JP4119635B2 - Method for producing mirror-oriented electrical steel sheet with good decarburization - Google Patents

Description

【００１５】
製品板において炭素量が２５ｐｐｍを超えると、磁気時効、すなわち、経時変化に伴う磁性劣化が起きるので、脱炭焼鈍板の炭素量は２５ｐｐｍ以下に制御する必要がある。
表１より、脱炭焼鈍板炭素量が２５ｐｐｍ以下を満たす温度範囲は、７７０〜８６０℃であることがわかる。この温度範囲の外、すなわち、温度７７０℃未満の場合には、炭素が拡散律速となり、短時間に鋼板表面まで移動できなくなるため脱炭不良となり、一方、温度８６０℃を超える場合には、外部酸化に近い形態の非常に緻密なＳｉＯ₂酸化層が鋼板表面に形成され、炭素がこの酸化層を透過し得なくなるため、脱炭不良となるものと推察される。
【００１６】
一方、磁束密度Ｂ₈に関しては、焼鈍温度が高い方が良好であり、８３０℃以上で１．９０Ｔ以上、さらに、８７０℃以上で１．９４Ｔ以上となり非常に良好である。焼鈍温度が高い方が磁束密度が良好である理由に関しては、現時点で、詳細は不明であるが、以下のように考えられる。
すなわち、今回の鏡面方向性電磁鋼板の製造工程においては、脱炭焼鈍工程で、ある程度緻密なＳｉＯ₂酸化層を形成させ、この酸化層により、仕上げ焼鈍中のインヒビターを制御し、良好な二次再結晶を実現している。
【００１７】
脱炭焼鈍温度を高温にすると、ＳｉＯ₂酸化層がより緻密に形成されるが、この酸化層を緻密にすることが、仕上げ焼鈍中のインヒビターの弱体化の阻止に、良好な影響を与えているものと推察される。
以上より、炭素量と磁束密度の観点から、総合的な最適脱炭焼鈍温度を考えると、表１より８３０〜８６０℃（試料５、６）が適正である。しかしながら、これらの試料では、磁束密度に関して十分高いとは言えず、その意味で、脱炭性の確保と高磁束密度化の両立は困難であった。
【００１８】
そこで、本発明者らは、脱炭焼鈍均熱温度を前段と後段に分け、前段において脱炭促進、後段において高磁束密度化促進、という機能分離をすることにより、従来、実現が困難であった前記課題を解決すべく検討を試みた。以下に、その詳細を説明する。
前記試験で用いた成分及び工程の冷延板を用い、以下のような試験を行った。すなわち、冷延板を、水素と窒素を含有する湿潤ガス中（Ｐ_H2O／Ｐ_H2＝０．１３）において、まず、脱炭焼鈍炉の前段において、８３０℃，７５秒の焼鈍を行った。続いて脱炭焼鈍炉の後段において、温度を種々変更し、同一雰囲気にて、１５秒間の焼鈍を実施した。
【００１９】
その後、アンモニアガス中にて鋼中窒素量を０．０２％まで高め、インヒビターを強化した。この脱炭焼鈍板に、アルミナを主成分とする焼鈍分離剤を、水スラリー状で塗布した後、仕上げ焼鈍を施した。仕上げ焼鈍は、１２００℃までは、窒素１００％の雰囲気中で１５℃／ｈｒの昇温速度で行い、１２００℃で水素１００％に切り替え、２０時間焼鈍を行った。
【００２０】
以上の工程により作製された鏡面材につき、水洗、試料剪断の後、さらに、歪取り焼鈍を行い、ＳＳＴ法にて磁気測定を行った。脱炭焼鈍後の炭素量及び歪取り焼鈍後の磁束密度Ｂ₈の値を表２に示す。
【００２１】
【表２】

【００２２】
脱炭焼鈍の前段にて脱炭が進行したため、脱炭性に関してはいずれの条件においても良好であった。さらに、脱炭焼鈍炉後段の焼鈍温度を、前段の温度よりも１０℃以上高くした試料２〜８においては、磁束密度Ｂ₈に関しても１．９３Ｔ以上であり、良好であった。試料９において磁束密度の低下した理由は、後段の温度が高過ぎ、一次再結晶粒径が粗大化し過ぎて、良好な二次再結晶粒が得られなかったものと推定される。
【００２３】
以上より、本発明者らは、脱炭焼鈍温度を前段と後段の二段に機能分離することにより、従来困難であった脱炭性の確保と高磁束密度化を両立できることを新規に知見し、本発明を完成させた。
