可能である。また、磁気特性を向上させる目的で、熱延板を焼鈍する、もしくは熱延後に巻取り温度を高くして自己焼鈍を行う場合もある。
【００２３】
以上のような成分系、製造方法を適正に選択することで、鋼板の鉄損を非常に小さくすることができる。そして本発明による歪み取り焼鈍方法はこの鉄損を更に減少させるものである。また、より安価な鋼板を用いて良好な鉄損特性を得ることもできる。すなわち、仕上焼鈍温度を低くしたり、もしくは省略したりすることでコストダウンを図った材料に対しても、コアを形成した後に本発明による歪み取り焼鈍を施すことで、従来方法によるよりも低い鉄損特性を得ることが可能となるのである。
【００２４】
【実施例】
＜実施例１＞
表１に示す成分、製造方法で製造された板厚０．５mmの無方向性電磁鋼板を用いてコアを形成し、このコアを燃焼ガス、窒素＋水素、水素のみの３種類の雰囲気中で、均熱温度を７５０〜９５０℃、均熱時間を２時間で焼鈍を施した。鉄損（Ｗ15/50 ）の結果を表２に、絶縁被膜の状況を表３に示す。
【００２５】
Ａｌの含有量が０．１％未満の材料Ｃ，Ｄでは、雰囲気組成に関わらず焼鈍温度が高いほど鉄損は改善されたのに対し、Ａｌを０．３％含有する材料Ａ，Ｂでは、窒素を含有する雰囲気では９００℃以上で鉄損が劣化した。
また絶縁被膜の状況は、雰囲気ガスに水素のみを用いた場合、すべての素材で９５０℃までほとんど劣化は見られず、また水素＋窒素混合ガスでも９００℃まで劣化は見られなかった。一方燃焼ガスでは、８５０℃以上で被膜の劣化が顕著となった。
【００２６】
【表１】
【表２】
【表３】
＜実施例２＞
表１のＢの無方向性電磁鋼板を所定の形状に打ち抜いて積層し、コアを形成した。このコアを表４に示す雰囲気条件で、均熱９００℃×２時間で焼鈍を行なった。鉄損（Ｗ15/50 ）および絶縁被膜の状況を表４に示す。
磁気特性は、雰囲気に一定以上の窒素またはアンモニアを含む No.１，２，３，４，６の条件では焼鈍により殆んど向上しなかった。
【００３０】
また被膜状況は、雰囲気中水素の多い No.５，６で特に劣化が少ないものが得られた。
【００３１】
【表４】
＜実施例３＞
表５に示す成分系、製造方法で製造された無方向性電磁鋼板を所定の形状に打ち抜いて積層し、コアを形成した。このコアを水素９９％の雰囲気で、均熱９００℃×２時間焼鈍した。焼鈍前後の結晶粒径および鉄損（Ｗ15/50）を表６に示す。
【００３３】
コア焼鈍前の結晶粒径が５０μｍ以下の素材を用いた場合でも、本発明のコア焼鈍方法を用いることで、磁気特性の良好な１００〜１５０μｍにすることができる。特に素材ｅでは、仕上焼鈍を行なわないものでも行なったものとほぼ同等の磁気特性を得ることができた。
【００３４】
【表５】
【表６】
【発明の効果】
以上説明したように、本発明による積層コアの歪み取り焼鈍方法を用いることで、連続焼鈍工程やその後のスキンパスを簡略化もしくは省略しても、モーター等のコアの磁気特性を著しく向上させ、かつコアを加工する際の加工性を向上させることが可能となる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an annealing method for forming a core of a so-called semi-processed non-oriented electrical steel sheet, and more particularly to a method of manufacturing a core having excellent iron loss in a low magnetic field.
