JP4337146B2

JP4337146B2 - Method for producing non-oriented electrical steel sheet

Info

Publication number: JP4337146B2
Application number: JP22727197A
Authority: JP
Inventors: 昭日裏; 伸夫山上; 善彦尾田; 義彦小野; 靖田中
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 1997-08-08
Filing date: 1997-08-08
Publication date: 2009-09-30
Anticipated expiration: 2017-08-08
Also published as: JPH1161257A

Description

【０００１】
【発明が属する技術分野】
本発明は、鉄損が低く且つ磁気異方性の小さい無方向性電磁鋼板の製造方法に関する。
【０００２】
【従来の技術】
無方向性電磁鋼板は各種モータの鉄心材料として大量に使用されており、磁気特性として磁束密度と鉄損が重視される。無方向性電磁鋼板はフルプロセス材とセミプロセス材とに分けられる。このうちフルプロセス材は鉄鋼メーカー側の仕上焼鈍により所定の磁気特性を得るものである。一方、セミプロセス材は需要家において打抜き加工後に歪取り焼鈍を行うことにより、所定の磁気特性を得るものであり、このセミプロセス材では、歪取り焼鈍時に加工歪みの除去と同時に結晶粒も成長することから、より一層の低鉄損化が可能となる。このため歪取り焼鈍は磁性焼鈍とも呼ばれている。
【０００３】
従来、Ｓｉ量が１ｗｔ％以下の低Ｓｉ電磁鋼板は、磁性焼鈍を実施しない状態で使用される場合が多かったが、近年では、素材コストの低減化や電気機器の高効率・省エネルギー化の要請から、磁性焼鈍による低鉄損化によりグレードアップさせて使用する比率が年々増加している。
【０００４】
一般に鋼板中に微細な析出物が存在すると、仕上焼鈍時や磁性焼鈍時の粒成長が阻害されて低鉄損化を図ることができない。このような析出物の中でも、Ｓｉ：１．５ｗｔ％以下の低Ｓｉ電磁鋼板では微細なＭｎＳ、ＡｌＮ、酸化物が特に粒成長を阻害し、鉄損を大幅に劣化させることが知られている。したがって、このような析出物による影響を抑え、鋼板の粒成長性を向上させるには、析出物量を大幅に低減するか或いは析出物を粗大化させて無害化することが有効である。
析出物量の低減化には、Ｎ、Ｓ等の析出物形成元素を低減する必要があるが、このためには２次精練工程での脱硫、脱窒の強化、長時間の脱ガス処理が必要となり、製鋼コストの上昇が避けられない。
【０００５】
一方、析出物の粗大化方法としては、スラブ加熱温度の低温化に関する技術が提案されている。例えば、特公昭５０−３５８８５号公報には、Ｓｉ：３．５ｗｔ％以下、Ａｌ：１ｗｔ％以下のスラブを１２００℃以下に加熱することによりＡｌＮを粗大に析出させる技術が、また特公平７−４２５０１号公報には、Ｓｉ：１．５ｗｔ％以下、Ａｌ：０．５ｗｔ％以下、Ｓ：０．００５０ｗｔ％以下のスラブを１１００℃以下に加熱することで熱間圧延中のＭｎＳの微細析出を防止する技術が、それぞれ開示されている。
【０００６】
【発明が解決しようとする課題】
しかし、このように単純にスラブ加熱温度を低温化するだけでは、微細析出物の無害化には限界があり、十分な磁気特性は得られない。近年、需要家において行われる磁性焼鈍は益々低温・短時間化する傾向にあり、優れた磁気特性を有する無方向性電磁鋼板を得るためには、より一層の微細析出物の無害化が必要となる。
【０００７】
近年、スラブ加熱や保熱を伴わない直送圧延に関する技術が提案され、例えば、特開平１−２２５７２６号公報には、Ｓｉ：１．５ｗｔ％以下を含有するスラブの直送圧延において、粗圧延後に９５０℃以上の温度域にて３０秒以上加熱することによりＡｌＮのサイズを粗大化させる技術が示されている。また特開平８−７３９３９号公報では、磁束密度向上のためにＳｂ，Ｓｎ，Ｃｕ等を添加したスラブの熱間圧延において、粗圧延後に表面温度９３０℃以上の温度域に６０秒以上保持する技術が示されている。直送圧延ではスラブを室温付近まで冷却させないために、析出物は微細化する傾向にあり、このため上記の各技術では粗圧延後の一定時間保持により析出物を粗大化させている。したがって、これらの技術により得られる鋼板の磁気特性は、従来一般のスラブ加熱材（常温スラブを再加熱して熱間圧延した材料）と同レベル程度の特性でしかない。
【０００８】
ところで、回転機鉄心向けの電磁鋼板については、従来、ＪＩＳ−Ｃ２５５０法のようなコイル長手方向とコイル直角方向の平均磁気特性よりも、全周方向の磁気特性が優れていることが重視されている。この全周方向特性は実際の励磁状態に近いリング状試料で評価され、磁気異方性が小さく、板面のあらゆる方向の平均値の磁気特性が均一であることが求められる。
【０００９】
例えば、特開昭５９−１２３７１５号公報や特公平６−１０４８６５号公報等には、リング状試料で測定しても良好な磁気特性が得られる無方向性電磁鋼板の製造方法が提案され、このうち特開昭５９−１２３７１５号公報では、Ｓｉ：４．０ｗｔ％以下、Ａｌ：１．０ｗｔ％以下の組成のスラブを熱間圧延した後の巻取温度を７００〜９５０℃とし、自己焼鈍により熱延板の結晶粒度を粒度番号４以下とした上で、圧下率８５％以上の強圧下冷延を行う方法が記載されている。しかし、この技術でも熱延板の結晶粒を安定的に粗大化することが難しく、さらに圧下率８５％以上の強圧下冷延を必要とするため熱延板の板厚が４〜５ｍｍとなり、冷間圧延機のミルパワーの観点から実現するのは難しい。
【００１０】
以上のように、従来技術により製造される無方向性電磁鋼板の磁気特性は決して満足できるものではなく、このため微細析出物のより一層の低減化が図られ、リング状試料でも良好な磁気特性が得られるような低Ｓｉ電磁鋼板を安価に且つ安定して製造することができる新たな技術の開発が望まれていた。
したがって本発明の目的は、このような従来技術の課題を解決し、粒成長を阻害する微細析出物を極力無害化して、鉄損が低く且つ磁気異方性の小さい無方向性電磁鋼板を安定して製造することができる方法を提案することにある。
【００１１】
【課題を解決するための手段】
