JP2024094075A - Grain-oriented electrical steel sheet and its manufacturing method - Google Patents

Abstract

【課題】昨今の環境規制への機運の高まりや、エネルギー問題、カーボンニュートラルなどの影響を受け、変圧器の損失を一層抑えるために、さらなる低鉄損化を達成できる方向性電磁鋼板を提供する。【解決手段】所定の成分組成とし、所定の範囲の全ての粒界近傍部に対し、結晶方位がゴス方位から１０度以上ずれている結晶粒が面積率にして２０％以下（０％含む）の割合となる粒界近傍部を５０％以上とする。【選択図】図１[Problem] To provide a grain-oriented electrical steel sheet capable of achieving even lower iron loss in order to further suppress losses in transformers in light of the recent growing momentum toward environmental regulations, energy issues, carbon neutrality, etc. [Solution] With a specified composition, the grain boundary vicinity portion within a specified range has an area ratio of 20% or less (including 0%) of crystal grains whose crystal orientation deviates from the Goss orientation by 10 degrees or more, and is 50% or more. [Selected Figure] Figure 1

Description

本発明は、鉄損が少ない方向性電磁鋼板およびその製造方法に関する。 The present invention relates to grain-oriented electrical steel sheets with low iron loss and a method for manufacturing the same.

方向性電磁鋼板は、Ｓｉを質量％で７％以下含有し、鉄の磁化容易軸である＜００１＞が鋼板の圧延方向に対し、高度に集積した組織を有する材料であり、主として変圧器鉄心材料として用いられている。 Grain-oriented electrical steel sheet contains 7% or less Si by mass and has a structure in which the magnetization easy axis of iron, <001>, is highly concentrated in the rolling direction of the steel sheet, and is primarily used as a transformer core material.

変圧器に最も求められる特性の一つとして、低損失であることが挙げられるが、変圧器の損失の大部分は、鉄心に生じる鉄損が占めている。よって、鉄心材料である方向性電磁鋼板の低鉄損化は変圧器の特性向上に極めて重要である。 One of the most important characteristics required for a transformer is low loss, but the majority of losses in a transformer are due to iron loss that occurs in the iron core. Therefore, reducing iron loss in the grain-oriented electrical steel sheet that is the iron core material is extremely important for improving the characteristics of a transformer.

昨今のエネルギー規制に伴い、低損失な変圧器を作製可能にする低鉄損な方向性電磁鋼板の開発は年々強く求められてきている。 Due to recent energy regulations, there is a growing demand each year for the development of low-core-loss grain-oriented electrical steel sheets that enable the creation of low-loss transformers.

そこで、低鉄損な方向性電磁鋼板を開発するにあたり、組織の方位先鋭化、高張力被膜の付与、鋼板表面への不均一性の導入による磁区細分化技術の開発などが進められてきた。 Therefore, in order to develop grain-oriented electrical steel sheets with low iron loss, efforts have been made to sharpen the orientation of the structure, apply high-tensile coatings, and develop magnetic domain refining technologies by introducing non-uniformity into the steel sheet surface.

例えば、特許文献１は、方向性電磁鋼板の製造の際に、二次再結晶焼鈍の均熱パターンとその雰囲気を制御することによって、高度に集積された集合組織を作りこみ、低鉄損化を達成する技術について記されている。 For example, Patent Document 1 describes a technology that creates a highly concentrated texture and achieves low iron loss by controlling the soaking pattern and atmosphere of secondary recrystallization annealing during the production of grain-oriented electrical steel sheets.

また、特許文献２は、被膜形成に用いられる材料の熱膨張係数を調整することにより、大きな被膜張力を得ることで優れた磁気特性を発現させる技術について記されている。 Furthermore, Patent Document 2 describes a technology that achieves excellent magnetic properties by adjusting the thermal expansion coefficient of the material used to form the coating, thereby obtaining a large coating tension.

さらに、特許文献３では、方向性電磁鋼板の絶縁被膜を局所的に除き、電解エッチングを施し、溝を掘るという磁区細分化処理を施すことで、低鉄損化を達成している。 Furthermore, in Patent Document 3, low iron loss is achieved by locally removing the insulating coating of the grain-oriented electrical steel sheet, performing electrolytic etching, and performing a magnetic domain refining process in which grooves are dug.