[0002]
[Prior art]
The core of a relatively small rotating machine or the like is mainly formed by punching a non-oriented electrical steel sheet into a predetermined shape and stacking them, and fixing them by a method such as welding, caulking, or bonding. In general, the iron loss increases due to the distortion caused by punching, and the energy efficiency of a rotating machine or the like decreases. Therefore, annealing may be performed after the core is formed in order to remove the distortion. As annealing conditions, the punching oil is first removed at 300 to 400 ° C., and then kept at 750 ° C. for about 2 hours in a non-oxidizing or reducing atmosphere mainly composed of N 2 , CO 2 , CO, and the like. It is normal.
[0003]
As an example of the technique disclosed for strain relief annealing, Japanese Patent Laid-Open No. 54-1803 discloses a technique in which an iron core is punched and laminated from a strip-shaped electrical steel sheet coated with a low melting point heat-fusible glass-based inorganic material as an insulating film. Thereafter, a technique has been developed in which annealing is performed at 750 ° C. for 2 hours to simultaneously perform core formation and strain relief annealing.
Japanese Patent Application Laid-Open No. 59-123719 discloses that when an iron core is annealed by induction heating, the time Tm at which the core temperature is at a temperature T of 720 ° C. or higher is Tm (min) = − 0.37 × T ( C)) +320, a technique for preventing a decrease in magnetic flux density in a high magnetic field due to annealing is disclosed.
[0004]
The non-oriented electrical steel sheet used for the core material is generally formed by adding an element that increases the specific resistance such as Si or Al to iron, cold-rolling to a predetermined thickness, and annealing to form an insulating coating on the surface layer. Is. In general, the more additive elements, the lower the iron loss. However, the cost is increased, and the saturation magnetic flux density is lowered and the workability is deteriorated. Therefore, it is added according to the grade. Among the non-oriented electrical steel sheets currently industrially produced, as the highest grade, for example, as shown in JP-A No. 59-1000021, Si: 2.5-3.5 %, Al: those containing 0.5 to less than 1.0% are disclosed.
[0005]
Further, in this publication, as a manufacturing method thereof, it is preferable that continuous annealing is performed at 1050 ° C. for 3 seconds or more and less than 60 seconds as a finish annealing after cold rolling, and the average crystal grain size after recrystallization is set to 100 μm or more. Magnetic properties are obtained. As described above, as the non-oriented electrical steel sheet, by increasing the final crystal grain size, it is possible to reduce the magnetic characteristics, particularly the iron loss when magnetized in the low frequency band. And as a method of effectively doing this, a technology that introduces strain to the steel sheet by performing skin pass rolling after finish annealing on semi-processed non-oriented electrical steel sheet that performs core annealing, and promotes recrystallization in core annealing. Is also disclosed.
[0006]
In order to improve the efficiency of non-oriented electrical steel sheets, various improvement techniques have been proposed in addition to the above-described techniques, and the demand for energy saving in the market has been met.
[0007]
[Problems to be solved by the invention]
As described above, in order to suppress an increase in core loss of the core, core annealing for removing processing strain is necessary. This is to be considered not only for semi-process materials but also for full-process materials that do not require core annealing.
Thus, as a result of various studies on the core annealing, the present inventors have found out a method for obtaining even better magnetic characteristics than before.
[0008]
[Means for Solving the Problems]
(1) the annealing of the core formed by laminating the non-oriented electrical steel sheet, are performed by the temperature above 800 ° C., an annealing atmosphere in the annealing as a non-oxidizing or reducing atmosphere, oxygen or moisture concentration in the atmosphere Is less than 1%, or PH 2 O / PH 2 is 0.1 or less .
( 2 ) The method for removing distortion of a laminated core according to ( 1 ), wherein hydrogen is added to the annealing atmosphere to adjust PH 2 O / PH 2 in the atmosphere.
( 3 ) The method of removing annealing of a laminated core according to any one of (1) to ( 2 ), wherein the laminated core is annealed at a temperature of 850 ° C. or higher.
( 4 ) Al content of the non-oriented electrical steel sheet is less than 0.1% by weight, (1) to ( 3 ), wherein the laminated core is subjected to strain relief annealing.
