JP4196568B2 - Method for producing grain-oriented electrical steel sheet - Google Patents

Description

ここで、σは変形抵抗、εは歪、
【外１】

は歪速度、Ｔは温度、ＣとＡは定数である。
この式を温度で微分すると、
【数２】

となる。
すなわち、長手方向の変形抵抗の変化は、同じ温度変化なら、低温の方が大きくなる。従って、長手方向の温度勾配による変形抵抗の変化が、スラブ低温加熱ではより大きいものなり、耳割れが頻繁に発生するようになったものと考えられる。
【００３２】
また、長手方向の温度勾配は、あまり圧下されていない、つまり長手方向に伸ばされていない場合の方が大きいので、粗圧延時の方が変形抵抗の勾配は大きい。従って、粗圧延中に、板厚が厚いために耳割れとならなくとも、耳割れの起点となる亀裂は生じていると考えられる。このことも、粗圧延が低温となるスラブ低温加熱において耳割れが発生し易くなった一因と考えられる。
【００３３】
一方、仕上圧延の後段では、さらに圧延温度が低くなるが、十分に長手方向に伸ばされ、スキッド間隔に対応する長さも十分に長くなるため、長手方向の温度勾配は小さくなり、上述の機構による耳割れが発生し難くなると考えられる。
従って、本発明のように低温でスラブ加熱を行う場合、耳割れが最も発生し易い段階は、熱延の途中である仕上圧延の前段であり、この段階でエッジ部長手方向、特にスキッド対応位置近傍での温度勾配を緩やかにすることにより、耳割れの発生が抑制されたものと考えられる。
【００３４】
なお、本発明のように、インヒビターを含有しない場合、たとえスラブを低温で加熱したとしても、スラブ加熱後に結晶の成長は抑制されずに粒径が粗大化してしまう。これが、前述した機構による耳割れの発生をさらに助長し、耳割れの発生が増加したものと考えられる。
以上から、耳割れを低減するためには、シートバーにおける長手方向の温度勾配を小さくすることが重要である。
本発明は、上記した知見に基づき、さらに検討を加えて完成されたものである。
【００３５】
すなわち、本発明の要旨構成は次のとおりである。
１．質量％で、Ｃ：0.080％以下, Si：2.0〜8.0 ％及びMn：0.005〜3.0 ％を含み、Alを 100 ppm未満、Ｎ, Ｓ, Seをそれぞれ 50ppm以下に低減した組成になる鋼スラブを、1250℃未満の温度に加熱したのち、熱間圧延し、必要に応じて熱延板焼鈍を行ったのち、１回または中間焼鈍を挟む２回以上の冷間圧延を行い、ついで脱炭焼鈍後、必要に応じて焼鈍分離剤を塗布してから、最終仕上焼鈍を施す一連の工程によって方向性電磁鋼板を製造するに際し、
上記スラブ加熱工程におけるそれぞれのスキッド間隔をＤ_i （ｍ）、粗圧延出側でのスキッド間隔内における温度差をΔＴ_i （℃）、熱間粗圧延の圧下率をＲ（％）とする時、上記Ｄ _i 、ΔＴ _i およびＲを相互に調整することにより、次式(1)
Ｔ_i ′＝ΔＴ_i ×（１−Ｒ÷100 ）÷Ｄ_i --- (1)
により計算した粗圧延直後のＴ_i′の内の最大値Ｔ′を10.0℃/m以下に制御することを特徴とする、方向性電磁鋼板の製造方法。
【００３６】
２．上記１において、鋼スラブが、質量％でさらに、Ni：0.005 〜1.50％、Sn：0.01〜0.50％、Sb：0.005 〜0.50％、Cu：0.01〜1.50％、Ｐ：0.005 〜0.50％およびCr：0.01〜1.50％のうちから選んだ１種または２種以上を含有する組成になることを特徴とする方向性電磁鋼板の製造方法。
【００３７】
【発明の実施の形態】
以下、本発明を具体的に説明する。
まず、本発明において、素材であるスラブの成分組成を上記の範囲に限定した理由について説明する。なお、成分に関する「％」表示は特に断らない限り質量％（mass％）を意味する。
Ｃ：0.080 ％以下
Ｃ量が 0.080％を超えると、磁気時効の起こらない 50ppm以下まで低減することが困難になるので、Ｃは 0.080％以下に制限した。
Si：2.0 〜8.0 ％
Siは、鋼の比抵抗を高めて鉄損を低減する有効成分であるが、含有量が 8.0％を超えると冷延性が損なわれ、一方 2.0％に満たないと高い比抵抗が得られず、十分な鉄損低減効果が得られないので、Si量は 2.0〜8.0 ％の範囲に限定した。Mn：0.005 〜3.0 ％
Mnは、熱間加工性を改善するために有用な元素であるが、含有量が 0.005％未満ではその添加効果に乏しく、一方 3.0％を超えると磁束密度の低下を招くので、Mn量は 0.005〜3.0 ％の範囲とする。
【００３８】
Al：100 ppm 未満、Ｎ, Ｓ, Seはそれぞれ 50ppm以下
また、不純物元素であるAlは 100 ppm未満、Ｎ, Ｓ, Seについても 50ppm以下、好ましくは 30ppm以下に低減することが、良好に二次再結晶させる上で不可欠である。その他、窒化物形成元素であるTi, Nb, Ｂ, Ta, Ｖ等についても、それぞれ 50ppm以下に低減することが鉄損の劣化を防止し、良好な加工性を確保する上で有効である。
【００３９】
以上、必須成分および抑制成分について説明したが、本発明では、その他にも以下に述べる元素を適宜含有させることができる。
Ni：0.005 〜1.50％、Sn：0.01〜0.50％、Sb：0.005 〜0.50％、Cu：0.01〜1.50％、Ｐ：0.005 〜0.50％、Cr：0.01〜1.50％のうちから選んだ少なくとも１種
Niは、熱延板組織を改善して磁気特性を向上させる有用元素である。しかしながら、含有量が 0.005％未満では磁気特性の向上量が小さく、一方1.50％を超えると二次再結晶が不安定になり磁気特性が劣化するので、Ni量は 0.005〜1.50％とした。
また、Sn，Sb，Cu, Ｐ, Crはそれぞれ、鉄損の向上に有用な元素であるが、いずれも上記範囲の下限値に満たないと鉄損の向上効果が小さく、一方上限量を超えると二次再結晶粒の発達が阻害されるので、それぞれSn：0.01〜0.50％，Sb：0.005 〜0.50％，Cu：0.01〜1.50％，Ｐ：0.005 〜0.50％，Cr：0.01〜1.5 ％の範囲で含有させる。
【００４０】
次に、本発明の製造工程について説明する。
上記の好適成分組成に調整した溶鋼を、転炉、電気炉などを用いる公知の方法で精錬し、必要があれば真空処理などを施したのち、通常の造塊法や連続鋳造法を用いてスラブを製造する。また、直接鋳造法を用いて 100mm以下の厚さの薄鋳片を直接製造してもよい。
【００４１】
スラブは通常の方法で加熱したのち、熱間圧延に供する。