続いて、本発明における実施形態について説明する。基本的な製造法としては、田口、坂倉等によるＡｌＮとＭｎＳを主インヒビターとして用いる製造法（例えば、特公昭４０−１５６４４号公報）、または、小松等による（Ａｌ、Ｓｉ）Ｎを主インヒビターとして用いる製造法（例えば、特公昭６２−４５２８５号公報）を適用すればよい。
【００２４】
Ｓｉは電気抵抗を高め、鉄損を低減する上で重要な元素である。含有量が４．０％を超えると、冷間圧延時に材料が割れやすくなり、圧延不可能となる。一方、Ｓｉ量を下げると、仕上げ焼鈍時にα→γ変態が生じ、結晶の方向性が損なわれるので、実質的に結晶の方向性に影響を及ぼさない２．０％を下限とする。
酸可溶性ＡｌはＮと結合して、ＡｌＮまたは（Ａｌ、Ｓｉ）Ｎとして、インヒビターとして機能するうえで必須の元素である。磁束密度が高くなる０．０１〜０．０５％を限定範囲とする。Ｎは、製鋼時に０．０１％を超えて存在すると、鋼板中にブリスターと呼ばれる空孔が生じるので、０．０１％を上限とする。
【００２５】
Ｍｎ量とＳ量に関しては、二次再結晶を良好なものとするための適正なインヒビター量を確保する観点から、Ｍｎ０．３％以下、Ｓ０．０５％以下とすることが好ましい。他のインヒビター構成元素として、Ｂ、Ｂｉ、Ｓｅ、Ｐｂ、Ｍｏ、Ｓｂ、Ｓｎ、Ｔｉ、Ｖ等を添加しても構わない。
前記成分の溶鋼は、通常の工程により熱延板とされるか、もしくは、溶鋼を連続鋳造して薄帯とされる。前記熱延板または連続鋳造薄帯は、直ちに、もしくは、短時間の焼鈍を経て冷間圧延される。この短時間焼鈍は、７５０〜１２００℃の温度域で３０秒〜３０分間行われ、製品の磁気特性を高めるために有効である。製品における所望の特性レベルとコストを勘案して採否を決めるとよい。
【００２６】
冷間圧延は、基本的には、特公昭４０−１５６４４号公報に開示されているように、最終冷延圧下率８０％以上の冷間圧延を行なえばよい。
冷間圧延後の鋼板に対して、鋼中に含まれる炭素を除去するために、湿水素雰囲気中で脱炭焼鈍を施す。実施例１に示すように、鏡面方向性電磁鋼板を製造するためには、脱炭焼鈍の酸化度（Ｐ_H2O／Ｐ_H2）を、脱炭を行いかつＦｅ系酸化物（Ｆｅ₂ＳｉＯ₄，ＦｅＯ等）を生成させない酸化度、すなわち、０．０１以上０．２未満に設定することが必要である。
【００２７】
本発明の主要点である脱炭焼鈍温度に関しては、前段（均熱温度Ｔ１（℃））と後段（均熱温度Ｔ２（℃））に分け、それぞれ、７７０≦Ｔ１≦８６０、Ｔ１＋１０≦Ｔ２≦９５０の範囲とすることが必要である。この理由は、Ｔ１がこの範囲外であると、脱炭不良を引き起こし、Ｔ２が前記範囲外であると、製品板にて高い磁束密度が得られないからである。この範囲内で、さらに好ましい範囲は、８００≦Ｔ１≦８５０、Ｔ１＋２０≦Ｔ２≦９３０である。
【００２８】
脱炭焼鈍における前段焼鈍については、脱炭を進行させるため、３０秒以上保定することが好ましい。また、後段の焼鈍に関しては、磁束密度向上のため、３秒以上保定することが好ましい。
【００２９】
前記脱炭焼鈍板に（Ａｌ、Ｓｉ）Ｎを主インヒビターとして用いる製造法（例えば、特公昭６２−４５２８５号公報）においては、窒化処理を施す。この窒化処理の方法は、特に限定されるものではないが、アンモニア等の窒化能のある雰囲気ガス中にストリップを通過させる方法等を採用することができる。窒化量としては０．００５％以上、望ましくは、全窒素量として、鋼中のＡｌ当量以上を窒化すればよい。
【００３０】
これらの脱炭焼鈍板を積層する際に、焼鈍分離剤としてアルミナを、水スラリー法、もしくは、静電塗布法等によりドライコートする。この積層した板を仕上げ焼鈍し、二次再結晶と窒化物の純化を行う。
二次再結晶を、特開平２−２５８９２９号公報に開示されるように、一定の温度で保持する等の手段により所定の温度域で行うことは、磁束密度を高める上で有効である。二次再結晶完了後、窒化物の純化と表面の平滑化を行うために、水素１００％の雰囲気で１１００℃以上の温度で焼鈍する。仕上げ焼鈍後、表面は既に平滑化されているので、張力コーティング処理、または、必要な前処理の後に、張力コーティング処理を行い、必要に応じて、レーザー照射等、あるいは、耐熱型の磁区制御を施せばよい。
【００３１】
【実施例】
〔実施例１〕