本発明者らは、低鉄損で且つ磁気異方性が小さい低Ｓｉ電磁鋼板の製造方法について検討を加え、その結果、特定の組成の連続鋳造スラブの熱間圧延工程において、▲１▼スラブ加熱温度を特定の低温領域とした上で、▲２▼スラブを特定の範囲の累積圧下率で粗圧延し、引き続き、▲３▼この粗圧延材をオンラインにて加熱して粗圧延終了温度よりも２０℃以上高く且つスラブ加熱温度以下の温度に昇温させた後、仕上圧延を行う、という一連の製造条件を採ることにより、さらに好ましくは、その際の仕上温度および巻取温度を適正化することにより、鉄損が効果的に低減し、且つ磁気異方性も小さくなることを見い出した。
【００１２】
本発明はこのような知見に基づきなされたもので、その特徴は以下の通りである。
［1］Ｃ：０．００５ｗｔ％以下、Ｐ：０．２ｗｔ％以下、Ｎ：０．００１７〜０．００５ｗｔ％、Ｓｉ：０．１ｗｔ％以上１．５ｗｔ％未満、Ｍｎ：０．２〜０．５ｗｔ％、Ｓ：０．００５０〜０．０２ｗｔ％、Ｓｏｌ．Ａｌ：０．００４ｗｔ％以下または０．１〜０．４ｗｔ％、残部Ｆｅおよび不可避不純物からなる組成の連続鋳造スラブを、９５０〜１１５０℃に加熱して累積圧下率７５％以上の粗圧延を施し、引き続き該粗圧延材をオンラインにて加熱して粗圧延終了温度よりも２０℃以上高く且つスラブ加熱温度以下の温度に昇温させた後、仕上圧延を行い、次いで脱スケール、冷間圧延および焼鈍することを特徴とする無方向性電磁鋼板の製造方法。
【００１３】
［2］上記［1］の製造方法において、熱延仕上温度を［Ａｒ_１変態点＋２０］℃以上とし、巻取温度を６４０〜７５０℃とすることを特徴とする無方向性電磁鋼板の製造方法。
【００１４】
【発明の実施の形態】
以下、本発明の詳細をその限定理由とともに説明する。
本発明では、特定の成分組成の連続鋳造スラブを素材とし、これを熱間圧延する際に、スラブを９５０〜１１５０℃に加熱して累積圧下率７５％以上の粗圧延を施し、引き続き該粗圧延材をオンラインにて加熱して粗圧延終了温度よりも２０℃以上高く且つスラブ加熱温度以下の温度に昇温させた後、仕上圧延を行い、次いで脱スケール、冷間圧延および焼鈍を行う。
【００１５】
先ず、スラブ加熱温度が鉄損に及ぼす影響を調査するため、以下のような試験を行った。
Ｃ：０．００２５ｗｔ％、Ｓｉ：０．１５ｗｔ％、Ｍｎ：０．４０ｗｔ％、Ｐ：０．０９０ｗｔ％、Ｓ：０．００５０ｗｔ％、Ｓｏｌ．Ａｌ：０．００１２ｗｔ％、Ｎ：０．００２５ｗｔ％、Ｔ．Ｏ：０．０１０ｗｔ％の組成の鋼を溶製し、これを鋳造して厚さ２２０ｍｍのスラブを作製した。このスラブを常温から９５０〜１２５０℃に１時間加熱した後、板厚３０ｍｍまで粗圧延し、引き続き加熱処理を施すことなく板厚２．３ｍｍまで仕上圧延した。次いで、この熱延板を酸洗した後、板厚０．５ｍｍまで冷間圧延し、さらに７５０℃×１分間の仕上焼鈍を施した。
【００１６】
このようにして得られた各鋼板の鉄損を２５ｃｍエプスタイン試験片を用いて測定し、スラブ加熱温度と仕上焼鈍後の鉄損との関係を調べた。その結果を図１に○印で示す。同図によれば、スラブ加熱温度を低くすることにより鉄損が低下することが判る。これは低温域でのスラブ加熱によりスラブ加熱時のＭｎＳの再溶解量が低減し、熱間圧延時の微細析出が抑制される結果、粒成長性が向上するためであると考えられる。
【００１７】
次に、粗圧延後に加熱処理を行った場合のスラブ加熱温度と鉄損との関係を調査するため、以下のような試験を行った。
上記試験で用いたスラブと同じ組成のスラブを常温から９５０〜１２５０℃に１時間加熱した後、板厚３０ｍｍまで粗圧延し、直ちにこの粗圧延材を加熱して粗圧延終了温度よりも４０℃高い温度に昇温（粗圧延終了温度に対する昇温量ΔＴ：４０℃）させた後、板厚２．３ｍｍまで仕上圧延した。次いで、この熱延板を酸洗した後、板厚０．５ｍｍまで冷間圧延し、さらに７５０℃×１分間の仕上焼鈍を施した。なお、加熱処理前の粗圧延材の温度（粗圧延終了温度）は９００℃とした。
このようにして得られた各鋼板の鉄損を２５ｃｍエプスタイン試験片を用いて測定し、スラブ加熱温度と仕上焼鈍後の鉄損との関係を調べた。その結果を図１に●印で示す。
【００１８】
図１によれば、粗圧延後に加熱処理を行った鋼板は加熱処理を行わない鋼板に較べて鉄損が低下し、その効果は特にスラブ加熱温度１１５０℃以下の鋼板において顕著であることが判る。このように粗圧延後に加熱処理を行うことにより鉄損が顕著に低下する理由は必ずしも明確ではないが、以下のような理由が考えられる。すなわち、粗圧延により加工歪みが導入され、ＭｎＳの析出に必要なエネルギーが下がった状態の粗圧延材にオンラインで加熱処理を行うことにより、鋼中に固溶しているＭｎＳの析出核の歪誘起成長が生じ、この核を起点として粗圧延直後または仕上圧延の前段においてＭｎＳの粗大化が進行するためであると考えられる。加えて、この加熱処理によりγ粒径も大きくなるため、仕上焼鈍後の粒径も大きくなるものと考えられる。一方、粗圧延後に加熱処理を行わない鋼板では、析出核の歪誘起成長が進展しにくくなるために仕上圧延時にＭｎＳが微細に析出し、粒成長性が低下したものと考えられる。
【００１９】
また、粗圧延後の加熱処理による低鉄損化がスラブ加熱温度１１５０℃超の鋼板において十分に得られない原因は、スラブ加熱温度の上昇に伴い粗圧延時の温度域も高温となるため、粗圧延時において加工歪みが有効に導入されず、このため粗圧延後に加熱処理を行っても析出核の歪み誘起成長が十分に生じないためであると考えられる。
以上の理由から本発明では、スラブを常温から加熱する際のスラブ加熱温度を、粗圧延後の加熱処理により鉄損が顕著に低下する温度領域である１１５０℃以下とする。一方、スラブ加熱温度が９５０℃未満では仕上圧延が困難になるため、スラブ加熱温度の下限は９５０℃とする。
【００２０】
次に、粗圧延後の加熱処理による昇温量ΔＴが鉄損に及ぼす影響を調査するため、以下のような試験を行った。
Ｃ：０．００２５ｗｔ％、Ｓｉ：０．１５ｗｔ％、Ｍｎ：０．３５ｗｔ％、Ｐ：０．０９０ｗｔ％、Ｓ：０．００５０ｗｔ％、Ｓｏｌ．Ａｌ：０．００１３ｗｔ％、Ｎ：０．００３０ｗｔ％、Ｔ．Ｏ：０．０１０ｗｔ％の組成の鋼を溶製し、これを鋳造して厚さ２２０ｍｍのスラブを作製した。このスラブを１０８０℃に１時間加熱した後、板厚３０ｍｍまで粗圧延した。この粗圧延材の温度（粗圧延終了温度）は９０５℃であった。引き続きこの粗圧延材をソレノイド式誘導加熱装置により加熱して９１０℃〜１０５５℃（粗圧延終了温度に対する昇温量：５〜１５０℃）に昇温させた後、仕上圧延を行った。次いで、この熱延板を酸洗した後、板厚０．５ｍｍまで冷間圧延し、さらに７５０℃×１分間の仕上焼鈍を施した。
【００２１】
このようにして得られた各鋼板の鉄損を２５ｃｍエプスタイン試験片を用いて測定し、粗圧延後の加熱処理による昇温量ΔＴ（粗圧延終了温度に対する昇温量。以下同様）と仕上焼鈍後の鉄損との関係を調べた。その結果を図２に示す。同図によれば、粗圧延後の加熱処理による昇温量ΔＴが２０℃以上になると鉄損の低減効果が大きくなっている。