この際、スラブ加熱温度は1250℃未満とすることが重要である。というのは、結晶組織の微細化および不可避的に混入するインヒビター成分の弊害を無害化して、均一な粒径の一次再結晶組織を実現するためには、スラブ加熱温度の低温化が必要だからである。また、熱間圧延前のスラブ加熱温度を1250℃未満に抑えることにより、熱延時に生成するスケール量を低減することもできる。
【００４２】
スラブ加熱は、ガス燃焼炉または電気式加熱炉あるいはその両方を用いてよい。加熱炉で加熱したスラブは、熱間粗圧延を行い、引き続き熱間仕上圧延を行って熱延板とする。
この時、熱延による耳割れを防止するには、シートバーの長手方向の温度勾配を小さくすることが重要である。この温度勾配は、主に加熱炉におけるスキッドが原因となる。
【００４３】
従って、熱延時における耳割れを防止するには、シートバーの温度勾配を規制するべきであるが、実際のシートバーの長手方向の測温は放射温度計等により行われ、そのため表面のスケール等の影響を受けて、スキッド間隔に対応した長さよりもかなり小さい周期で測温データは変動してしまう。このため、正確な温度勾配を求めるのは事実上不可能である。
【００４４】
そこで、本発明では、次に述べるように規制することとした。下述の方法により、シートバーの温度は、放射温度計による測温値で十分に把握することができ、下述の方法は本発明の特徴でもある。
ここで、スキッドとは、スラブの加熱に用いた最後の加熱炉におけるスラブ抽出直前に５分以上スラブに直接接し、スラブを支えていたものを指す。すなわち、スラブ抽出のために用いる移動式ビーム等はスキッドとはみなさない。また、スラブとスキッドの接触面積が大きい場合は、その中心をスキッドの位置とする。
【００４５】
まず、スラブの圧延方向先端からのスキッドの位置を、それぞれＡ₁ Ａ₂ ---Ａ_n とする（ｎはスキッドの本数）。また、Ａ₀ ＝０，Ａ_n+1 ＝スラブ長さ、とする。
それぞれのｉ番目のスキッドの間隔は、Ｄ_i ＝（Ａ_i+1 −Ａ_i-1)÷２とする（ｉ＝１，２，--- ｎ）。
また、シートバーに対応するスキッドの位置として、ａ_i ＝α×Ａ_i （ｉ＝１，２，--- ｎ）とする。
ここで、αは（シートバーの長さ÷スラブの長さ）である。
粗圧延の圧下率、すなわち100 ×（スラブの厚さ−シートバーの厚さ）÷スラブの厚さをＲとすれば、αは粗圧延中における幅圧下により多少ずれるものの、（１÷（１−Ｒ÷100)) にほぼ等しくなる。
ｉ番目のスキッド（i ＝１，２，--- ｎ）における温度差ΔＴ_i をａ_i −（ａ_i −ａ_i-1 ）×３÷４と、ａ_i ＋（ａ_i+1 −ａ_i ）×３÷４の区間におけるシートバーの温度の最大値と最小値の差とする。
上記の関係を図１に図解する。
【００４６】
さて、ｎ本のスキッドに対して、次式(1)
Ｔ_i ′＝ΔＴ_i ×（１−Ｒ÷100 ）÷Ｄ_i --- (1)
を計算し、その中の最大値をＴ′とする。
そして、耳割れを防止するためには、温度勾配の指標であるＴ_i ′の最大値Ｔ′について、次式の関係を満足するように制御する。
Ｔ′≦10.0（℃／m ）
【００４７】
上記の条件を満たすためには、加熱炉のスキッド間隔を変更する、加熱炉のスキッド部とその間の温度差を小さくする、粗圧延の圧下率を大きくする等の方法がある。
シートバーの温度は、粗圧延中の温度勾配も耳割れに影響を与えられていると考えられるので、粗圧延直後の温度とする。また、シートバーの測温位置は、幅方向最端部から100mm の間のどこでも良いが、長手方向各々の測温位置について、幅方向最端部から測温位置までの距離は同一とする。また、測温方法は、放射温度計でよく、特に規定はしない。重要なのは、長手方向における温度差ΔＴである。
このような方法で製造された熱延板では、耳割れの発生による切り捨て量が少なく製品歩留りが顕著に向上する。
【００４８】
ついで、必要に応じて熱延板焼鈍を施す。ゴス組織を製品板において高度に発達させるためには、熱延板焼鈍温度は 800〜1100℃の範囲が好適である。というのは、熱延板焼鈍温度が 800℃未満では熱延でのバンド組織が残留し、整粒の一次再結晶組織を実現することが困難になる結果、二次再結晶の発達が阻害され、一方熱延板焼鈍温度が1100℃を超えると、不可避的に混入するインヒビター成分が固溶し冷却時に不均一に再析出するために、整粒一次再結晶組繊を実現することが困難となり、やはり二次再結晶の発達が阻害されるからである。また、熱延板焼鈍温度が1100℃を超えると、熱延板焼鈍後の粒径が粗大化しすぎることも、整粒の一次再結晶組織を実現する上で極めて不利である。
【００４９】
熱延板焼鈍後、１回または中間焼鈍を挟む２回以上の冷間圧延を施したのち、脱炭焼鈍を施して、Ｃを磁気時効の起こらない 50ppm以下好ましくは 30ppm以下まで低減する。
なお、上記の冷間圧延において、圧延温度を 100〜250 ℃に上昇させて圧延を行うことや、冷間圧延の途中で 100〜250 ℃の範囲での時効処理を１回または複数回行うことが、ゴス組織を発達させる上で有効である。
【００５０】
最終冷延後の脱炭焼鈍は、湿潤雰囲気を使用して 700〜1000℃の温度で行うことが好適である。また、脱炭焼鈍後に浸珪法によってにSi量を増加させる技術を併用してもよい。
その後、必要に応じて焼鈍分離剤を適用して、最終仕上焼鈍を施すことにより二次再結晶組織を発達させる。最終仕上げ焼鈍は、二次再結晶発現のために 800℃以上で行う必要があるが、800 ℃までの加熱速度は磁気特性に大きな影響を与えないので任意の条件でよい。
【００５１】
その後、平坦化焼鈍を施して形状を矯正する。
ついで、上記の平坦化焼鈍後、鉄損の改善を目的として、鋼板表面に張力を付与する絶縁コーティングを施すことが有利である。
さらに、公知の磁区細分化技術を適用できることはいうまでもない。
【００５２】
【実施例】
実施例１
表１に鋼記号Ａ，Ｂ，Ｃで示す組成になる溶鋼からそれぞれ、厚さ：180 mm，210 mm，240 mmのスラブを連続鋳造により製造した。ついで、これらスラブを、ガス燃焼炉で1200℃に加熱したのち、粗圧延でシートバーとし、引き続き仕上圧延により2.4 mm厚の熱延板とした。
その際、加熱炉のスキッド間隔、粗圧延圧下率等は、表２に示すとおりとした。なお、No.1〜９はスキッド間隔およびスラブ厚さを変更することにより、 No.10〜12はシートバー厚さを変更することにより、 No.13〜15は温度差ΔＴを変更することにより、それぞれＴ′を変化させた。また、シートバーの温度は、幅端部から20mmの位置で長手方向に測温した。
得られた熱延板の耳割れ最大深さについて調べた結果を、表２に併記する。
【００５３】
【表１】