質量％で、Ｓｉ：３．３％、Ｍｎ：０．０７％、Ｃ：０．０７％、Ｓ：０．０２５％、酸可溶性Ａｌ：０．０３％、Ｎ：０．０１％、Ｓｎ：０．１％を含む板厚２．０ｍｍの熱延板を１１２０℃で２分間焼鈍し、その後、板厚０．２３ｍｍに冷延した。この冷延板を、窒素と水素の混合ガス中にて、酸化度（Ｐ_H2O／Ｐ_H2）を０．１４とし、脱炭焼鈍した。このときの焼鈍条件は、前段を均熱温度８２０℃で７５秒とし、後段の均熱温度を種々の温度で１５秒とした。この脱炭焼鈍板に、アルミナを主成分とする焼鈍分離剤を水スラリー状で塗布し、その後、仕上げ焼鈍を施した。仕上げ焼鈍は、１２００℃までは窒素１００％の雰囲気中で１５℃／ｈｒの昇温速度で行い、１２００℃で水素１００％に切り替え２０時間行った。
【００３２】
以上の工程により作製された鏡面材につき、水洗し、試料剪断の後、さらに、歪取り焼鈍を施し、ＳＳＴ法により磁束密度Ｂ₈を測定した。結果を表３に示す。
【００３３】
【表３】

【００３４】
前段の焼鈍の際に脱炭が進行したため、脱炭性に関しては、いずれの条件においても良好であった。さらに、後段の焼鈍温度を前段の温度よりも１０℃以上高くした試料２〜８においては、磁束密度Ｂ₈に関しても１．９３Ｔ以上であり、良好であった。試料９において磁束密度が低下した理由は、後段の温度が高すぎて一次再結晶粒径が粗大化し過ぎたため、良好な二次再結晶粒が得られなかったものと推定される。
【００３５】
〔実施例２〕
質量％で、Ｓｉ：３．３％、Ｍｎ：０．１％、Ｃ：０．０５％、Ｓ：０．００７％、酸可溶性Ａｌ：０．０３％、Ｎ：０．０１％、Ｓｎ：０．０５％を含む板厚２．０ｍｍの熱延板を１１００℃で２分間焼鈍した後、板厚０．２３ｍｍに冷延した。この冷延板を、窒素と水素の混合ガス中において、酸化度を種々変化させ脱炭焼鈍した。このときの焼鈍条件は、前段を均熱温度８２０℃で７０秒、後段を均熱温度８８０℃で２０秒とした。
【００３６】
さらに、アンモニア雰囲気中で焼鈍を行い、窒素量を０．０３％に増加してインヒビターの強化を行った。このときの脱炭焼鈍板の表面につき、赤外反射スペクトル測定を行い、鉄系酸化物の一種であるＦｅ₂ＳｉＯ₄のスペクトル（波数１０００／ｃｍ近傍）の有無を調査した。
この脱炭焼鈍板に、アルミナを主成分とする焼鈍分離剤を水スラリー状で塗布し、その後、仕上げ焼鈍を施した。仕上げ焼鈍は、１２００℃までは、窒素１００％の雰囲気中で１５℃／ｈｒの昇温速度で行い、１２００℃で水素１００％に切り替え２０時間行った。
【００３７】
以上の工程により作製された鏡面材につき、水洗し、試料剪断後、さらに、歪取り焼鈍を施し、そして、張力コーティングを形成した後、レーザー照射を行い、磁区を細分化し、ＳＳＴ法により磁束密度Ｂ₈及び鉄損Ｗ_17/50を測定した。結果を表４に示す。
【００３８】
【表４】

【００３９】
脱炭性に関しては、酸化度（Ｐ_H2O／Ｐ_H2）が０．０１以上である試料２〜４において良好である。このうち鉄損に関しては、酸化度０．２未満である試料２、３が０．７Ｗ／ｋｇ以下であり、非常に良好であった。試料４で鉄損不良である理由は、脱炭板において鉄系酸化物であるＦｅ₂ＳｉＯ₄が形成されるほど、過度に脱炭酸化量が増加し、その結果、仕上げ焼鈍後に鏡面度が著しく減退したためと推察される。
【００４０】
【発明の効果】
本発明は、脱炭焼鈍における脱炭性を良好に維持しつつ、磁気特性の良好な表面平滑度の高い鏡面方向性電磁鋼板を製造する手段を提示するものであり、その工業的な意義は極めて大きい。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing a grain-oriented electrical steel sheet that can improve iron loss characteristics by effectively finishing the surface in a method of manufacturing a grain-oriented electrical steel sheet mainly used as an iron core of a transformer. It is about.