以上の理由から本発明では、粗圧延に引き続き、粗圧延材を加熱して粗圧延終了温度よりも２０℃以上高い温度に昇温させた後、仕上圧延を行うものとする。但し、粗圧延後の加熱温度がスラブ加熱温度を超えると析出物の再溶解が進んで粒成長性が低下するため、粗圧延後の加熱温度はスラブ加熱温度以下とする。
【００２２】
次に、粗圧延の累積圧下率が鉄損に及ぼす影響を調査するため、以下のような試験を行った。
Ｃ：０．００２５ｗｔ％、Ｓｉ：０．１５ｗｔ％、Ｍｎ：０．３５ｗｔ％、Ｐ：０．１００ｗｔ％、Ｓ：０．００６０ｗｔ％、Ｓｏｌ．Ａｌ：０．００１２ｗｔ％、Ｎ：０．００３０ｗｔ％、Ｔ．Ｏ：０．０１０ｗｔ％の組成の鋼を溶製し、これを鋳造して厚さ３００ｍｍ、２５０ｍｍ、２２０ｍｍ、１５０ｍｍ、１２０ｍｍ、１００ｍｍ、８０ｍｍの各スラブを作製した。これらのスラブを１１００℃に１時間加熱した後、板厚３０ｍｍまで粗圧延した。この粗圧延材の温度は８９０℃であった。引き続きこの粗圧延材をソレノイド式誘導加熱装置により加熱して９３０℃（粗圧延終了温度に対する昇温量：４０℃）に昇温させた後、仕上げ圧延を行った。次いで、この熱延板を酸洗した後、板厚０．５ｍｍまで冷間圧延し、さらに７５０℃×１分間の仕上焼鈍を施した。
【００２３】
このようにして得られた各鋼板の鉄損を２５ｃｍエプスタイン試験片を用いて測定し、粗圧延の累積圧下率と仕上焼鈍後の鉄損との関係を調べた。その結果を図３に示す。同図によれば、粗圧延での累積圧下率を７５％以上とすることにより鉄損が効果的に低下することが判る。これに対し、粗圧延での累積圧下率が７５％未満では、ＭｎＳの析出に必要な駆動力を下げるための歪みエネルギーの導入が不十分であるため、ＭｎＳの粗大化が起こりにくくなり、鉄損は高くなる。
このため本発明では、粗圧延の累積圧下率の下限を７５％とする。なお、累積圧下率の上限は粗圧延機のミルパワーで決まるため、特に規定しない。
【００２４】
次に、熱延仕上温度と巻取温度の影響について検討した結果、スラブを９５０〜１１５０℃に加熱して累積圧下率７５％以上の粗圧延を施し、引き続き粗圧延終了温度よりも２０℃以上高く且つスラブ加熱温度以下の温度に加熱昇温させた粗圧延材に対して、熱延仕上温度と巻取温度を適正化することにより磁気異方性をより小さくできることが判った。
【００２５】
先ず、熱延仕上温度が磁気異方性に及ぼす影響を調査するため、以下のような試験を行った。
Ｃ：０．００２５ｗｔ％、Ｓｉ：０．１５ｗｔ％、Ｍｎ：０．４０ｗｔ％、Ｐ：０．０９０ｗｔ％、Ｓ：０．００６０ｗｔ％、Ｓｏｌ．Ａｌ：０．００１２ｗｔ％、Ｎ：０．００２５ｗｔ％、Ｔ．Ｏ：０．０１０ｗｔ％の組成の鋼を溶製し、これを鋳造して厚さ２２０ｍｍのスラブを作製した。このスラブを１１００℃に１時間加熱した後、板厚３０ｍｍまで粗圧延し、引き続きこの粗圧延材をソレノイド式誘導加熱装置により加熱して９４０℃（粗圧延終了温度に対する昇温量ΔＴ：４０℃）に昇温させた後、板厚２．３ｍｍまで仕上圧延を行った。この際、仕上温度は９２０〜７８０℃とし、巻取温度は６７０℃とした。次いで、この熱延板を酸洗した後、板厚０．５ｍｍまで冷間圧延し、さらに７５０℃×１分間の仕上焼鈍を行った。なお、使用した鋼の変態点を測定したところ、Ａｒ₃変態点：８７０℃、Ａｒ₁変態点：８１０℃であった。
【００２６】
各鋼板コイルから外径４５ｍｍ、内径３３ｍｍのリング試験片を切り出し、これを５枚積層させて磁気特性の評価を行い、熱延仕上温度とリング状試料の鉄損との関係を調べた。その結果を図４に示す。
図４によれば、熱延仕上温度が［Ａｒ₁変態点＋２０］℃以上になると、リング状試料で測定した鉄損は低くなり、Ａｒ₃変態点以上ではさらに低下する傾向がある。これは上記の温度以上で熱間圧延を終了することにより集合組織がランダム化し、これにより磁気異方性が小さくなるためであると考えられる。
したがって本発明では、熱延仕上温度を［Ａｒ₁変態点＋２０］℃以上、望ましくはＡｒ₃変態点以上とすることが好ましい。
【００２７】
次に、熱延巻取温度が磁気異方性に及ぼす影響を調査するため、以下のような試験を行った。
上記試験で用いたスラブと同じ組成のスラブを同様の条件で粗圧延および粗圧後加熱処理し、引き続きこの粗圧延材を仕上温度８４０℃で板厚２．３ｍｍに仕上圧延した後、巻取温度６００〜７５０℃で巻き取った。次いで、この熱延板を酸洗した後、板厚０．５ｍｍまで冷間圧延し、さらに７５０℃×１分の仕上焼鈍を行った。
各鋼板コイルから外径４５ｍｍ、内径３３ｍｍのリング試験片を切り出し、これを５枚積層させて磁気特性の評価を行い、熱延巻取温度とリング状試料の鉄損との関係を調べた。その結果を図５に示す。
【００２８】
図５によれば、巻取温度が６４０℃未満ではリング状試料の鉄損は高くなっている。また、６４０℃未満の巻取温度では熱延板のフェライト粒径も小さくなるため、磁束密度の低下を招く。
したがって本発明では、巻取温度を６４０℃以上とすることが好ましい。但し、巻取温度が過剰に高いと熱延板のスケール厚さの増大による酸洗性低下やコイル内での特性のばらつきが大きくなることから、巻取温度は７５０℃を上限とすることが好ましい。
【００２９】
次に、本発明における鋼組成の限定理由について説明する。
Ｃは磁気時効の原因となり磁気特性を劣化させるため、０．００５ｗｔ％以下とする。
Ｐは鋼板の硬度を高め、打ち抜き加工性を向上させる作用があるが、過剰な添加は冷間圧延性の劣化を招くため、０．２ｗｔ％以下とする。
Ｓｉは添加量の増大とともに鉄損を低減させる元素であり、鉄損低減のためには０．１ｗｔ％以上添加する必要があるが、１．５ｗｔ％以上となると磁束密度が低下する。このためＳｉ量は０．１ｗｔ％以上、１．５ｗｔ％未満とする。
【００３０】
Ｍｎは、その添加量の増大に伴いスラブ加熱時に再溶解するＭｎＳ量が低減し、熱間圧延時に微細析出するＭｎＳが少なくなるため粒成長性は向上する。この傾向はＭｎ量が約０．５ｗｔ％までは顕著であり、また、電気抵抗も増大することから低鉄損化に有利である。しかし、０．５ｗｔ％を超えるようなＭｎの過剰な添加はコスト上昇を招く。一方、Ｍｎ量が０．２ｗｔ％未満では、スラブ加熱時に再溶解するＭｎＳ量が増大して熱間圧延時に微細析出するＭｎＳが多くなる。このため粗圧延後の加熱処理を行っても、特に磁性焼鈍後の粒成長性が確保できなくなる。このためＭｎ量は０．２〜０．５ｗｔ％とする。
【００３１】