【００５４】
【表２】

【００５５】
表２から明らかなように、Ｔ′を10℃／m 以下とした発明例はいずれも、耳割れ最大深さが５mm以下と耳割れの発生が格段に軽減されている。
これに対し、Ｔ′が10.0℃／m を超える比較例はいずれも、最大深さが10mmを超える耳割れの発生を余儀なくされた。
【００５６】
実施例２
表１に鋼記号Ａ〜Ｖで示す組成になる溶鋼からそれぞれ、厚さ：220 mmのスラブを連続鋳造により製造した。ついで、これらスラブを、ガス燃焼炉で1180℃に加熱したのち、粗圧延により厚さ：40mmのシートバーとし、引き続き仕上圧延により厚さ：2.3 mmの熱延板とし、コイル状に巻き取った。
また、鋼記号Ｄのスラブについて、ガス燃焼炉で1180℃に加熱したのち、さらに誘導加熱炉で1350℃に加熱し、その後同様の熱延を行って比較例とした。
なお、この時の全てのスラブ熱延において、Ｔ′は10.0℃／m 以下とした。
その結果、耳割れ最大深さは全ての熱延板において５mm以下であった。
【００５７】
次に、これらの全ての熱延板に1000℃、30秒間の熱延板焼鈍を施し、35℃/sの速度で急冷後、酸洗し、ついで 240℃の温間圧延で0.34mm厚に仕上げた。
その後、脱脂処理を施したのち、H₂：50 vol％、N₂：50 vol％、露点：57℃の雰囲気中にて、 840℃, ２分間の脱炭焼鈍を施した。
ついで、MgＯにTiO₂を５mass％添加した焼鈍分離剤を、鋼板の両面に、片面当たり８g/m²塗布してから、最終仕上焼鈍として、N₂ガス中にて 850℃に48時間保持したのち、 900℃まで５℃/hの速度で昇温し、その後雰囲気ガスをN₂ガスからH₂ガスに変更して25℃/hの速度で1120℃まで昇温し、さらに雰囲気ガスをH₂ガスからN₂：25 vol％、H₂：75 vol％の混合ガスに変更して25℃/hの速度で1190℃まで昇温し、ついでH₂ガスに変更したのち1190℃で８時間保持後、 600℃までH₂ガス中で降温し、 600℃からはArガス中で降温する、処理を行った。
上記の最終仕上焼鈍後、未反応の焼鈍分離剤を除去してから、50％のコロイダルシリカを含有するリン酸マグネシウムを張力コーティングとして塗布した後、840 ℃で30秒間焼き付けて製品板とした。
かくして得られた製品板について、磁束密度Ｂ₈ および鉄損Ｗ_17/50 を測定すると共に、被膜密着性を評価した。なお、被膜密着性は、曲げ剥離径（鋼板を丸棒に巻きつけて被膜が剥離しない最小の曲げ径）にて評価した。その結果を表３に示す。
【００５８】
【表３】