[0002]
[Prior art]
The grain-oriented electrical steel sheet is a steel sheet containing about 2 to 4% of Si and highly accumulating the crystal grain orientation of the product steel plate in the {110} <001> orientation. As its magnetic characteristics, the magnetic flux density is high (represented by the magnetic flux density B ₈ value when a magnetic field of 800 A / m is applied), and the iron loss is low (magnetic flux density 1.7 T, energy loss of frequency 50 Hz). Although typified by) is in W _17/50 is required, in particular, recently, from the viewpoint of energy saving, there is an increasing demand to reduce the power loss. In response to this requirement, a technique for subdividing magnetic domains has been developed as means for reducing the iron loss of grain-oriented electrical steel sheets.
[0003]
In the case of a stacked iron core, a method for reducing the iron loss by subdividing the magnetic domain by irradiating the steel plate after the finish annealing with a laser beam to locally localize the strain is disclosed in, for example, Japanese Patent Application Laid-Open No. 58-26405. It is disclosed. In the case of a wound iron core, a method in which the effect of subdividing the magnetic domain does not disappear even if it is processed into an iron core and then subjected to stress release annealing is disclosed in, for example, Japanese Patent Laid-Open No. 62-8617. It is disclosed in the publication. By subdividing the magnetic domain using these technical means, the iron loss has been greatly reduced.
[0004]
However, by observing the movement of these magnetic domains, it has been found that there are also magnetic domains that do not move, and in order to further reduce the iron loss value of the grain-oriented electrical steel sheet, the glass film on the surface of the steel sheet is applied simultaneously with the magnetic domain fragmentation. We came to realize that it is important to eliminate the "pinning effect that inhibits the movement of magnetic domains".
In order to facilitate the magnetic domain movement as described above, it is effective not to form a glass film on the surface of the steel sheet. As a means for this, a method in which a glass film is not formed by using coarse high purity alumina as an annealing separator is disclosed in, for example, US Pat. No. 3,785,882. However, this method cannot eliminate inclusions directly under the surface, and the _margin for improving the iron loss is only 2% at most with W _15/60 .
[0005]
As a method of controlling the inclusions directly under the surface and achieving a mirror finish on the surface, a method of performing chemical polishing or electrolytic polishing after finish annealing is disclosed in, for example, Japanese Patent Application Laid-Open No. 64-83620. . However, methods such as chemical polishing and electropolishing are suitable for processing small samples of materials at the laboratory level, but performing this method on an industrial scale means controlling the concentration and temperature of chemicals, It is very difficult from the viewpoint of the problem of installation of pollution control equipment and the productivity.
[0006]
As a measure for solving this problem, a method in which the decarburization annealing step is performed in an atmosphere gas having an oxidation degree that does not form an Fe-based oxide and alumina is used as an annealing separator between the plates is disclosed in Japanese Patent Laid-Open No. 7-118749. Is disclosed.
However, it has been found that when carrying out this process industrially, it is difficult to obtain good magnetic properties while proceeding with decarburization stably.
[0007]
[Problems to be solved by the invention]
The present invention presents a means for producing a mirror-oriented electrical steel sheet having good surface properties and good magnetic properties while carrying out good decarburization in decarburization annealing.