( 5 ) The non-oriented electrical steel sheet has an Al content of 0.1% by weight or more, and the concentration of the gas having nitriding ability in the annealing atmosphere of the core formed by lamination is less than 30% by volume ratio. The strain relief annealing method for a laminated core according to any one of (1) to ( 3 ), wherein:
( 6 ) Any one of ( 1 ) to ( 5 ), wherein an inert gas such as He or Ar is added to the annealing atmosphere to adjust the oxidation degree and / or the nitriding gas concentration of the atmosphere. The strain relief annealing method of the laminated core as described in 2.
( 7 ) The non-oxidizing or reducing atmosphere in the annealing is composed of an inert gas and / or hydrogen and an inevitable mixed gas, ( 1 ) to ( 6 ), A method for strain relief annealing of laminated cores.
( 8 ) The distortion of the laminated core according to any one of (1) to ( 7 ), wherein the non-oriented electrical steel sheet used for forming the laminated core is a steel sheet having a crystal grain size of 50 μm or less. Removal annealing method.
( 9 ) The laminated core according to any one of (1) to ( 7 ), wherein the non-oriented electrical steel sheet used for forming the laminated core is a steel sheet that is not subjected to finish annealing after the final cold rolling. The strain relief annealing method.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in detail below.
The feature of the present invention is that the annealing performed after the core is formed is performed at a temperature of 800 ° C. or higher, preferably 850 ° C. or higher, which is higher than about 750 ° C. which is conventionally performed. The greatest effect of such conditions is that iron loss can be further improved, particularly in a low magnetic field, because recrystallization and work strain release are further promoted by high-temperature annealing. This tendency is particularly effective for higher-grade products, that is, for materials that increase the effect of suppressing recrystallization by increasing the amount of added elements and require large energy to restore processing strain.
[0010]
Conventionally, for non-oriented electrical steel sheets premised on core annealing, a technique for promoting recrystallization in subsequent strain relief annealing by performing skin pass rolling after finish annealing is known. If the core distortion removal annealing method is used, sufficient iron loss characteristics can be obtained even if such skin pass rolling is omitted. Furthermore, the recrystallization promotion effect can be further enhanced by combining the skin pass rolling and the strain relief annealing method according to the present invention.
[0011]
In order to obtain the above effects, it is necessary to carry out at a temperature of 800 ° C. or higher, desirably 850 ° C. or higher. For example, even if the temperature is as low as about 750 ° C. in the conventional method, recrystallization proceeds if sufficient annealing time is applied, but the necessary time increases exponentially as the temperature is lowered, which is not industrially preferable.
Furthermore, by performing core annealing at a high temperature according to the present invention, the optimum iron loss in the component system can be obtained regardless of crystal grain growth in continuous annealing. Furthermore, even when the core is formed using a material that is not subjected to final finish annealing, the iron loss can be greatly improved. In this way, the degree of annealing in the continuous annealing process can be freely selected, so that consideration of equipment for performing continuous annealing at a high temperature is omitted, operation costs are reduced, and punching processing for core formation is performed. It can be aimed at improving productivity. Normally, in the punching process of non-oriented electrical steel sheets, sufficient grain growth by annealing will soften the steel sheet, which is effective for extending the life of the punching dies, but grain growth must be done completely. The steel plate is hard and difficult to extend, which is rather preferable for obtaining dimensional accuracy at the time of punching and automatic caulking. In the past, the component system was determined according to the required magnetic properties, and as a result, the workability of the steel sheet was naturally defined. However, when using the strain relief annealing method of the laminated core according to the present invention, the punching workability is rather appropriate. It is possible to perform continuous annealing at such a temperature as to make a new material and perform recrystallization so as to compensate for it by annealing after core processing.