ＳはＭｎと結合してＭｎＳとして微細析出し、粒成長を阻害するので可能な限り低減することが望ましいが、本発明ではこのＭｎＳをある程度無害化できるためＳ量は０．０２ｗｔ％を上限とすればよく、したがって、Ｓ量は０．０２ｗｔ％以下とする。
本発明は上記のような範囲のＳ含有量を許容するが、本発明はこのような範囲において特にＳ含有量が高めの領域においてより有効に機能する。鋼板のＳ含有量と本発明の効果との関係を調べるため、以下のような試験を行った。
【００３２】
Ｃ：０．００３ｗｔ％、Ｓｉ：０．１６ｗｔ％、Ｍｎ：０．３５ｗｔ％、Ｐ：０．０９０ｗｔ％、Ｐ：０．１００ｗｔ％、Ｓ：０．００５０〜０．０２２０ｗｔ％、Ｓｏｌ．Ａｌ：０．００１２ｗｔ％、Ｎ：０．００３０ｗｔ％の組成の鋼を溶製し、これを鋳造して厚さ２２０ｍｍのスラブを作製した。このスラブを１１００℃に１時間加熱した後、板厚３０ｍｍまで粗圧延した。引き続きこの粗圧延材をソレノイド式誘導加熱装置により加熱して粗圧延終了温度よりも４０℃高い温度に昇温させた後、仕上圧延を行った。また、上記と同じ組成およびサイズのスラブについて、粗圧延後の加熱処理を行わない以外は上記と全く同じ条件で粗圧延および仕上圧延を行った。次いで、これらの熱延板を酸洗した後、板厚０．５ｍｍまで冷間圧延し、７５０℃×１分間の仕上焼鈍を行い、さらに７５０℃×２時間の磁性焼鈍を行った。
【００３３】
このようにして得られた鋼板のＳ含有量と仕上焼鈍後および磁性焼鈍後の鉄損との関係を図６に示す。同図によれば、Ｓ含有量の増加とともに鉄損は増大しているが、粗圧延後の加熱処理を施した鋼板は、加熱処理を施さない鋼板に較べて鉄損の増大が大幅に抑制され、また、このような鉄損の低減化効果は特にＳ含有量が高めのほうが大きい。しかし、Ｓ含有量が０．０２ｗｔ％を超えると鉄損そのものが増大するだけでなく、加熱処理による鉄損の低減化効果も小さくなる。
Ｎは、その含有量が多いと窒化物の析出量が多くなり、磁性焼鈍時の粒成長性が低下して鉄損が増大する。このためＮ量は０．００５ｗｔ％以下とする。
【００３４】
Ｓｏｌ．Ａｌは、０．００４ｗｔ％超〜０．１ｗｔ％未満の微量添加の範囲ではＮと結合して微細なＡｌＮを形成するため粒成長性を著しく阻害し、磁気特性を劣化させる。一方、Ｓｏｌ．Ａｌが０．１ｗｔ％以上の添加範囲では、ＡｌＮが粗大になるため磁気特性は劣化せず、Ａｌは固有抵抗の上昇に寄与するが、０．４ｗｔ％を超えると磁束密度の低下を招く。このためＳｏｌ．Ａｌは０．００４ｗｔ％以下または０．１〜０．４ｗｔ％とする。
その他の元素として、磁気特性の改善を目的として、０．０５ｗｔ％以下のＳｂ、０．０５ｗｔ％以下のＳｎを添加することができる。
残部は実質的にＦｅからなり、不可避不純物元素等の少量の成分元素を含むことを妨げない。
【００３５】
本発明の製造方法では、上述した製造条件以外は特別な制約はなく、したがって、通常の製造条件を採用して構わない。すなわち、転炉で吹錬した溶鋼を脱ガス処理して所定の成分に調整した後、スラブに鋳造し、このスラブを上述した条件で熱間圧延する。また、熱間圧延後の熱延板焼鈍は行ってもよいが必須ではない。次いで、一回の冷間圧延若しくは中間焼鈍をはさんだ２回以上の冷間圧延により所定の板厚とした後、仕上焼鈍を行い、さらに必要に応じて磁性焼鈍を行う。
【００３６】
【実施例】
［実施例１］
転炉吹錬および脱ガス処理を経て表１に示す組成の鋼を溶製し、連続鋳造により厚さ２３０ｍｍのスラブとした。これらスラブを表２に示す条件で板厚２．３ｍｍまで熱間圧延した。この際の粗圧延終了温度は９００℃、仕上温度は８２０〜８５０℃、巻取温度は６５０〜６８０℃とした。次いで、この熱延コイルを酸洗し、板厚０．５ｍｍまで冷間圧延した後、表２に示す条件で仕上焼鈍（各焼鈍温度×１分間）を施し、次いで、７５０℃×２時間の磁性焼鈍を施した。
各鋼板の仕上焼鈍後および磁性焼鈍後の磁気特性を、２５ｃｍのエプスタイン試験片を用いて測定した。その結果を表２に併せて示す。
表２によれば、本発明例においては仕上焼鈍後および磁性焼鈍後の鉄損が低い無方向性電磁鋼板が得られることが判る。
【００３７】
【表１】

【００３８】
【表２】

【００３９】
［実施例２］
表１に示す鋼番１（Ａｒ₁変態点：８１０℃）、鋼番４（Ａｒ₁変態点：８４０℃）の鋼を溶製し、連続鋳造により厚さ２３０ｍｍのスラブとした。これらのスラブを１１００℃に加熱した後、板厚３２ｍｍまで粗圧延し、引き続きソレノイド式誘導加熱装置により加熱して粗圧延終了温度よりも３５℃高い温度に昇温させた後、表３に示す条件で仕上圧延を行い、板厚２．３ｍｍの熱延板とした。次いで、この熱延コイルを酸洗した後、板厚０．５ｍｍまで冷間圧延し、７５０℃×１分間の仕上焼鈍を施し、さらに７５０℃×２時間の磁性焼鈍を施した。
【００４０】
得られた各鋼板の仕上焼鈍後および磁性焼鈍後の磁気特性を、外径４５ｍｍ、内径３３ｍｍのリング試験片を用いて測定した。その結果を表３に併せて示す。
表３によれば、本発明の製造方法において特に熱延仕上温度と巻取温度を特定の範囲に制御することにより、仕上焼鈍後および磁性焼鈍後におけるリング状試料の鉄損が低い無方向性電磁鋼板が得られることが判る。
【００４１】
【表３】

【００４２】
【発明の効果】
以上述べたように本発明によれば、鉄損が低く且つ磁気異方性の小さい無方向静電磁鋼板を安定して製造することができる。
【図面の簡単な説明】
【図１】粗圧延後に加熱処理を施した材料と加熱処理を施さない材料について、スラブ加熱温度と仕上焼鈍後の鉄損との関係を示すグラフ
【図２】スラブを低温加熱した材料について、粗圧延後の加熱処理による昇温量ΔＴと仕上焼鈍後の鉄損との関係を示すグラフ
【図３】スラブを低温加熱し且つ粗圧延後に加熱処理を行った材料について、粗圧延の累積圧下率と仕上焼鈍後の鉄損との関係を示すグラフ
【図４】本発明法において、熱延仕上温度と仕上焼鈍後のリング状試料の鉄損との関係を示すグラフ
【図５】本発明法において、熱延巻取温度と仕上焼鈍後のリング状試料の鉄損との関係を示すグラフ
【図６】スラブを低温加熱し且つ粗圧延後の加熱処理を行った材料と、スラブを低温加熱し且つ粗圧延後の加熱処理を行わなかった材料について、鋼板中のＳ含有量と仕上焼鈍後および磁性焼鈍後の鉄損との関係を示すグラフ[0001]
[Technical field to which the invention belongs]
The present invention relates to a method for producing a non-oriented electrical steel sheet having low iron loss and small magnetic anisotropy.