[0008]
[Means for Solving the Problems]
The present invention is “mass%, Si: 2.0-4.0%, acid-soluble Al: 0.01-0.05%, N: 0.01% or less, Mn: 0.3% or less, S : 0.05% or less, remainder: Fe and inevitable impurities silicon steel hot-rolled steel strip is made into a steel plate of the final thickness by cold rolling at least once with intermediate annealing, and then decarburized annealing after, when stacking a steel plate, using alumina as a main component in the annealing separator between the plates, in the manufacturing method of oriented electrical steel sheet toward you annealing finishing the laminated steel sheet, said decarburization the annealing process is separated into front and rear stages, first and second stages of soaking temperature, T1 (° C.) and T2 a (° C.), respectively, 770 ≦ T1 ≦ 860, and the row physician in the range of T1 + 10 ≦ T2 ≦ 950 further, the oxidation degree of the previous atmospheric gas _{(P H2O / P H2),} 0.01 0.2 Not Production process ", the oriented electrical steel sheet towards you, characterized in that that the subject matter.
[0009]
Further, the present invention further in the manufacturing method of the preceding SL side oriented electrical steel sheet, after the decarburization annealing, and summarized in that the nitriding process until finish annealing. Further, the present invention further in the manufacturing method of the preceding SL side oriented electrical steel sheet, the decarburization annealing step, to be performed in an atmospheric gas of the oxidation degree is not formed of Fe-based oxides (P _H2O / P _H2) The gist.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
The inventors first performed the following tests in order to investigate the relationship between the decarburization annealing temperature, the decarburization property, and the magnetic flux density.
In a laboratory vacuum melting furnace, Si 3.3%, Mn 0.11%, C 0.05%, S 0.07%, acid-soluble Al 0.03%, N 0.01% in mass%. After producing the steel slab containing, it was heated at 1150 ° C. and then hot-rolled to obtain a hot-rolled sheet having a thickness of 2.0 mm. The hot-rolled sheet was annealed at 1100 ° C. for 2 minutes, then pickled, and further cold-rolled to a final sheet thickness of 0.23 mm.
[0012]
The cold-rolled sheet was decarburized and annealed at various temperatures for 90 seconds in a wet gas containing hydrogen and nitrogen (P _H2O / P _H2 = 0.13), and then steel in an ammonia-containing gas. The amount of medium nitrogen was increased to 0.02% to strengthen the inhibitor.
An annealing separator mainly composed of alumina was applied to the decarburized annealing plate in the form of a water slurry, and then finish annealing was performed. The final annealing was performed at a temperature increase rate of 15 ° C./hr in an atmosphere of 100% nitrogen up to 1200 ° C., and the annealing was performed for 20 hours by switching to 100% hydrogen at 1200 ° C.
[0013]
About the mirror surface material produced by the above process, after water washing and sample shearing, strain relief annealing was further performed, and magnetic measurement was performed by the SST method. Table 1 shows the amount of carbon after decarburization annealing and the value of magnetic flux density B ₈ after strain relief annealing.
[0014]
[Table 1]

[0015]
If the carbon content of the product plate exceeds 25 ppm, magnetic aging, that is, magnetic deterioration accompanying a change with time occurs, so the carbon content of the decarburized and annealed plate needs to be controlled to 25 ppm or less.
From Table 1, it can be seen that the temperature range in which the carbon content of the decarburized and annealed plate satisfies 25 ppm or less is 770 to 860 ° C. Outside this temperature range, that is, when the temperature is lower than 770 ° C., the carbon becomes diffusion-controlled, and it becomes impossible to move to the steel sheet surface in a short time, resulting in poor decarburization. On the other hand, when the temperature exceeds 860 ° C., the external A very dense SiO ₂ oxide layer having a form close to oxidation is formed on the surface of the steel sheet, and carbon cannot pass through the oxide layer, so that it is assumed that decarburization is poor.
[0016]
On the other hand, with respect to the magnetic flux density B ₈ , the higher the annealing temperature, the better, 1.90 T or higher at 830 ° C. or higher, and 1.94 T or higher at 870 ° C. or higher. As for the reason why the magnetic flux density is better when the annealing temperature is higher, the details are currently unknown, but it is considered as follows.
In other words, in the manufacturing process of the mirror-oriented electrical steel sheet of this time, in the decarburization annealing process, a somewhat dense SiO ₂ oxide layer is formed, and this oxide layer controls the inhibitor during the final annealing, and a good secondary Recrystallization is realized.