[0012]
There is no specific upper limit on the annealing temperature. In general, the higher the temperature, the easier the magnetic properties are improved and the annealing time can be shortened, but the fuel cost per hour increases. In addition, the higher the temperature is, the more easily the breakdown and nitridation of the insulating film proceeds, so it is necessary to limit them. More preferred conditions are between 880 and 970 ° C.
Also, the annealing time is not particularly specified. If heating is performed to the temperature of the present invention even in a very short time, recrystallization and release of processing strain proceed and iron loss is improved. However, this temperature needs to be reached in all parts of the core, and therefore it is necessary to take sufficient time depending on the characteristics of the annealing equipment, the size of the core, and the like. On the other hand, the upper limit is not particularly defined from the viewpoint of improving the iron loss, but the cost is increased as the operation is continued for a long time, whereas the effect of improving the iron loss is saturated in several hours at the longest. Moreover, since there is a concern about the deterioration of the insulating coating, it is limited. Usually, the soaking temperature is kept for 2 to 10 hours, and the heating and cooling times are combined for about 20 hours.
[0013]
Further, when the material to be transformed to the γ-phase is transformed once heated above the A 1 transformation point, carbides, can be re-dissolved and precipitation coagulation substances that inhibit grain growth, such as sulfides, recrystallization promotion It is effective on the above. However, in this case, since it is necessary to secure a recrystallization time after returning to the α phase at a certain level or more, the cooling rate from the Ar 3 transformation point to 650 ° C. needs to be a certain level or less. This speed needs to be 50 ° C./sec or less on average. The conditions for the material that causes the γ transformation are preferably included as components of approximately Si ≦ 2.5 wt%, Al ≦ 1.0 wt%, and (Si + 2Al) ≦ 2.5 wt%.
[0014]
There are two reasons why core annealing at a relatively high temperature as in the present invention has not been performed conventionally. One is the risk of destruction of the insulating coating and the oxidation of the steel sheet surface, and the other is the formation of AlN by nitriding of a material containing a certain amount of Al to inhibit recrystallization.
In order to prevent burnout of the insulating coating and oxidation of the steel sheet surface, it is necessary to carry out in a non-oxidizing or reducing atmosphere as an atmosphere for core annealing. If it contains more than a certain amount of an oxidizing atmosphere, that is, oxygen, moisture, or a gas that releases these by thermal decomposition, the insulation coating will be destroyed, and an oxide will be formed on the steel sheet surface to pin the steel. Causes iron loss deterioration.
[0015]
As the atmospheric gas used, a combustion gas containing N 2 , CO, and CO 2 as main components is often used. That is, the fuel is burned to heat the core, and the exhaust gas dried by the heat is heated and blown into the furnace. The moisture content of the combustion exhaust gas is about 55 ° C. (about 16 vol%) as a dew point. This gas is cooled and dried to obtain a dew point of about 15 ° C. (about 1.7 vol%). In the case of an inorganic coating mainly composed of chromic acid or the like with core annealing at a relatively low temperature of the prior art, there is no particular problem if the moisture content is as described above, but when annealing at a high temperature as in the present invention The oxidation reaction is easy to proceed and the effect on quality is very large. In order to avoid this, an extremely low oxidizing gas such as an isolated gas such as N 2 , H 2 , Ar, or a decomposition gas of ammonia (H 2 : N 2 = 3: 1) is mixed to be substantially It is advisable to lower the typical oxygen potential (PH 2 O / PH 2 ). For example, if the gas has a dew point of 15 ° C., 17% or more of hydrogen is mixed and PH 2 O / PH 2 is made 0.1 or less, so that almost no deterioration can be seen with an inorganic coating made of phosphate. . However, in the case of a film containing an organic substance such as a resin, it is necessary to further reduce the oxygen potential to prevent oxidation. In such a case, the core to be annealed is covered to block the atmosphere from the outside air, and a specific gas with high purity is used. Also in this case, an inert gas or hydrogen is appropriately mixed, or these gases are used as a main component, whereby the oxygen potential can be further reduced and deterioration of the film can be more effectively suppressed.