【００５９】
同表に示したとおり、インヒビター元素を本発明の上限を超えて含有する鋼記号Ｑ〜Ｖおよび1350℃にスラブ加熱した記号Ｄはいずれも、磁気特性が劣化していた。
これに対し、成分組成およびスラブ加熱温度が本発明の適正範囲を満足する鋼記号Ａ〜Ｐはいずれも、磁気特性および被膜特性とも良好であった。
【００６０】
【発明の効果】
かくして、本発明によれば、方向性電磁鋼板の製造に際し、スラブ加熱温度を1250℃未満に抑制した場合に熱間圧延工程で懸念された耳割れの発生を効果的に軽減することができ、ひいてはかかる耳割れに起因した端部切り捨て量を格段に低減して、製品歩留りを飛躍的に向上させることができ、産業上極めて有用である。
【図面の簡単な説明】
【図１】 方向性電磁鋼板の一次再結晶組織における方位差角が20〜45°である粒界の各方位粒に対する存在頻度（％）を示した図である。
【図２】 温度差ΔＴ_i の算出要領説明図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing a grain-oriented electrical steel sheet mainly used for iron core materials such as power transformers, and particularly aims to advantageously reduce ear cracks during hot rolling.
[0002]
[Prior art]
Oriented electrical steel sheets are mainly used as iron cores for transformers and other electrical equipment, and are basically required to be excellent in magnetic properties such as magnetic flux density and iron loss in order to adapt to such applications. Therefore, what is important in the manufacture of grain-oriented electrical steel sheets is to highly accumulate the orientation of crystal grains to be recrystallized in the so-called finish annealing process in the {110} <001> orientation, so-called Goth orientation. .
As a general technique for effectively promoting the accumulation of such secondary recrystallization, there is a method using a precipitate called an inhibitor.
[0003]
For example, Japanese Patent Publication No. 40-15644 discloses a method using AlN, MnS as an inhibitor, and Japanese Patent Publication No. 51-13469 discloses a method using MnS, MnSe as an inhibitor. Has been put to practical use.
Apart from these, a technique for adding CuSe and BN is disclosed in Japanese Patent Publication No. 58-42244, and a method using a nitride of Ti, Zr, V, etc. is disclosed in Japanese Patent Publication No. 46-40855.
[0004]
The method using these inhibitors is a useful method for stably developing secondary recrystallized grains, but the precipitate must be finely dispersed, so the slab heating before hot rolling is 1300 ° C or higher. It is necessary to carry out at a high temperature.
However, high-temperature heating of the slab has problems such as an increase in equipment cost and an increase in the amount of scale generated during hot rolling, resulting in a decrease in yield and complicated maintenance of the equipment.
[0005]
On the other hand, methods for producing grain-oriented electrical steel sheets without using an inhibitor are disclosed in JP-A 64-55339, JP-A-2-57635, JP-A-7-76732 and JP-A-7-197126. Is disclosed. What is common to these techniques is that the {110} plane is intended to grow preferentially using surface energy as the driving force.
In order to effectively use the surface energy, it is necessary to reduce the plate thickness in order to increase the contribution of the surface. For example, in the technique disclosed in Japanese Patent Laid-Open No. 64-55339, the thickness is limited to 0.2 mm or less, and in the technique disclosed in Japanese Patent Laid-Open No. 2-57635, the thickness is limited to 0.15 mm or less.
However, since the thickness of the grain-oriented electrical steel sheet that is currently used is almost 0.20 mm or more, it is difficult to produce a normal grain-oriented electrical steel sheet by the method using the surface energy as described above.
[0006]
Furthermore, in order to utilize the surface energy, it is necessary to perform high-temperature final finish annealing in a state in which the generation of surface oxides is suppressed. For example, in the technique disclosed in Japanese Patent Laid-Open No. 64-55339, a vacuum or an inert gas, or a hydrogen gas or a mixed gas of hydrogen gas and nitrogen gas is used as an atmosphere for final finish annealing at a temperature of 1180 ° C. or higher. It is required to be used.
In the technique disclosed in JP-A-2-57635, an inert gas atmosphere or hydrogen gas or a mixed atmosphere of hydrogen gas and inert gas is used at a temperature of 950 to 1100 ° C., and the pressure is reduced. Is recommended.
Furthermore, the technique disclosed in Japanese Patent Application Laid-Open No. 7-197126 describes that the final finish annealing is performed in a non-oxidizing atmosphere or a vacuum at a temperature of 1000 to 1300 ° C. and an oxygen partial pressure of 0.5 Pa or less. .
[0007]
Thus, when trying to obtain good magnetic properties using surface energy, the atmosphere of the final finish annealing requires an inert gas or hydrogen gas, and it is required to be a vacuum as a recommended condition. However, coexistence of high temperature and vacuum is extremely difficult in terms of equipment, and the cost is high.
[0008]
Furthermore, when surface energy is used, in principle, only the {110} plane can be selected, and the growth of goth grains with the <001> direction aligned in the rolling direction is not selected. Absent.
The grain-oriented electrical steel sheet is improved in magnetic properties only when the easy magnetization axis <001> is aligned in the rolling direction, so that in principle, good magnetic properties cannot be obtained only by selecting the {110} plane. Therefore, rolling conditions and annealing conditions that can obtain good magnetic properties by a method using surface energy are extremely limited, and as a result, the obtained magnetic properties must be unstable.
[0009]
Furthermore, in the method using the surface energy, the final finish annealing must be performed while suppressing the formation of the surface oxide layer. For example, an annealing separator such as MgO cannot be applied and annealed. An oxide film similar to that of a normal grain-oriented electrical steel sheet cannot be formed. For example, a forsterite film is a film formed when MgO is applied as a main component as an annealing separator, but this film not only gives tension to the surface of the steel sheet, but also a phosphate that is further applied and baked thereon. It is responsible for ensuring the adhesion of the insulation tension coating mainly composed of. Accordingly, in the absence of such a forsterite film, the iron loss is greatly deteriorated.
[0010]
In addition, a technique for secondary recrystallization by using a hot rolling reduction ratio of 30% or more and a hot rolled sheet thickness of 1.5 mm or less without using an inhibitor component has been proposed in JP-A-11-61263. However, the degree of Goss orientation accumulation obtained with this technique is only low compared to the technique using conventional inhibitors.
[0011]
In this regard, the inventors are a manufacturing technique that does not use an inhibitor that avoids the problems associated with high-temperature slab heating before hot rolling as described above, and does not use an inhibitor and utilizes surface energy. A new manufacturing technology for grain-oriented electrical steel sheets that solves the problem of the limited steel sheet thickness, which is necessarily associated with the method, has been developed and proposed in Japanese Patent Application Laid-Open No. 2000-129356.
[0012]
In the conventional method using an inhibitor, as described above, it was necessary to heat the slab at a high temperature. However, the technique described in JP-A-2000-129356 does not contain an inhibitor component, and thus it is not necessarily at a high temperature. There is no need to perform slab heating, and it is possible to manufacture grain-oriented electrical steel sheets at a lower cost than before.
[0013]
Thus, recently, in the manufacture of grain-oriented electrical steel sheets, in addition to magnetic properties, it has been strongly desired to supply products at low cost. In addition to cost reduction in equipment, the yield of products themselves It has become an important issue to improve.
From the viewpoint of improving the yield, it is an important issue how to prevent the occurrence of ear cracks at the hot rolled plate edge.
[0014]
Regarding the technology for preventing the ear cracks in the hot rolling process at the time of manufacturing the grain-oriented electrical steel sheet, for example, Japanese Patent Application Laid-Open No. 55-62124 discloses finish rolling in the hot rolling process of unidirectional silicon steel continuous cast pieces. A hot rolling method of a unidirectional silicon steel sheet is disclosed in which the difference between the start temperature and the finish rolling end temperature, that is, the temperature drop during hot finish rolling is controlled to 220 ° C. or less.
In addition, JP-A-60-145204, JP-A-60-200916, JP-A-61-71104, JP-A-62-196328 and JP-A-5-138207 disclose hot A hot rolling method for grain-oriented silicon steel in which ear cracks are prevented by adjusting the shape of the side surface of the sheet bar during rolling is disclosed. In these techniques, a notch-shaped recess is formed at the grain boundary part of the crystal that has grown coarsely by high-temperature heating of the slab, and this becomes the starting point of the ear crack. Is.
[0015]
In addition, a method of regulating the final rolling reduction ratio of hot rough rolling described in JP-A-54-31024, a method of applying width reduction and horizontal reduction after slab heating described in JP-A-3-133501, A method for controlling a slab cast structure described in JP-A-3-243244 and a method for converting a slab cross-sectional shape described in JP-A-61-3837 to a special shape have been proposed.
Furthermore, JP-A-60-200916 proposes a method for producing grain-oriented silicon steel sheets in which slabs are heated and then subjected to 5-40% width reduction in the hot rough rolling stage to prevent ear cracks. Has been.
[0016]
However, these ear crack reduction technologies are premised on slab heating at a high temperature of 1250 ° C or higher, and when applied to slab heating at a low temperature of less than 1250 ° C, the effect of reducing ear cracks is hardly recognized. It was.
[0017]
[Problems to be solved by the invention]