[0017]
When the decarburization annealing temperature is increased, the SiO ₂ oxide layer is formed more densely. This dense oxide layer has a favorable effect on preventing the weakening of the inhibitor during finish annealing. It is assumed that there is.
From the above, from the viewpoint of carbon content and magnetic flux density, considering the comprehensive optimum decarburization annealing temperature, 830 to 860 ° C. (samples 5 and 6) is appropriate from Table 1. However, in these samples, it cannot be said that the magnetic flux density is sufficiently high, and in that sense, it is difficult to ensure both decarburization and increase the magnetic flux density.
[0018]
Therefore, the present inventors have heretofore been difficult to realize by dividing the decarburization annealing soaking temperature into the former stage and the latter stage and separating the functions of promoting decarburization in the former stage and promoting increasing the magnetic flux density in the latter stage. Attempts were made to solve the above problems. The details will be described below.
The following tests were conducted using the cold-rolled sheets of the components and processes used in the above test. That is, the cold-rolled sheet, in a wet gas containing hydrogen and nitrogen _{(P H2O / P H2 = 0.13} ), first, in front of the decarburization annealing furnace were carried out 830 ° C., 75 seconds annealing. Subsequently, in the latter stage of the decarburization annealing furnace, various temperatures were changed, and annealing was performed for 15 seconds in the same atmosphere.
[0019]
Thereafter, the nitrogen content in the steel was increased to 0.02% in ammonia gas to strengthen the inhibitor. An annealing separator containing alumina as a main component was applied to the decarburized annealing plate as a water slurry, and then subjected to finish annealing. The final annealing was performed at a temperature increase rate of 15 ° C./hr in an atmosphere of 100% nitrogen up to 1200 ° C., and was switched to 100% hydrogen at 1200 ° C. and annealed for 20 hours.
[0020]
About the mirror surface material produced by the above process, after water washing and sample shearing, strain relief annealing was further performed, and magnetic measurement was performed by the SST method. Table 2 shows the amount of carbon after decarburization annealing and the value of magnetic flux density B ₈ after strain relief annealing.
[0021]
[Table 2]

[0022]
Since decarburization progressed before the decarburization annealing, the decarburization property was good under any conditions. Furthermore, in Samples 2 to 8 in which the annealing temperature in the latter stage of the decarburization annealing furnace was higher by 10 ° C. or more than the temperature in the preceding stage, the magnetic flux density B ₈ was also 1.93 T or more, which was good. The reason for the decrease in the magnetic flux density in Sample 9 is presumed that the subsequent stage temperature was too high, the primary recrystallized grain size was too coarse, and good secondary recrystallized grains were not obtained.
[0023]
From the above, the present inventors have newly found that it is possible to achieve both decarburization and high magnetic flux density, which have been difficult in the past, by functionally separating the decarburization annealing temperature into two stages, the former stage and the latter stage. The present invention has been completed.
Subsequently, an embodiment of the present invention will be described. As a basic production method, a production method using AlN and MnS by Taguchi, Sakakura, etc. as main inhibitors (for example, Japanese Patent Publication No. 40-15644), or (Al, Si) N by Komatsu, etc. as a main inhibitor. A production method to be used (for example, Japanese Patent Publication No. 62-45285) may be applied.
[0024]
Si is an important element for increasing electric resistance and reducing iron loss. When the content exceeds 4.0%, the material is easily cracked during cold rolling, and rolling becomes impossible. On the other hand, if the Si content is lowered, α → γ transformation occurs during finish annealing and the crystal directionality is impaired, so 2.0% which does not substantially affect the crystal directionality is made the lower limit.
Acid-soluble Al combines with N and is an element essential for functioning as an inhibitor as AlN or (Al, Si) N. The range of 0.01 to 0.05% at which the magnetic flux density is increased is set as the limited range. If N is present in an amount exceeding 0.01% during steelmaking, voids called blisters are generated in the steel sheet, so the upper limit is 0.01%.
[0025]
Regarding the amount of Mn and the amount of S, it is preferable to set Mn 0.3% or less and S0.05% or less from the viewpoint of securing an appropriate inhibitor amount for improving secondary recrystallization. As other inhibitor constituent elements, B, Bi, Se, Pb, Mo, Sb, Sn, Ti, V, or the like may be added.