[0002]
[Prior art]
Non-oriented electrical steel sheets are used in large quantities as iron core materials for various motors, and magnetic flux density and iron loss are emphasized as magnetic characteristics. Non-oriented electrical steel sheets are divided into full-process materials and semi-process materials. Of these, the full process material obtains predetermined magnetic properties by finish annealing on the steel manufacturer side. On the other hand, semi-processed materials are obtained by performing stress relief annealing after punching at the customer, and in this semi-processed material, crystal grains grow simultaneously with the removal of processing strain during strain relief annealing. Therefore, it is possible to further reduce the iron loss. For this reason, strain relief annealing is also called magnetic annealing.
[0003]
Conventionally, low-Si electrical steel sheets with a Si content of 1 wt% or less were often used without magnetic annealing, but in recent years, there has been a demand for lower material costs and higher efficiency and energy saving of electrical equipment. As a result, the ratio of use by upgrading due to low iron loss by magnetic annealing is increasing year by year.
[0004]
In general, when fine precipitates are present in a steel sheet, grain growth at the time of finish annealing or magnetic annealing is hindered, and it is not possible to reduce iron loss. Among such precipitates, it is known that fine MnS, AlN, and oxide particularly inhibit grain growth and significantly deteriorate iron loss in low Si magnetic steel sheets of Si: 1.5 wt% or less. . Therefore, in order to suppress the influence of such precipitates and improve the grain growth property of the steel sheet, it is effective to greatly reduce the amount of precipitates or make the precipitates harmless to make them harmless.
In order to reduce the amount of precipitates, it is necessary to reduce the amount of precipitate-forming elements such as N and S. For this purpose, desulfurization in the secondary scouring process, strengthening of denitrification, and long-term degassing treatment are required. Thus, an increase in steelmaking cost is inevitable.
[0005]
On the other hand, as a coarsening method of precipitates, a technique related to lowering the slab heating temperature has been proposed. For example, Japanese Patent Publication No. 50-35885 discloses a technique for coarsely precipitating AlN by heating a slab of Si: 3.5 wt% or less and Al: 1 wt% or less to 1200 ° C. or less. No. 42501 discloses fine precipitation of MnS during hot rolling by heating a slab of Si: 1.5 wt% or less, Al: 0.5 wt% or less, S: 0.0050 wt% or less to 1100 ° C. or less. Techniques for preventing each are disclosed.
[0006]
[Problems to be solved by the invention]
However, by simply lowering the slab heating temperature in this way, there is a limit to detoxification of fine precipitates, and sufficient magnetic properties cannot be obtained. In recent years, magnetic annealing performed by customers tends to be performed at lower temperature and shorter time, and in order to obtain a non-oriented electrical steel sheet having excellent magnetic properties, it is necessary to further detoxify fine precipitates. Become.
[0007]
In recent years, a technique related to direct feed rolling without slab heating or heat retention has been proposed. For example, JP-A-1-225726 discloses 950 after rough rolling in direct feed rolling of a slab containing Si: 1.5 wt% or less. A technique for coarsening the size of AlN by heating for 30 seconds or more in a temperature range of ° C or higher is shown. Japanese Patent Application Laid-Open No. 8-73939 discloses a technique of maintaining a surface temperature of 930 ° C. or more for 60 seconds or more after rough rolling in hot rolling of a slab to which Sb, Sn, Cu or the like is added in order to improve magnetic flux density. It is shown. In direct feed rolling, the slab is not cooled to near room temperature, so the precipitates tend to be finer. For this reason, in each of the above techniques, the precipitates are coarsened by holding for a certain time after rough rolling. Therefore, the magnetic properties of the steel sheet obtained by these techniques are only about the same level as that of a conventional general slab heating material (a material obtained by reheating a normal temperature slab and hot rolling).
[0008]
By the way, regarding magnetic steel sheets for rotating machine iron cores, conventionally, it has been emphasized that the magnetic properties in the circumferential direction are superior to the average magnetic properties in the coil longitudinal direction and the coil perpendicular direction as in the JIS-C2550 method. Yes. The circumferential characteristics are evaluated with a ring-shaped sample close to the actual excited state, and it is required that the magnetic anisotropy is small and the average magnetic characteristics in all directions on the plate surface are uniform.
[0009]
For example, Japanese Patent Application Laid-Open No. Sho 59-123715 and Japanese Patent Publication No. 6-104865 propose a method for producing a non-oriented electrical steel sheet that can obtain good magnetic properties even when measured with a ring-shaped sample. In JP-A-59-123715, the coiling temperature after hot rolling a slab having a composition of Si: 4.0 wt% or less and Al: 1.0 wt% or less is set to 700 to 950 ° C., and self-annealing is performed. A method is described in which the hot-rolled sheet has a crystal grain size of 4 or less and then cold rolling is performed at a rolling reduction of 85% or more. However, even with this technique, it is difficult to stably coarsen the crystal grains of the hot-rolled sheet, and the hot-rolled sheet has a thickness of 4 to 5 mm because it requires cold rolling under a rolling reduction of 85% or more. It is difficult to realize from the viewpoint of the mill power of the cold rolling mill.
[0010]
As described above, the magnetic properties of the non-oriented electrical steel sheets produced by the prior art are never satisfactory, and as a result, the fine precipitates can be further reduced, and good magnetic properties can be obtained even for ring-shaped samples. Therefore, it has been desired to develop a new technique capable of stably and inexpensively manufacturing a low-Si electrical steel sheet that can obtain the above-described characteristics.
Therefore, the object of the present invention is to solve such problems of the prior art, render the fine precipitates that inhibit grain growth as harmless as possible, and stabilize the non-oriented electrical steel sheet with low iron loss and small magnetic anisotropy. It is to propose a method that can be manufactured.
[0011]
[Means for Solving the Problems]
The present inventors have studied a method for producing a low-Si electromagnetic steel sheet having low iron loss and small magnetic anisotropy. As a result, in the hot rolling process of a continuous cast slab having a specific composition, (1) slab After setting the heating temperature to a specific low temperature region, (2) rough rolling the slab at a specific range of cumulative reduction, and (3) heating the rough rolled material online, More preferably, the finishing temperature and the coiling temperature at that time are optimized by adopting a series of manufacturing conditions in which the temperature is raised to a temperature higher than 20 ° C. and lower than the slab heating temperature and then finish rolling is performed. As a result, it has been found that the iron loss is effectively reduced and the magnetic anisotropy is also reduced.
[0012]
The present invention has been made based on such findings, and the features thereof are as follows.