The present invention advantageously solves the above problem, and effectively reduces the occurrence of ear cracks during hot rolling, which is a concern when a slab containing no inhibitor is heated at a low temperature of less than 1250 ° C. Then, it aims at proposing the advantageous manufacturing method of the grain-oriented electrical steel sheet which can manufacture a grain-oriented electrical steel sheet with high yield.
[0018]
[Means for Solving the Problems]
The elucidation process of the present invention will be described below.
Now, as a result of intensive studies on the mechanism of secondary recrystallization of goth-oriented grains, the inventors have found that grain boundaries having an orientation difference angle of 20 to 45 ° in the primary recrystallized structure play an important role. And reported on Acta Material 45 (1997), p. 1285.
[0019]
FIG. 1 shows the existence frequency (%) with respect to each orientation grain of the grain boundary where the orientation difference angle in the primary recrystallized structure of the grain-oriented electrical steel sheet is 20 to 45 °, and the Goss orientation grain has the highest frequency.
And a grain boundary with a misorientation angle of 20 to 45 ° is a high energy grain boundary according to experimental data (AIME Transaction 188 (1949) 368) by C. G. Dunn et al. This high energy grain boundary has a messy structure with a large free space within the grain boundary. Grain boundary diffusion is a process in which atoms move through the grain boundary. Therefore, grain boundary diffusion is faster in a high energy grain boundary with a large free space in the grain boundary.
It is known that secondary recrystallization occurs with the growth of precipitates called inhibitors, which is controlled by diffusion rate. Precipitation on high-energy grain boundaries preferentially progressed during finish annealing, so that the pinning was preferentially released and grain boundary migration started, indicating a mechanism for the growth of goth grains.
[0020]
The inventors further developed this research, and the essential factor of secondary recrystallization of Goss-oriented grains is the distribution state of high energy grain boundaries in the primary recrystallization structure, and the role of inhibitors is high energy. It has been found that there is a difference in moving speed between the grain boundary and other grain boundaries.
Therefore, according to this theory, secondary recrystallization can be performed if a difference in the moving speed of the grain boundary can be generated without using an inhibitor.
[0021]
Now, the impurity elements present in steel are easy to segregate at the grain boundaries, especially at high energy grain boundaries, so when there are many impurity elements, there is no difference in the moving speed between the high energy grain boundaries and other grain boundaries. It is thought that there is.
In this regard, if the influence of the impurity elements as described above can be eliminated by increasing the purity of the material, the inherent difference in the moving speed depending on the structure of the high energy grain boundary becomes obvious, and the two goss-oriented grains are It is considered that next recrystallization is possible.
[0022]
Furthermore, in order to enable stable secondary recrystallization using the grain boundary moving speed difference, it is important to keep the primary recrystallization structure as uniform as possible in the particle size distribution. This is because, when a uniform grain size distribution is maintained, the crystal grains other than the Goss orientation grains have a low frequency of low energy grain boundaries with a low grain boundary moving speed, and thus the grain growth is suppressed. This is because by the so-called Texture Inhibition effect, secondary recrystallization as selective grain growth of Goss-oriented grains where the frequency of high-energy grain boundaries having a large grain boundary moving speed is maximum proceeds.
On the other hand, when the grain size distribution is not uniform, normal grain growth using the grain size difference between adjacent crystal grains as a driving force occurs. As a result, the Texture Inhibition effect is not exhibited, and the selective growth of goth-oriented grains does not occur.
[0023]
However, in industrial production, it is practically difficult to completely remove the inhibitor component, so it is inevitably contained. However, when the slab heating temperature before hot rolling is high, a small amount of solid solution dissolved after heating As a result of the non-uniform fine precipitation of the inhibitor component as an impurity during hot rolling, grain boundary migration is locally suppressed, the particle size distribution becomes extremely nonuniform, and the development of secondary recrystallization is inhibited. Therefore, it is the first to reduce the inhibitor component, but in order to make it harmless by avoiding fine precipitation of a minute amount of the inhibitor component inevitably mixed, the slab heating temperature before hot rolling is within the range that can be rolled. It is effective to keep it as low as possible.
[0024]
This technique is completely opposite to the conventional secondary recrystallization technique in that it eliminates precipitates and impurities at the grain boundaries, and is different from the technique that uses surface energy. Even if it exists, secondary recrystallization can be caused satisfactorily.
[0025]
However, by lowering the slab heating temperature, a new problem arises that the frequency of occurrence of ear cracks increases due to hot rolling, and the depth also increases.
That is, when a slab containing no inhibitor element was heated in a gas combustion furnace and then hot rolled, when the slab heating temperature was as high as 1250 ° C or higher, ear cracks hardly occurred, but the slab heating temperature was 1250 ° C. Ear cracks occurred when the temperature was lower than 0 ° C.
[0026]
Further, the ear cracks are periodically generated in the longitudinal direction, and the interval between the hot rolled plates corresponds to the skid interval in the gas combustion furnace.
That is, the interval at which the ear cracks occur in the steel sheet after hot rolling was substantially equal to the interval corresponding to the skid position of the gas combustion furnace (skid interval × hot rolled plate length / slab length).
[0027]
The main cause of this ear crack is that it does not occur when the slab heating temperature is high, so it occurs by a mechanism different from the ear cracking in hot rolling of conventional grain-oriented electrical steel sheets containing inhibitors and a high slab heating temperature. It is thought that.
[0028]
Therefore, the inventors first thought that the ear cracks were caused by a decrease in the steel plate temperature during hot rolling, and the ear cracks occurred before the finish rolling as described in JP-A-9-70602. The relationship between the temperature of the rough rolled material of the slab (hereinafter referred to as a sheet bar) and the ear cracks was investigated.
As a result, the temperature of the seat bar increased and decreased at intervals corresponding to the skid interval while gradually decreasing from the front end portion to the rear end portion in the longitudinal direction. Therefore, the minimum temperature at the skid interval portion at the front end portion in the longitudinal direction was higher than the maximum temperature at the skid interval portion at the rear end portion in the longitudinal direction.
However, the ear cracks occurred in the same manner at intervals corresponding to the skid interval over the entire length in the longitudinal direction.
From this result, it was found that the cause of the occurrence of the ear crack was not merely due to the decrease in the steel plate temperature.
[0029]
Next, an experiment was conducted in which the skid interval was changed using a vertical induction heating furnace in which a slab was placed vertically and heated. In this case, the lower end of the plate width in the vertical induction heating furnace is greatly affected by the skid, and the ear cracks are likely to occur. Here, hot finish rolling was performed with a constant sheet bar thickness when the slab after heating was roughly rolled, and the occurrence of ear cracks in the obtained hot-rolled sheet was investigated.
As a result, it was found that if the skid interval during slab heating is wide, it is difficult for ear cracks to occur. That is, even when the maximum temperature and the minimum temperature (usually corresponding to the skid portion) within the skid interval are substantially the same, the occurrence of ear cracks at the skid portion is reduced when the skid interval is wide.
From this result, it was considered that the occurrence of the ear crack is related to the temperature gradient in the vicinity of the skid portion in the longitudinal direction of the edge portion.
[0030]
Therefore, as described above, based on the assumption that the ear cracks occurred before the finish rolling, an experiment was performed to change the interval between the positions corresponding to the skids immediately before the finish rolling. The interval was changed by changing the reduction ratio by rough rolling and changing the thickness of the sheet bar. Note that the temperature gradient in the vicinity of the skid-corresponding position in the longitudinal direction of the edge portion becomes gentler as the sheet bar thickness becomes thinner.
As a result of examining the hot-rolled sheet after finish rolling, it has been found that when the sheet bar thickness is thin, that is, when the interval corresponding to the skid in the sheet bar is increased, the occurrence of ear cracks is reduced.
That is, when hot rolling the directional electromagnetic steel slab into a hot-rolled sheet, it becomes clear that the ear cracking is improved by reducing the longitudinal temperature gradient in the sheet bar immediately before finish rolling. It was.
[0031]
The reason for this is not clear, but is thought to be as follows.
Many empirical formulas for deformation resistance are expressed by the following formulas.
[Expression 1]