The molten steel of the above components is formed into a hot-rolled sheet by a normal process, or a molten steel is continuously cast into a thin strip. The hot-rolled sheet or continuous cast ribbon is cold-rolled immediately or after being annealed for a short time. This short-time annealing is performed in a temperature range of 750 to 1200 ° C. for 30 seconds to 30 minutes, and is effective for enhancing the magnetic properties of the product. It is better to decide whether to accept or reject the product considering the desired property level and cost.
[0026]
Basically, the cold rolling may be performed at a final cold rolling reduction of 80% or more as disclosed in Japanese Patent Publication No. 40-15644.
In order to remove carbon contained in the steel sheet after cold rolling, decarburization annealing is performed in a wet hydrogen atmosphere. As shown in Example 1, in order to produce a specular grain-oriented electrical steel sheet, the degree of oxidation of decarburization annealing (P _H2O / P _H2 ) was decarburized and Fe-based oxide (Fe ₂ SiO ₄ , It is necessary to set the degree of oxidation not to generate FeO or the like, that is, 0.01 or more and less than 0.2.
[0027]
The decarburization annealing temperature, which is the main point of the present invention, is divided into a first stage (soaking temperature T1 (° C.)) and a latter stage (soaking temperature T2 (° C.)), and 770 ≦ T1 ≦ 860 and T1 + 10 ≦ T2 ≦, respectively. It needs to be in the range of 950. This is because when T1 is outside this range, decarburization failure occurs, and when T2 is outside the above range, a high magnetic flux density cannot be obtained on the product plate. Within this range, more preferable ranges are 800 ≦ T1 ≦ 850 and T1 + 20 ≦ T2 ≦ 930.
[0028]
About pre-stage annealing in decarburization annealing, in order to advance decarburization, it is preferred to hold for 30 seconds or more. Further, regarding the subsequent annealing, it is preferable to hold for 3 seconds or more in order to improve the magnetic flux density.
[0029]
In the manufacturing method (for example, Japanese Patent Publication No. Sho 62-45285) using (Al, Si) N as the main inhibitor for the decarburized annealing plate, nitriding treatment is performed. The nitriding method is not particularly limited, and a method of passing the strip through an atmospheric gas having nitriding ability such as ammonia can be employed. The amount of nitriding is 0.005% or more, preferably, the total nitrogen amount is nitrided by Al equivalent or more in steel.
[0030]
When laminating these decarburized annealed plates, alumina as an annealing separator is dry-coated by a water slurry method, an electrostatic coating method, or the like. The laminated plate is subjected to finish annealing, and secondary recrystallization and nitride purification are performed.
Performing secondary recrystallization in a predetermined temperature range by means such as holding at a constant temperature as disclosed in JP-A-2-258929 is effective in increasing the magnetic flux density. After the secondary recrystallization is completed, annealing is performed at a temperature of 1100 ° C. or higher in a 100% hydrogen atmosphere in order to purify the nitride and smooth the surface. After finish annealing, the surface has already been smoothed, so tension coating treatment or necessary pretreatment is followed by tension coating treatment, and if necessary, laser irradiation, etc. or heat-resistant magnetic domain control. Just give it.
[0031]
【Example】
[Example 1]
In mass%, Si: 3.3%, Mn: 0.07%, C: 0.07%, S: 0.025%, acid-soluble Al: 0.03%, N: 0.01%, Sn: A hot-rolled sheet having a thickness of 2.0 mm containing 0.1% was annealed at 1120 ° C. for 2 minutes, and then cold-rolled to a thickness of 0.23 mm. The cold-rolled sheet was decarburized and annealed in a mixed gas of nitrogen and hydrogen with an oxidation degree (P _H2O / P _H2 ) of 0.14. The annealing conditions at this time were such that the former stage had a soaking temperature of 820 ° C. for 75 seconds, and the latter stage had a soaking temperature of 15 seconds at various temperatures. An annealing separator mainly composed of alumina was applied to the decarburized annealing plate in the form of a water slurry, and then finish annealing was performed. The final annealing was performed at a temperature increase rate of 15 ° C./hr in an atmosphere of 100% nitrogen up to 1200 ° C., and switched to 100% hydrogen at 1200 ° C. for 20 hours.
[0032]
The mirror surface material produced by the above steps was washed with water, subjected to sample shearing, further subjected to strain relief annealing, and the magnetic flux density B ₈ was measured by the SST method. The results are shown in Table 3.