特開２０２０－７６３７号公報JP 2020-7637 A 特開２０２０－１９６９５４号公報JP 2020-196954 A 特開平２－５０９１８号公報Japanese Patent Application Laid-Open No. 2-50918 特公昭５４－２３６４７号公報Japanese Patent Publication No. 54-23647

前述の特許文献１～３に記載されたように、さまざまな方法でその鉄心材料の方向性電磁鋼板の鉄損を抑制する技術が開発されている。 As described in the above-mentioned Patent Documents 1 to 3, various methods have been developed to reduce the iron loss of the grain-oriented electromagnetic steel sheet that is used as the core material.

しかしながら、近年では、昨今の環境規制への機運の高まりや、エネルギー問題、カーボンニュートラルなどの影響を受け、変圧器の損失をさらに抑えることが求められている。 However, in recent years, due to the growing momentum towards environmental regulations, energy issues, carbon neutrality, etc., there is a demand to further reduce transformer losses.

本発明は、上記の事情を鑑みてなされたものであって、前記課題のためにさらなる低鉄損化を達成できる方向性電磁鋼板を提供することを目的とする。 The present invention was made in consideration of the above circumstances, and aims to provide a grain-oriented electrical steel sheet that can achieve even lower iron loss to solve the above problems.

方向性電磁鋼板を低鉄損化するための手段は多岐にわたるが、発明者らは、特に磁区細分化の手段に注目した。すなわち、新規な磁区細分化の手法を検討した。 There are many different ways to reduce iron loss in grain-oriented electrical steel sheets, but the inventors focused in particular on methods for refining magnetic domains. In other words, they investigated new methods for refining magnetic domains.

ここで、方向性電磁鋼板における磁区細分化とは、鋼板表面に発生する磁極量を増加させることで、大きくなった静磁エネルギーを緩和するために圧延方向を向いた１８０°磁区を細分化することである。 Here, magnetic domain refinement in grain-oriented electrical steel sheet refers to the refinement of 180° magnetic domains oriented in the rolling direction in order to reduce the increased magnetostatic energy by increasing the amount of magnetic poles generated on the steel sheet surface.

そのための方法として、例えば、突起ロールによる溝形成や、鋼板表面へのレーザー照射による熱歪を導入する方法が開発されている。これらの技術はいずれも既存の製品板、製品コイルに加工を実施することで磁区細分化処理を施すものであり、その母材は通常の方向性電磁鋼板が用いられている。 Methods that have been developed for this purpose include, for example, forming grooves using protruding rolls and introducing thermal distortion by irradiating the steel sheet surface with a laser. Both of these technologies involve processing existing product sheets and product coils to perform magnetic domain refinement, and the base material used is ordinary grain-oriented electrical steel sheet.

発明者らは、かかる母材である方向性電磁鋼板の磁区を細分化するために、まず、二次再結晶粒の粒径を人為的に小さくすることを目指した。これは、母材自体を磁区細分化材とすることで、それ自体が低鉄損の方向性電磁鋼板になるとともに、溝形成や熱歪による磁区細分化処理を施すことで、さらなる低鉄損化が期待できるからである。加えて、母材の二次再結晶粒を小さくすると、結晶粒界が増えるので、結晶粒間に生じる磁極の量が増加し磁区細分化効果が期待できるからである。 In order to subdivide the magnetic domains of the parent material, grain-oriented electrical steel sheet, the inventors first aimed to artificially reduce the grain size of the secondary recrystallized grains. This is because by making the parent material itself a magnetic domain refinement material, it becomes a grain-oriented electrical steel sheet with low iron loss, and by carrying out magnetic domain refinement processing by groove formation or thermal distortion, further reduction in iron loss can be expected. In addition, by making the secondary recrystallized grains of the parent material smaller, the number of crystal grain boundaries increases, which increases the amount of magnetic poles generated between the crystal grains, and a magnetic domain refinement effect can be expected.

ここで、特許文献４には、鋼板への塑性加工、熱加工、化学的加工によって鋼板表面に局所的に二次再結晶の粒成長の阻害領域を導入することで、その領域に沿って二次再結晶粒を成長させ、結晶粒を小径化するという技術が開示されている。 Patent Document 4 discloses a technique in which a region that inhibits the grain growth of secondary recrystallization is introduced locally on the surface of the steel sheet by plastic processing, thermal processing, and chemical processing, and secondary recrystallized grains are allowed to grow along that region, thereby reducing the diameter of the crystal grains.