Where σ is deformation resistance, ε is strain,
[Outside 1]

Is the strain rate, T is the temperature, and C and A are constants.
Differentiating this equation with temperature,
[Expression 2]

It becomes.
In other words, the change in the deformation resistance in the longitudinal direction is larger at a lower temperature if the temperature change is the same. Therefore, it is considered that the change in deformation resistance due to the temperature gradient in the longitudinal direction becomes larger in the slab low-temperature heating, and the ear cracks frequently occur.
[0032]
Further, since the temperature gradient in the longitudinal direction is larger when it is not significantly reduced, that is, when it is not stretched in the longitudinal direction, the gradient of deformation resistance is greater during rough rolling. Therefore, during rough rolling, it is considered that a crack that is the starting point of the ear crack is generated even if it does not become an ear crack because the plate is thick. This is also considered to be one of the reasons that ear cracks are likely to occur in low-temperature slab heating where rough rolling is performed at a low temperature.
[0033]
On the other hand, in the latter stage of finish rolling, the rolling temperature is further lowered, but it is sufficiently stretched in the longitudinal direction, and the length corresponding to the skid interval is also sufficiently long. It is thought that ear cracks are less likely to occur.
Therefore, when performing slab heating at a low temperature as in the present invention, the stage where ear cracks are most likely to occur is the stage before finish rolling that is in the middle of hot rolling. It is considered that the generation of the ear cracks was suppressed by making the temperature gradient in the vicinity gentle.
[0034]
In the case of not containing an inhibitor as in the present invention, even if the slab is heated at a low temperature, the crystal growth is not suppressed after the slab heating, and the particle size becomes coarse. This is considered to have further promoted the occurrence of ear cracks by the mechanism described above, and increased the occurrence of ear cracks.
From the above, it is important to reduce the temperature gradient in the longitudinal direction of the seat bar in order to reduce the ear cracks.
The present invention has been completed based on the above findings and further studies.
[0035]
  That is, the gist configuration of the present invention is as follows.
1. A steel slab with a composition containing C: 0.080% or less, Si: 2.0-8.0%, and Mn: 0.005-3.0%, with Al reduced to less than 100 ppm and N, S, and Se reduced to 50 ppm or less respectively. , Heated to a temperature of less than 1250 ° C, hot rolled, hot-rolled sheet annealed as needed, then cold-rolled at least once with intermediate or intermediate annealing, followed by decarburization annealing After manufacturing the grain-oriented electrical steel sheet through a series of processes for applying a final finish annealing after applying an annealing separator as required,
  Each skid interval in the slab heating step is D_i (M), ΔT is the temperature difference within the skid interval on the rough rolling delivery side_i (° C), when the rolling reduction of hot rough rolling is R (%),D above _i , ΔT _i And R are adjusted to each other,(1)
    T_i '= ΔT_i × (1-R ÷ 100) ÷ D_i         --- (1)
Calculated byImmediately after rough rollingT_iThe maximum value T ′ of ′ is 10.0 ℃ / m or lessControlA method for producing a grain-oriented electrical steel sheet, comprising:
[0036]
2. In the above 1, the steel slab further comprises, in mass%, Ni: 0.005 to 1.50%, Sn: 0.01 to 0.50%, Sb: 0.005 to 0.50%, Cu: 0.01 to 1.50%, P: 0.005 to 0.50%, and Cr: A method for producing a grain-oriented electrical steel sheet, comprising a composition containing one or more selected from 0.01 to 1.50%.
[0037]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be specifically described.
First, the reason why the component composition of the slab, which is a material, is limited to the above range in the present invention will be described. In addition, unless otherwise indicated, the "%" display regarding a component means the mass% (mass%).
C: 0.080% or less
If the amount of C exceeds 0.080%, it becomes difficult to reduce to 50 ppm or less where magnetic aging does not occur. Therefore, C is limited to 0.080% or less.
Si: 2.0 to 8.0%
Si is an active ingredient that increases the specific resistance of steel and reduces iron loss. However, if the content exceeds 8.0%, the cold rolling property is impaired. On the other hand, if it is less than 2.0%, a high specific resistance cannot be obtained. Since a sufficient iron loss reduction effect could not be obtained, the Si content was limited to the range of 2.0 to 8.0%. Mn: 0.005 to 3.0%
Mn is an element useful for improving hot workability. However, if the content is less than 0.005%, the effect of addition is poor. On the other hand, if it exceeds 3.0%, the magnetic flux density is lowered. The range is ˜3.0%.
[0038]
Al: Less than 100 ppm, N, S, Se are each 50 ppm or less
Further, it is indispensable for good secondary recrystallization to reduce the impurity element Al to less than 100 ppm and N, S, and Se to 50 ppm or less, preferably 30 ppm or less. In addition, it is effective to reduce the iron loss of Ti, Nb, B, Ta, V, etc., which are nitride-forming elements, to 50 ppm or less, respectively, and to ensure good workability.
[0039]
As described above, the essential component and the suppressing component have been described. However, in the present invention, other elements described below can be appropriately contained.
Ni: 0.005 to 1.50%, Sn: 0.01 to 0.50%, Sb: 0.005 to 0.50%, Cu: 0.01 to 1.50%, P: 0.005 to 0.50%, Cr: 0.01 to 1.50%
Ni is a useful element that improves the magnetic properties by improving the hot-rolled sheet structure. However, if the content is less than 0.005%, the amount of improvement in magnetic properties is small. On the other hand, if it exceeds 1.50%, secondary recrystallization becomes unstable and the magnetic properties deteriorate, so the Ni content is set to 0.005 to 1.50%.
Sn, Sb, Cu, P, and Cr are elements useful for improving the iron loss, but if any of them does not satisfy the lower limit of the above range, the effect of improving the iron loss is small, while the upper limit is exceeded. And secondary recrystallized grains are inhibited from development, Sn: 0.01 to 0.50%, Sb: 0.005 to 0.50%, Cu: 0.01 to 1.50%, P: 0.005 to 0.50%, Cr: 0.01 to 1.5% Include in the range.
[0040]
Next, the manufacturing process of the present invention will be described.
The molten steel adjusted to the above preferred component composition is refined by a known method using a converter, electric furnace, etc., and if necessary, after vacuum treatment, etc., using a normal ingot forming method or continuous casting method Manufacture slabs. Alternatively, a thin cast piece having a thickness of 100 mm or less may be directly produced by using a direct casting method.
[0041]
The slab is heated by a normal method and then subjected to hot rolling.
At this time, it is important that the slab heating temperature is less than 1250 ° C. This is because it is necessary to lower the slab heating temperature in order to make the primary recrystallized structure uniform with a uniform grain size by making the crystal structure finer and inevitable the harmful effects of inhibitor components that are inevitably mixed. is there. Moreover, the amount of scale produced | generated at the time of hot rolling can also be reduced by restraining the slab heating temperature before hot rolling to less than 1250 degreeC.