[1] C: 0.005 wt% or less, P: 0.2 wt% or less, N: 0.0017 to 0.005 wt %, Si: 0.1 wt% or more and less than 1.5 wt%, Mn: 0.2 to 0 .5 wt%, S: 0.0050 to 0.02 wt %, Sol. Al: Continuous casting slab having a composition composed of 0.004 wt% or less or 0.1 to 0.4 wt%, the balance Fe and inevitable impurities is heated to 950 to 1150 ° C. and subjected to rough rolling with a cumulative reduction ratio of 75% or more. Subsequently, the rough rolled material is heated on-line to raise the temperature to 20 ° C. or more higher than the rough rolling finish temperature and to a temperature equal to or lower than the slab heating temperature, and then finish rolling, followed by descaling, cold rolling and A method for producing a non-oriented electrical steel sheet, characterized by annealing.
[0013]
[2] Production of non-oriented electrical steel sheet characterized in that, in the production method of [1], the hot rolling finishing temperature is [Ar ₁ transformation point +20] ° C. or higher, and the coiling temperature is 640 to 750 ° C. Method.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the details of the present invention will be described together with the reasons for limitation.
In the present invention, a continuous cast slab having a specific composition is used as a raw material, and when this is hot-rolled, the slab is heated to 950 to 1150 ° C. and subjected to rough rolling with a cumulative reduction ratio of 75% or more. The rolled material is heated online to raise the temperature to 20 ° C. or more higher than the rough rolling finish temperature and lower than the slab heating temperature, then finish rolling, and then descaling, cold rolling and annealing.
[0015]
First, in order to investigate the influence of the slab heating temperature on the iron loss, the following test was performed.
C: 0.0025 wt%, Si: 0.15 wt%, Mn: 0.40 wt%, P: 0.090 wt%, S: 0.0050 wt%, Sol. Al: 0.0012 wt%, N: 0.0025 wt%, T.I. O: Steel having a composition of 0.010 wt% was melted and cast to prepare a slab having a thickness of 220 mm. The slab was heated from room temperature to 950 to 1250 ° C. for 1 hour, then roughly rolled to a thickness of 30 mm, and then finish-rolled to a thickness of 2.3 mm without being subjected to heat treatment. Next, the hot-rolled sheet was pickled, then cold-rolled to a thickness of 0.5 mm, and further subjected to finish annealing at 750 ° C. for 1 minute.
[0016]
The iron loss of each steel plate thus obtained was measured using a 25 cm Epstein test piece, and the relationship between the slab heating temperature and the iron loss after finish annealing was examined. The result is indicated by a circle in FIG. According to the figure, it can be seen that the iron loss is reduced by lowering the slab heating temperature. This is considered to be because the re-dissolution amount of MnS during slab heating is reduced by slab heating in a low temperature region, and fine precipitation during hot rolling is suppressed, resulting in improved grain growth.
[0017]
Next, in order to investigate the relationship between the slab heating temperature and the iron loss when the heat treatment was performed after rough rolling, the following test was performed.
A slab having the same composition as that of the slab used in the above test was heated from room temperature to 950 to 1250 ° C. for 1 hour, then roughly rolled to a sheet thickness of 30 mm, and this coarsely rolled material was immediately heated to 40 ° C. above the rough rolling end temperature. After raising the temperature to a high temperature (temperature increase ΔT: 40 ° C. relative to the end temperature of rough rolling), finish rolling was performed to a plate thickness of 2.3 mm. Next, the hot-rolled sheet was pickled, then cold-rolled to a thickness of 0.5 mm, and further subjected to finish annealing at 750 ° C. for 1 minute. The temperature of the rough rolled material before the heat treatment (rough rolling end temperature) was set to 900 ° C.
The iron loss of each steel plate thus obtained was measured using a 25 cm Epstein test piece, and the relationship between the slab heating temperature and the iron loss after finish annealing was examined. The result is shown by the mark ● in FIG.
[0018]
According to FIG. 1, it can be seen that the steel sheet subjected to the heat treatment after rough rolling has a reduced iron loss as compared with the steel sheet not subjected to the heat treatment, and the effect is particularly remarkable in the steel plate having a slab heating temperature of 1150 ° C. or less. . The reason why the iron loss is remarkably lowered by performing the heat treatment after the rough rolling is not necessarily clear, but the following reasons are conceivable. That is, the strain of the precipitation nuclei of MnS dissolved in the steel is obtained by performing online heat treatment on the rough rolled material in which the processing strain is introduced by rough rolling and the energy required for precipitation of MnS is reduced. This is considered to be because induced growth occurs, and the coarsening of MnS proceeds immediately after rough rolling or before the finish rolling starting from this nucleus. In addition, since the γ particle size is increased by this heat treatment, it is considered that the particle size after finish annealing also increases. On the other hand, in a steel sheet that is not subjected to heat treatment after rough rolling, strain-induced growth of precipitation nuclei is unlikely to progress, so that MnS is finely precipitated during finish rolling, and the grain growth property is considered to be reduced.
[0019]
The reason why low iron loss by heat treatment after rough rolling is not sufficiently obtained in a steel sheet having a slab heating temperature of over 1150 ° C. is that the temperature range during rough rolling becomes high as the slab heating temperature rises, It is considered that work strain is not effectively introduced at the time of rough rolling, so that strain-induced growth of precipitation nuclei does not occur sufficiently even when heat treatment is performed after rough rolling.
For the reasons described above, in the present invention, the slab heating temperature when heating the slab from room temperature is set to 1150 ° C. or less, which is a temperature range in which the iron loss is significantly reduced by the heat treatment after rough rolling. On the other hand, if the slab heating temperature is less than 950 ° C., finish rolling becomes difficult, so the lower limit of the slab heating temperature is 950 ° C.
[0020]
Next, in order to investigate the influence of the temperature increase ΔT by the heat treatment after the rough rolling on the iron loss, the following test was performed.
C: 0.0025 wt%, Si: 0.15 wt%, Mn: 0.35 wt%, P: 0.090 wt%, S: 0.0050 wt%, Sol. Al: 0.0013 wt%, N: 0.0030 wt%, T.I. O: Steel having a composition of 0.010 wt% was melted and cast to prepare a slab having a thickness of 220 mm. The slab was heated to 1080 ° C. for 1 hour and then roughly rolled to a plate thickness of 30 mm. The temperature of this rough rolled material (rough rolling end temperature) was 905 ° C. Subsequently, this rough rolled material was heated by a solenoid induction heating device to raise the temperature to 910 ° C. to 1055 ° C. (temperature increase amount relative to the rough rolling end temperature: 5 to 150 ° C.), and then finish rolling was performed. Next, the hot-rolled sheet was pickled, then cold-rolled to a thickness of 0.5 mm, and further subjected to finish annealing at 750 ° C. for 1 minute.
[0021]
The iron loss of each steel plate thus obtained was measured using a 25 cm Epstein test piece, and the temperature increase ΔT (temperature increase relative to the end temperature of the rough rolling, the same applies hereinafter) and finish annealing by heat treatment after rough rolling. The relationship with iron loss later was investigated. The result is shown in FIG. According to the figure, the effect of reducing iron loss increases when the temperature increase ΔT by heat treatment after rough rolling is 20 ° C. or higher.
For the above reasons, in the present invention, subsequent to the rough rolling, the rough rolled material is heated to a temperature that is 20 ° C. higher than the end temperature of the rough rolling, and then finish rolling is performed. However, if the heating temperature after the rough rolling exceeds the slab heating temperature, the remelting of the precipitate proceeds and the grain growth property decreases, so the heating temperature after the rough rolling is set to be equal to or lower than the slab heating temperature.
[0022]
Next, in order to investigate the influence of the cumulative rolling reduction ratio of the rough rolling on the iron loss, the following test was performed.