[0016]
Further, for the generation of AlN by nitriding, it is necessary to reduce the gas having nitriding ability from the atmospheric gas. Since the gist of the present invention is to promote recrystallization in the core, factors that inhibit recrystallization must be eliminated as much as possible. Usually, Al is added to improve magnetic properties, and the amount is about 1% in a high grade. On the other hand, N is usually suppressed to 0.01% or less at the steelmaking stage to suppress AlN generation. However, a material containing 0.1% or more of Al absorbs nitrogen in the atmospheric gas and forms AlN in the subsequent heat treatment. In particular, since core annealing is longer in annealing time than continuous annealing, the amount of nitriding tends to increase, and when annealing is performed at a high temperature as in the present invention, nitriding is further facilitated.
[0017]
From the above, when the steel sheet contains 0.1 wt% or more of Al as the annealing atmosphere of the present invention, the ratio of the gas having nitriding ability is defined as less than 30% by volume. This is a limiting value in the case when the target gas and nitrogen, as ammonia and NO x, in particular for high gas nitriding ability to the steel sheet, it needs to limit its content to less than 0.1% There is. Note that when the Al content is less than 0.1%, the nitriding of the steel plate hardly occurs, and the amount of AlN produced does not hinder the effects of the present invention. Is not necessary.
[0018]
The composition and manufacturing method of the non-oriented electrical steel sheet used in the present invention are not particularly limited. In general, the grades of non-oriented electrical steel sheets are determined by the iron loss and saturation magnetic flux density determined by the process conditions such as the amount of additive elements, finish annealing temperature, hot rolling, cold rolling, etc. Appropriate materials are selected. The strain relief annealing method for a laminated core according to the present invention brings about an iron loss improvement effect over that of the conventional method for almost all grades.
[0019]
The components in steel added to the non-oriented electrical steel sheet used in the present invention include the following.
Si is an important element that increases the specific resistance and lowers the iron loss, but if it is too much, the workability deteriorates. Usually, 5% or less is added.
Al is also an important element that increases the specific resistance and lowers the iron loss, but if it is too much, the workability deteriorates. Usually, 2% or less is added.
[0020]
If C is present above a certain level, it causes magnetic aging during use as a core of electrical equipment and deteriorates magnetic properties, so it is necessary to limit it to 0.01% or less. In addition to adjusting the content at the molten steel stage, a method of decarburizing in a weakly oxidizing atmosphere by continuous finish annealing is also used.
If N is large, it will combine with Al to form AlN and inhibit grain growth, so it is necessary to limit it to 0.01% or less at the molten steel stage.
[0021]
S is inevitably mixed in the molten steel stage, but if it is too much, it binds with Mn and precipitates at the grain boundary to inhibit recrystallization, so it is necessary to limit it to 0.01% or less.
In addition, Mn, P, B, Ni, Cr, Sb, Sn, Cu, etc. are contained for the purpose of improving magnetic properties, workability, and weather resistance. The amount of addition is determined according to the characteristics of the target steel sheet.
[0022]
Continuous casting slabs or steel ingots composed of the above components are hot-rolled, cold-rolled twice or more with one or intermediate annealing, finish-annealing, insulating coating is baked and applied, and non-directional electromagnetic Finish on a steel plate. In this step, it is possible to omit hot rolling as a thin slab equivalent to a hot rolled plate by continuous casting. Further, for the purpose of improving the magnetic characteristics, the hot-rolled sheet may be annealed, or self-annealing may be performed by increasing the coiling temperature after hot rolling.
[0023]
By appropriately selecting the above component system and manufacturing method, the iron loss of the steel sheet can be made extremely small. The strain relief annealing method according to the present invention further reduces this iron loss. Moreover, a favorable iron loss characteristic can also be acquired using a cheaper steel plate. That is, even if the material is designed to reduce costs by lowering or omitting the finish annealing temperature, it is lower than that obtained by the conventional method by applying strain relief annealing according to the present invention after forming the core. It is possible to obtain iron loss characteristics.