[0033]
[Table 3]

[0034]
Since decarburization progressed during the previous annealing, the decarburization property was good under any conditions. Further, in Samples 2 to 8 in which the annealing temperature in the subsequent stage was higher by 10 ° C. or more than the temperature in the previous stage, the magnetic flux density B ₈ was also 1.93 T or more, which was favorable. It is estimated that the reason why the magnetic flux density decreased in Sample 9 was that good secondary recrystallized grains could not be obtained because the temperature at the latter stage was too high and the primary recrystallized grain size was too coarse.
[0035]
[Example 2]
In mass%, Si: 3.3%, Mn: 0.1%, C: 0.05%, S: 0.007%, acid-soluble Al: 0.03%, N: 0.01%, Sn: A hot-rolled sheet having a thickness of 2.0 mm containing 0.05% was annealed at 1100 ° C. for 2 minutes, and then cold-rolled to a thickness of 0.23 mm. The cold-rolled sheet was decarburized and annealed with various degrees of oxidation in a mixed gas of nitrogen and hydrogen. The annealing conditions at this time were such that the former stage was a soaking temperature of 820 ° C. for 70 seconds and the latter stage was a soaking temperature of 880 ° C. for 20 seconds.
[0036]
Furthermore, annealing was performed in an ammonia atmosphere, and the amount of nitrogen was increased to 0.03% to strengthen the inhibitor. Infrared reflection spectrum measurement was performed on the surface of the decarburized and annealed plate at this time, and the presence or absence of a spectrum (near wave number 1000 / cm) of Fe ₂ SiO ₄ which is a kind of iron-based oxide was investigated.
An annealing separator mainly composed of alumina was applied to the decarburized annealing plate in the form of a water slurry, and then finish annealing was performed. The final annealing was performed at a temperature increase rate of 15 ° C./hr in an atmosphere of 100% nitrogen up to 1200 ° C. and switched to 100% hydrogen at 1200 ° C. for 20 hours.
[0037]
The mirror material produced by the above steps is washed with water, subjected to sample shearing, further subjected to strain relief annealing, and after forming a tension coating, laser irradiation is performed to subdivide the magnetic domain, and the magnetic flux density is measured by the SST method. B ₈ and iron loss W _17/50 were measured. The results are shown in Table 4.
[0038]
[Table 4]

[0039]
As for decarburization, samples 2 to 4 having an oxidation degree (P _H2O / P _H2 ) of 0.01 or more are good. Of these, regarding iron loss, Samples 2 and 3 having an oxidation degree of less than 0.2 were 0.7 W / kg or less, which was very good. Why the sample 4 is a core loss failure, as Fe ₂ SiO ₄ is an iron-based oxide is formed in the decarburization plate, excessive decarboxylation volume increases, as a result, the specularity after finish annealing This is probably due to a significant decline.
[0040]
【The invention's effect】
The present invention provides a means for producing a mirror-oriented electrical steel sheet with good surface properties and good magnetic properties while maintaining good decarburization in decarburization annealing, and its industrial significance is Very large.

Claims (3)

In mass%, Si: 2.0 to 4.0%, acid-soluble Al: 0.01 to 0.05%, N: 0.01% or less, Mn: 0.3% or less, S: 0.05% Hereinafter, the remainder: the silicon steel hot-rolled steel strip composed of Fe and inevitable impurities, the steel sheet of the final plate thickness by one or more cold rolling sandwiching the intermediate annealing, and then after decarburization annealing, when stacking a steel plate, using alumina as a main component in the annealing separator between the plates, in the manufacturing method of oriented electrical steel sheet toward you annealing finishing the laminated steel sheet, front the decarburization annealing step separated downstream and, upstream and downstream of the soaking temperature, T1 (° C.) and T2 (° C.) and, respectively, are performed by the following ranges, further, the oxidation degree of the pre-stage of the atmospheric gas (P _H2O / P _H2) the method for producing a oriented electrical steel sheet towards you, characterized in that less than 0.01 to 0.2.
770 ≦ T1 ≦ 860
T1 + 10 ≦ T2 ≦ 950 Wherein after the decarburization annealing, manufacturing method of oriented electrical steel sheet towards the claim 1, wherein the performing the nitriding process until finish annealing. Wherein the step of decarburization annealing, manufacturing method of oriented electrical steel sheet towards the claim 1 or 2, wherein the performing by the degree of oxidation without formation of Fe-based oxides (P _H2O / P _H2) ambient gas.