[0042]
Slab heating may use a gas combustion furnace or an electric heating furnace or both. The slab heated in the heating furnace is subjected to hot rough rolling and subsequently hot finish rolling to obtain a hot rolled sheet.
At this time, in order to prevent ear cracks due to hot rolling, it is important to reduce the temperature gradient in the longitudinal direction of the seat bar. This temperature gradient is mainly caused by skids in the heating furnace.
[0043]
Therefore, in order to prevent ear cracks during hot rolling, the temperature gradient of the seat bar should be regulated, but the actual temperature measurement in the longitudinal direction of the seat bar is performed by a radiation thermometer, etc. As a result, the temperature measurement data fluctuates with a period considerably smaller than the length corresponding to the skid interval. For this reason, it is virtually impossible to obtain an accurate temperature gradient.
[0044]
Therefore, in the present invention, the regulation is made as described below. By the method described below, the temperature of the seat bar can be sufficiently grasped by the temperature measured by the radiation thermometer, and the method described below is also a feature of the present invention.
Here, the skid refers to the one that directly touched the slab for 5 minutes or more and supported the slab immediately before the slab extraction in the last heating furnace used for heating the slab. That is, the mobile beam used for slab extraction is not considered skid. When the contact area between the slab and the skid is large, the center of the contact area is set as the skid position.
[0045]
First, the position of the skid from the tip in the rolling direction of the slab₁ A₂ --- A_n (N is the number of skids). A₀ = 0, A_{n + 1} = Slab length.
The distance between each i th skid is D_i = (A_{i + 1} -A_i-1) ÷ 2 (i = 1, 2, --n).
In addition, as the position of the skid corresponding to the seat bar, a_i = Α × A_i (I = 1, 2, --n).
Here, α is (sheet bar length ÷ slab length).
If the rolling reduction ratio of the rough rolling, that is, 100 × (slab thickness−sheet bar thickness) ÷ slab thickness is R, α is slightly shifted by the width reduction during rough rolling, but (1 ÷ (1 -R ÷ 100)).
Temperature difference ΔT in the i-th skid (i = 1, 2, --n)_i A_i -(A_i -A_i-1 ) × 3 ÷ 4 and a_i + (A_{i + 1} -A_i ) The difference between the maximum value and the minimum value of the temperature of the seat bar in the section of 3 × 4.
The above relationship is illustrated in FIG.
[0046]
For n skids, the following equation (1)
T_i '= ΔT_i × (1-R ÷ 100) ÷ D_i         --- (1)
And the maximum value among them is T ′.
In order to prevent ear cracks, T which is an index of temperature gradient is used._i The maximum value T ′ of ′ is controlled so as to satisfy the relationship of the following equation.
T'≤10.0 (℃ / m)
[0047]
In order to satisfy the above conditions, there are methods such as changing the skid interval of the heating furnace, reducing the temperature difference between the skid portion of the heating furnace and the temperature, and increasing the rolling reduction of rough rolling.
The temperature of the sheet bar is assumed to be the temperature immediately after the rough rolling because the temperature gradient during the rough rolling is considered to be affected by the ear cracks. Further, the temperature measurement position of the seat bar may be anywhere between 100 mm from the end in the width direction, but the distance from the end in the width direction to the temperature measurement position is the same for each temperature measurement position in the longitudinal direction. The temperature measuring method may be a radiation thermometer, and is not specified. What is important is the temperature difference ΔT in the longitudinal direction.
In the hot-rolled sheet manufactured by such a method, the amount of cut-off due to the occurrence of ear cracks is small, and the product yield is remarkably improved.
[0048]
Next, hot-rolled sheet annealing is performed as necessary. In order to develop a goth structure on the product plate to a high degree, the hot-rolled sheet annealing temperature is preferably in the range of 800 to 1100 ° C. This is because when the annealing temperature of the hot-rolled sheet is less than 800 ° C, the band structure in the hot-rolling remains and it becomes difficult to realize the primary recrystallized structure of the sized particles, thereby inhibiting the development of secondary recrystallization. On the other hand, when the hot-rolled sheet annealing temperature exceeds 1100 ° C, the unavoidably mixed inhibitor components dissolve and re-precipitate non-uniformly during cooling, making it difficult to achieve a sized primary recrystallized fabric. This is also because the development of secondary recrystallization is inhibited. Further, when the hot-rolled sheet annealing temperature exceeds 1100 ° C., the grain size after hot-rolled sheet annealing is too coarse, which is extremely disadvantageous for realizing a primary recrystallized structure of sized particles.
[0049]
After hot-rolled sheet annealing, cold rolling is performed once or two or more times with intermediate annealing, followed by decarburization annealing to reduce C to 50 ppm or less, preferably 30 ppm or less, which does not cause magnetic aging.
In the above cold rolling, the rolling temperature is raised to 100 to 250 ° C., and the aging treatment in the range of 100 to 250 ° C. is performed once or a plurality of times during the cold rolling. However, it is effective in developing Gothic tissue.
[0050]
The decarburization annealing after the final cold rolling is preferably performed at a temperature of 700 to 1000 ° C. using a wet atmosphere. Moreover, you may use together the technique which increases Si amount by the siliconization method after decarburization annealing.
Then, if necessary, an annealing separator is applied and a final finish annealing is performed to develop a secondary recrystallized structure. The final finish annealing needs to be performed at 800 ° C. or higher for the secondary recrystallization. However, the heating rate up to 800 ° C. does not have a great influence on the magnetic properties, and any conditions may be used.
[0051]
Thereafter, flattening annealing is performed to correct the shape.
Then, after the above-described flattening annealing, for the purpose of improving the iron loss, it is advantageous to provide an insulating coating that imparts tension to the steel sheet surface.
Furthermore, it goes without saying that known magnetic domain refinement techniques can be applied.
[0052]
【Example】
Example 1
Slabs having thicknesses of 180 mm, 210 mm, and 240 mm were manufactured by continuous casting from molten steels having compositions indicated by steel symbols A, B, and C in Table 1, respectively. Next, these slabs were heated to 1200 ° C. in a gas combustion furnace, and then rolled into a sheet bar, followed by finish rolling into a hot rolled sheet having a thickness of 2.4 mm.
At that time, the skid interval of the heating furnace, the rough rolling reduction ratio, and the like were as shown in Table 2. No. 1 to 9 can be changed by changing the skid interval and slab thickness, No. 10 to 12 can be changed by changing the thickness of the seat bar, and No. 13 to 15 can be changed by changing the temperature difference ΔT. , T ′ was changed. The temperature of the sheet bar was measured in the longitudinal direction at a position 20 mm from the width end.
The results of examining the maximum depth of the ear cracks of the obtained hot rolled sheet are also shown in Table 2.
[0053]
[Table 1]