[0024]
【Example】
<Example 1>
A core is formed using a non-oriented electrical steel sheet having a thickness of 0.5 mm manufactured by the components and manufacturing methods shown in Table 1, and the core is formed in three types of atmospheres including combustion gas, nitrogen + hydrogen, and hydrogen only. Then, annealing was performed at a soaking temperature of 750 to 950 ° C. and a soaking time of 2 hours. The results of iron loss (W 15/50 ) are shown in Table 2, and the state of the insulating coating is shown in Table 3.
[0025]
In the materials C and D in which the Al content is less than 0.1%, the iron loss is improved as the annealing temperature is higher regardless of the atmosphere composition, whereas in the materials A and B containing 0.3% Al, In an atmosphere containing nitrogen, the iron loss deteriorated at 900 ° C. or higher.
As for the state of the insulating coating, when only hydrogen was used as the atmospheric gas, almost no deterioration was observed up to 950 ° C. for all materials, and no deterioration was observed up to 900 ° C. even for the hydrogen + nitrogen mixed gas. On the other hand, with the combustion gas, the coating film was significantly deteriorated at 850 ° C. or higher.
[0026]
[Table 1]
[Table 2]
[Table 3]
<Example 2>
The non-oriented electrical steel sheets of B in Table 1 were punched into a predetermined shape and laminated to form a core. This core was annealed under the atmospheric conditions shown in Table 4 at a soaking temperature of 900 ° C. for 2 hours. Table 4 shows the iron loss (W 15/50 ) and the state of the insulating coating.
The magnetic properties were hardly improved by annealing under the conditions of Nos. 1, 2, 3, 4 and 6 containing nitrogen or ammonia in a certain amount or more in the atmosphere.
[0030]
Also, the coating conditions were Nos. 5 and 6 with a lot of hydrogen in the atmosphere, and particularly those with little deterioration were obtained.
[0031]
[Table 4]
<Example 3>
Non-oriented electrical steel sheets manufactured by the component system and manufacturing method shown in Table 5 were punched into a predetermined shape and laminated to form a core. The core was annealed in an atmosphere of 99% hydrogen at a soaking temperature of 900 ° C. for 2 hours. Table 6 shows the crystal grain size and iron loss (W15 / 50) before and after annealing.
[0033]
Even when a material having a crystal grain size of 50 μm or less before core annealing is used, the core annealing method of the present invention can be used to achieve 100 to 150 μm with good magnetic properties. In particular, with the material e, it was possible to obtain almost the same magnetic characteristics as those obtained without performing the finish annealing.
[0034]
[Table 5]
[Table 6]
【The invention's effect】
As described above, by using the method for removing strain of a laminated core according to the present invention, even if the continuous annealing process and the subsequent skin pass are simplified or omitted, the magnetic characteristics of the core such as a motor are remarkably improved, and It becomes possible to improve the workability when processing the core.
Claims (9)
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|---|---|---|---|
| JP13683598A JP3993689B2 (en) | 1998-05-19 | 1998-05-19 | Strain relief annealing method for laminated core |
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|---|---|---|---|
| JP13683598A JP3993689B2 (en) | 1998-05-19 | 1998-05-19 | Strain relief annealing method for laminated core |
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| JP3993689B2 true JP3993689B2 (en) | 2007-10-17 |
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| WO2013111726A1 (en) | 2012-01-25 | 2013-08-01 | 新日鐵住金株式会社 | Metal member annealing method |
| JP6697902B2 (en) | 2016-02-26 | 2020-05-27 | 株式会社三井ハイテック | Tray and heat treatment method |
| JP7328522B2 (en) * | 2019-08-06 | 2023-08-17 | 日本製鉄株式会社 | motor core |
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