C: 0.0025 wt%, Si: 0.15 wt%, Mn: 0.35 wt%, P: 0.100 wt%, S: 0.0060 wt%, Sol. Al: 0.0012 wt%, N: 0.0030 wt%, T.I. O: Steel having a composition of 0.010 wt% was melted and cast to prepare slabs having a thickness of 300 mm, 250 mm, 220 mm, 150 mm, 120 mm, 100 mm, and 80 mm. These slabs were heated to 1100 ° C. for 1 hour and then roughly rolled to a plate thickness of 30 mm. The temperature of this rough rolled material was 890 ° C. Subsequently, this rough rolled material was heated by a solenoid induction heating device to raise the temperature to 930 ° C. (temperature increase amount relative to the rough rolling end temperature: 40 ° C.), and then finish rolling was performed. Next, the hot-rolled sheet was pickled, then cold-rolled to a thickness of 0.5 mm, and further subjected to finish annealing at 750 ° C. for 1 minute.
[0023]
The iron loss of each steel plate thus obtained was measured using a 25 cm Epstein test piece, and the relationship between the cumulative rolling reduction ratio of rough rolling and the iron loss after finish annealing was examined. The result is shown in FIG. According to the figure, it can be seen that the iron loss is effectively reduced by setting the cumulative rolling reduction in rough rolling to 75% or more. On the other hand, if the cumulative rolling reduction in rough rolling is less than 75%, the introduction of strain energy for reducing the driving force required for precipitation of MnS is insufficient, so that MnS is less likely to be coarsened. The loss is high.
Therefore, in the present invention, the lower limit of the cumulative rolling reduction of rough rolling is set to 75%. The upper limit of the cumulative rolling reduction is not particularly specified because it is determined by the mill power of the roughing mill.
[0024]
Next, as a result of examining the influence of the hot rolling finishing temperature and the coiling temperature, the slab was heated to 950 to 1150 ° C. and subjected to rough rolling with a cumulative reduction ratio of 75% or more, and subsequently 20 ° C. or higher than the rough rolling finish temperature. It has been found that the magnetic anisotropy can be further reduced by optimizing the hot rolling finishing temperature and the coiling temperature for the rough rolled material heated to a high temperature and lower than the slab heating temperature.
[0025]
First, in order to investigate the influence of hot rolling finishing temperature on magnetic anisotropy, the following tests were conducted.
C: 0.0025 wt%, Si: 0.15 wt%, Mn: 0.40 wt%, P: 0.090 wt%, S: 0.0060 wt%, Sol. Al: 0.0012 wt%, N: 0.0025 wt%, T.I. O: Steel having a composition of 0.010 wt% was melted and cast to prepare a slab having a thickness of 220 mm. The slab was heated to 1100 ° C. for 1 hour, and then roughly rolled to a plate thickness of 30 mm. Subsequently, the rough rolled material was heated by a solenoid induction heating device to 940 ° C. (temperature increase ΔT: 40 ° C. relative to the end temperature of the rough rolling) ) And then finish rolling to a plate thickness of 2.3 mm. At this time, the finishing temperature was 920 to 780 ° C., and the winding temperature was 670 ° C. Next, the hot-rolled sheet was pickled, then cold-rolled to a thickness of 0.5 mm, and further subjected to finish annealing at 750 ° C. for 1 minute. Incidentally, the measured transformation point of the steel used, Ar ₃ transformation point: 870 ° C., Ar ₁ transformation point: was 810 ° C..
[0026]
A ring test piece having an outer diameter of 45 mm and an inner diameter of 33 mm was cut out from each steel sheet coil, and five of these were laminated to evaluate the magnetic properties, and the relationship between the hot rolling finishing temperature and the iron loss of the ring-shaped sample was examined. The result is shown in FIG.
According to FIG. 4, when the hot rolling finishing temperature is [Ar ₁ transformation point +20] ° C. or higher, the iron loss measured with the ring-shaped sample is lowered, and when the hot rolling finishing temperature is higher than Ar ₃ transformation point, there is a tendency to further decrease. This is considered to be because the texture is randomized by terminating the hot rolling at the above temperature or more, thereby reducing the magnetic anisotropy.
Therefore, in the present invention, the hot rolling finishing temperature is preferably [Ar ₁ transformation point +20] ° C. or higher, preferably Ar ₃ transformation point or higher.
[0027]
Next, in order to investigate the influence of the hot rolling coiling temperature on the magnetic anisotropy, the following tests were conducted.
A slab having the same composition as the slab used in the above test was roughly rolled and subjected to heat treatment after rough pressing under the same conditions. Subsequently, this rough rolled material was finish-rolled at a finishing temperature of 840 ° C. to a sheet thickness of 2.3 mm, and then wound. It wound up at the temperature of 600-750 degreeC. Next, after pickling the hot-rolled sheet, it was cold-rolled to a sheet thickness of 0.5 mm and further subjected to finish annealing at 750 ° C. × 1 minute.
A ring test piece having an outer diameter of 45 mm and an inner diameter of 33 mm was cut out from each steel sheet coil, and five of these were laminated to evaluate magnetic properties, and the relationship between the hot rolling coiling temperature and the iron loss of the ring-shaped sample was examined. The result is shown in FIG.
[0028]
According to FIG. 5, when the coiling temperature is less than 640 ° C., the iron loss of the ring-shaped sample is high. In addition, when the coiling temperature is less than 640 ° C., the ferrite grain size of the hot-rolled sheet is also reduced, which causes a decrease in magnetic flux density.
Therefore, in the present invention, the winding temperature is preferably 640 ° C. or higher. However, if the coiling temperature is excessively high, the pickling temperature is limited to 750 ° C., because the pickling property decreases due to the increase in the scale thickness of the hot-rolled sheet and the characteristics vary within the coil. preferable.
[0029]
Next, the reason for limiting the steel composition in the present invention will be described.
Since C causes magnetic aging and deteriorates magnetic properties, it is set to 0.005 wt% or less .
P has the effect of increasing the hardness of the steel sheet and improving the punching workability. However, excessive addition causes deterioration of the cold rolling property, so it is 0.2 wt% or less .
Si is an element that reduces iron loss as the amount of addition increases. To reduce iron loss, it is necessary to add 0.1 wt% or more, but when it exceeds 1.5 wt%, the magnetic flux density decreases. For this reason, Si amount shall be 0.1 wt% or more and less than 1.5 wt%.
[0030]
As the amount of Mn increases, the amount of MnS redissolved during slab heating decreases, and the amount of MnS finely precipitated during hot rolling decreases, so that the grain growth property is improved. This tendency is remarkable until the amount of Mn is about 0.5 wt%, and the electrical resistance is increased, which is advantageous for reducing the iron loss. However, excessive addition of Mn exceeding 0.5 wt% causes an increase in cost. On the other hand, if the amount of Mn is less than 0.2 wt%, the amount of MnS that is re-dissolved during slab heating increases, and MnS that finely precipitates during hot rolling increases. For this reason, even if it heat-processes after rough rolling, it will become impossible to ensure the grain growth property especially after magnetic annealing. For this reason, the amount of Mn shall be 0.2-0.5 wt%.
[0031]
S binds to Mn and precipitates finely as MnS and inhibits grain growth, so it is desirable to reduce it as much as possible. However, in the present invention, this MnS can be made harmless to some extent, so the amount of S is limited to 0.02 wt%. Therefore, the S amount is 0.02 wt% or less .
Although the present invention allows the S content in the above range, the present invention functions more effectively in such a range, particularly in the region where the S content is high. In order to investigate the relationship between the S content of the steel sheet and the effect of the present invention, the following test was performed.