[0054]
[Table 2]

[0055]
As is apparent from Table 2, in all of the inventive examples in which T ′ is 10 ° C./m 2 or less, the ear crack maximum depth is 5 mm or less, and the occurrence of the ear crack is remarkably reduced.
On the other hand, in all of the comparative examples in which T ′ exceeded 10.0 ° C./m 2, the ear cracks were inevitably generated with a maximum depth exceeding 10 mm.
[0056]
Example 2
Each slab having a thickness of 220 mm was manufactured by continuous casting from the molten steel having the compositions indicated by steel symbols A to V in Table 1. Next, these slabs were heated to 1180 ° C. in a gas combustion furnace and then rolled into a sheet bar with a thickness of 40 mm by rough rolling, and subsequently rolled into a hot rolled sheet with a thickness of 2.3 mm by finish rolling and wound in a coil shape. .
Further, the steel symbol D slab was heated to 1180 ° C. in a gas combustion furnace, further heated to 1350 ° C. in an induction heating furnace, and then subjected to the same hot rolling as a comparative example.
In all slab hot rolling at this time, T ′ was set to 10.0 ° C./m 2 or less.
As a result, the maximum depth of the ear crack was 5 mm or less in all the hot-rolled sheets.
[0057]
Next, all these hot-rolled sheets were annealed at 1000 ° C for 30 seconds, quenched at a rate of 35 ° C / s, pickled, and then warm-rolled at 240 ° C to a thickness of 0.34 mm. Finished.
After degreasing treatment, H₂: 50 vol%, N₂: Decarburization annealing at 840 ° C for 2 minutes in an atmosphere of 50 vol% and dew point: 57 ° C.
Next, MgO and TiO₂An annealing separator with 5 mass% added to each side of the steel sheet, 8 g / m per side²After applying, N as the final finish annealing₂After holding at 850 ° C for 48 hours in gas, the temperature was raised to 900 ° C at a rate of 5 ° C / h, and then the atmospheric gas₂H from gas₂Change to gas and raise the temperature to 1120 ° C at a rate of 25 ° C / h.₂N from gas₂: 25 vol%, H₂: Changed to 75 vol% mixed gas, heated to 1190 ° C at a rate of 25 ° C / h, then H₂After changing to gas and holding at 1190 ° C for 8 hours, H up to 600 ° C₂The temperature was lowered in gas, and the temperature was lowered in Ar gas from 600 ° C.
After the above final finish annealing, the unreacted annealing separator was removed, and then magnesium phosphate containing 50% colloidal silica was applied as a tension coating, followed by baking at 840 ° C. for 30 seconds to obtain a product plate.
About the product plate thus obtained, the magnetic flux density B₈ And iron loss W_17/50 Was measured, and film adhesion was evaluated. The coating adhesion was evaluated by the bending peel diameter (the minimum bending diameter at which the steel sheet was wound around a round bar and the film was not peeled). The results are shown in Table 3.
[0058]
[Table 3]

[0059]
As shown in the table, the steel symbols Q to V containing the inhibitor element exceeding the upper limit of the present invention and the symbol D heated to 1350 ° C. by slab heating had deteriorated magnetic properties.
On the other hand, all of the steel symbols A to P in which the component composition and the slab heating temperature satisfy the appropriate range of the present invention were both good in magnetic properties and coating properties.
[0060]
【The invention's effect】
Thus, according to the present invention, when producing the grain-oriented electrical steel sheet, when the slab heating temperature is suppressed to less than 1250 ° C., it is possible to effectively reduce the occurrence of ear cracks that are concerned in the hot rolling process. As a result, the end cut-off amount due to such ear cracks can be remarkably reduced, and the product yield can be remarkably improved, which is extremely useful industrially.
[Brief description of the drawings]
FIG. 1 is a graph showing the existence frequency (%) of each grain at a grain boundary having a misorientation angle of 20 to 45 ° in the primary recrystallization structure of a grain-oriented electrical steel sheet.
[Figure 2] Temperature difference ΔT_i It is a calculation point explanatory drawing.

Claims (2)

A steel slab with a composition containing C: 0.080% or less, Si: 2.0-8.0%, and Mn: 0.005-3.0%, with Al reduced to less than 100 ppm and N, S, and Se reduced to 50 ppm or less. , Heated to a temperature of less than 1250 ° C, hot rolled, hot-rolled sheet annealed as necessary, then cold-rolled at least once with intermediate or intermediate annealing, followed by decarburization annealing After manufacturing the grain-oriented electrical steel sheet through a series of processes for applying a final finishing annealing after applying an annealing separator as required,
When each skid interval in the slab heating step is D _i (m), a temperature difference within the skid interval on the rough rolling delivery side is ΔT _i (° C.), and a rolling reduction ratio of hot rough rolling is R (%) By adjusting the above D _i , ΔT _i and R to each other, the following equation (1)
T _i ′ = ΔT _i × (1−R ÷ 100) ÷ D _i --- (1)
A method for producing a grain-oriented electrical steel sheet, characterized in that the maximum value T ′ of T _i ′ immediately after the rough rolling calculated by the step is controlled to 10.0 ° C./m or less.   The steel slab according to claim 1, wherein the steel slab further comprises, in mass%, Ni: 0.005 to 1.50%, Sn: 0.01 to 0.50%, Sb: 0.005 to 0.50%, Cu: 0.01 to 1.50%, P: 0.005 to 0.50%, and Cr. : A method for producing a grain-oriented electrical steel sheet, wherein the composition contains one or more selected from 0.01 to 1.50%.

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