[0032]
C: 0.003 wt%, Si: 0.16 wt%, Mn: 0.35 wt%, P: 0.090 wt%, P: 0.100 wt%, S: 0.0050 to 0.0220 wt%, Sol. A steel having a composition of Al: 0.0012 wt% and N: 0.0030 wt% was melted and cast to prepare a slab having a thickness of 220 mm. The slab was heated to 1100 ° C. for 1 hour and then roughly rolled to a thickness of 30 mm. Subsequently, the rough rolled material was heated by a solenoid induction heating device to raise the temperature to 40 ° C. higher than the rough rolling end temperature, and then finish rolling was performed. Further, the slab having the same composition and size as described above was subjected to rough rolling and finish rolling under exactly the same conditions as described above except that heat treatment after rough rolling was not performed. Next, after pickling these hot-rolled sheets, they were cold-rolled to a thickness of 0.5 mm, subjected to finish annealing at 750 ° C. × 1 minute, and further subjected to magnetic annealing at 750 ° C. × 2 hours.
[0033]
FIG. 6 shows the relationship between the S content of the steel sheet thus obtained and the iron loss after finish annealing and after magnetic annealing. According to the figure , the iron loss increases with the increase of S content, but the increase in iron loss is significantly suppressed in the steel plate that was heat-treated after rough rolling compared to the steel plate that was not heat-treated. In addition, the effect of reducing the iron loss is particularly great when the S content is high. However, when the S content exceeds 0.02 wt%, not only the iron loss itself increases, but also the effect of reducing the iron loss by heat treatment becomes small.
If the content of N is large, the amount of precipitation of nitride increases, the grain growth property during magnetic annealing decreases, and the iron loss increases. For this reason, N amount shall be 0.005 wt% or less .
[0034]
Sol. Al significantly inhibit grain growth because of combining with N to form fine AlN in the range of trace addition of less than 0.004 wt% ultra ～0.1Wt%, Ru deteriorate the magnetic properties. On the other hand, Sol. When Al is added in an amount of 0.1 wt% or more, AlN becomes coarse and the magnetic characteristics are not deteriorated, and Al contributes to an increase in specific resistance. However, if it exceeds 0.4 wt%, the magnetic flux density is lowered. For this reason, Sol. Al is 0.004 wt% or less or 0.1 to 0.4 wt%.
As other elements, 0.05 wt% or less of Sb and 0.05 wt% or less of Sn can be added for the purpose of improving magnetic properties.
The balance is substantially made of Fe and does not prevent inclusion of a small amount of component elements such as inevitable impurity elements.
[0035]
In the manufacturing method of the present invention, there are no special restrictions other than the manufacturing conditions described above, and therefore normal manufacturing conditions may be adopted. That is, after the molten steel blown in the converter is degassed and adjusted to a predetermined component, it is cast into a slab, and this slab is hot-rolled under the conditions described above. Moreover, although hot-rolled sheet annealing after hot rolling may be performed, it is not essential. Next, after a predetermined sheet thickness is obtained by two or more cold rollings with one cold rolling or intermediate annealing, finish annealing is performed, and magnetic annealing is further performed as necessary.
[0036]
【Example】
[Example 1]
Steel having the composition shown in Table 1 was melted through converter blowing and degassing treatment, and a slab having a thickness of 230 mm was formed by continuous casting. These slabs were hot-rolled under the conditions shown in Table 2 to a plate thickness of 2.3 mm. At this time, the rough rolling end temperature was 900 ° C., the finishing temperature was 820 to 850 ° C., and the winding temperature was 650 to 680 ° C. Next, the hot-rolled coil was pickled and cold-rolled to a thickness of 0.5 mm, and then subjected to finish annealing (each annealing temperature × 1 minute) under the conditions shown in Table 2, and then 750 ° C. × 2 hours. Magnetic annealing was performed.
The magnetic properties of each steel sheet after finish annealing and after magnetic annealing were measured using 25 cm Epstein test pieces. The results are also shown in Table 2.
According to Table 2, it can be seen that in the present invention example, a non-oriented electrical steel sheet having low iron loss after finish annealing and after magnetic annealing is obtained.
[0037]
[Table 1]

[0038]
[Table 2]

[0039]
[Example 2]
Steel No. 1 (Ar ₁ transformation point: 810 ° C.) and Steel No. 4 (Ar ₁ transformation point: 840 ° C.) shown in Table 1 were melted to form a slab having a thickness of 230 mm by continuous casting. These slabs were heated to 1100 ° C., then roughly rolled to a plate thickness of 32 mm, and subsequently heated by a solenoid type induction heating device to raise the temperature to 35 ° C. higher than the end temperature of rough rolling, and then shown in Table 3. Finish rolling was performed under the conditions to obtain a hot-rolled sheet having a sheet thickness of 2.3 mm. Next, after pickling the hot-rolled coil, it was cold-rolled to a thickness of 0.5 mm, subjected to finish annealing at 750 ° C. × 1 minute, and further subjected to magnetic annealing at 750 ° C. × 2 hours.
[0040]
The magnetic properties of each steel plate obtained after finish annealing and after magnetic annealing were measured using a ring test piece having an outer diameter of 45 mm and an inner diameter of 33 mm. The results are also shown in Table 3.
According to Table 3, in the manufacturing method of the present invention, the iron loss of the ring-shaped sample after finishing annealing and after magnetic annealing is low by controlling the hot rolling finishing temperature and the coiling temperature within specific ranges. It can be seen that an electrical steel sheet is obtained.
[0041]
[Table 3]

[0042]
【The invention's effect】
As described above, according to the present invention, a non-oriented magnetostatic steel sheet having low iron loss and small magnetic anisotropy can be stably produced.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between slab heating temperature and iron loss after finish annealing for a material that has been heat-treated after rough rolling and a material that has not been heat-treated. FIG. FIG. 3 is a graph showing the relationship between the temperature rise ΔT by heat treatment after rough rolling and the iron loss after finish annealing. FIG. 3 shows the cumulative reduction of rough rolling for materials that are heated at low temperature and subjected to heat treatment after rough rolling. FIG. 4 is a graph showing the relationship between the hot rolling finishing temperature and the iron loss of a ring-shaped sample after finish annealing in the method of the present invention. Graph showing the relationship between the hot rolling coiling temperature and the iron loss of the ring-shaped sample after finish annealing in the method. [Fig. 6] A material in which the slab is heated at low temperature and subjected to heat treatment after rough rolling, and the slab at low temperature Heated material that was not heat-treated after rough rolling For it, a graph showing the relationship between the S content and final annealing and after iron loss after the magnetic annealing in the steel sheet

Claims

C: 0.005 wt% or less, P: 0.2 wt% or less, N: 0.0017 to 0.005 wt %, Si: 0.1 wt% or more and less than 1.5 wt%, Mn: 0.2 to 0.5 wt% , S: 0.0050 to 0.02 wt %, Sol. Al: Continuous casting slab having a composition composed of 0.004 wt% or less or 0.1 to 0.4 wt%, the balance Fe and inevitable impurities is heated to 950 to 1150 ° C. and subjected to rough rolling with a cumulative reduction ratio of 75% or more. Subsequently, the rough rolled material is heated on-line to raise the temperature to 20 ° C. or more higher than the rough rolling finish temperature and to a temperature equal to or lower than the slab heating temperature, and then finish rolling, followed by descaling, cold rolling and A method for producing a non-oriented electrical steel sheet, characterized by annealing.

The method for producing a non-oriented electrical steel sheet according to claim 1, wherein the hot rolling finishing temperature is set to [Ar ₁ transformation point +20] ° C. or more, and the coiling temperature is set to 640 to 750 ° C.