また、特許文献４には、この技術に関し、最終焼鈍前に、鋼板に対し機械的に導入した歪みによって、最終焼鈍中に異常粒成長部分を形成し、この部分が二次再結晶をせき止め、二次再結晶粒を小さいものに仕上げ、鉄損が改善されると開示されている。 Patent Document 4 also discloses that, with regard to this technology, mechanically introducing strain into the steel sheet before final annealing forms areas of abnormal grain growth during final annealing, and these areas block secondary recrystallization, resulting in smaller secondary recrystallized grains and improving iron loss.

発明者らは、実際に特許文献４に記載の方法に従い、サンプルを作製した。すなわち、最終焼鈍前の鋼板表面に歪みを入れた後に、最終焼鈍にて製品板に仕上げ、かかる製品板の鉄損を調べた。すると、鉄損が比較的良いサンプルが得られたものの、一部、鉄損の大きいサンプルが認められた。 The inventors actually prepared samples according to the method described in Patent Document 4. That is, they introduced strain into the surface of the steel sheet before final annealing, and then finished the steel sheet into a product sheet by final annealing, and investigated the iron loss of the product sheet. As a result, although samples with relatively good iron loss were obtained, some samples with large iron loss were also found.

そこで、これらのサンプルの圧延方向に沿った断面を詳細に調査すると、歪み導入箇所の直下に導入された二次再結晶粒の粒界付近に微細粒が多数形成されていることが分かった。
そして、鉄損が比較的良いサンプルについては歪み部直下の二次再結晶粒の粒界が多い一方で、鉄損が悪いサンプルについては、前記微細粒の析出量が減少してはいるものの多数析出していた。この微細粒は最終焼鈍中に成長する二次再結晶ではなく、歪みが導入されることで、最終焼鈍での昇温中に粗大化し、二次再結晶粒に蚕食されなかった結晶粒（結晶方位がゴス方位から１０度以上ずれている結晶粒）であり、ゴス粒ではないことから、この結晶粒（微細粒）が存在することで鉄損を低下させていたと推定される。 Therefore, when the cross sections of these samples along the rolling direction were examined in detail, it was found that a large number of fine grains were formed near the grain boundaries of secondary recrystallized grains introduced immediately below the strain-introduced location.
In the samples with relatively good iron loss, there were many grain boundaries of secondary recrystallized grains directly below the strained portion, whereas in the samples with poor iron loss, the fine grains precipitated in large numbers, although the amount of precipitation had decreased. These fine grains were not secondary recrystallized grains that grew during final annealing, but were crystal grains (crystal grains whose crystal orientation was shifted by 10 degrees or more from the Goss orientation) that had become coarse during the temperature rise in final annealing due to the introduction of strain and had not been eaten away by the secondary recrystallized grains, and since they were not Goss grains, it is presumed that the presence of these crystal grains (fine grains) reduced the iron loss.

さらに、発明者らは、特許文献４に開示されている方法をもとに、以下の実験［１］を考えた。
すなわち、最終焼鈍後の歪み導入箇所の直下への微細粒の発生を抑制することで、人工的な二次再結晶粒の粒界を導入し、二次再結晶粒を小径化することによる鉄損低減の効果を、前記特許文献４に記載の技術を超えて高める方法を模索するために、以下の実験［１］を実施した。 Furthermore, the inventors devised the following experiment [1] based on the method disclosed in Patent Document 4.
That is, the following experiment [1] was carried out in order to explore a method for enhancing the effect of reducing iron loss by suppressing the generation of fine grains immediately below the strain-introduced portion after final annealing, thereby introducing artificial grain boundaries of secondary recrystallized grains and reducing the diameter of the secondary recrystallized grains, beyond the effect of the technique described in Patent Document 4.

実験［１］
脱炭焼鈍を施した０．２３ｍｍ厚の方向性電磁鋼板の脱炭焼鈍板に対し、かかる脱炭焼鋼板の圧延方向に対し直角に、かつ幅方向全体に均一に圧下されるように、突起が付与されたロールへの荷重圧力を変え、周期的な歪みおよび溝を導入した。このロールの外周部の円周は２ｍであり、突起間隔は全て等しく、１０ｍｍであった。また、比較用として、歪みを導入しないプレーン条件のサンプルも作製した。 Experiment [1]
The load pressure on the roll with protrusions was changed so that the decarburized annealed sheet of 0.23 mm thick grain-oriented electrical steel sheet was pressed down perpendicular to the rolling direction of the decarburized steel sheet and uniformly across the width, thereby introducing periodic distortion and grooves. The circumference of the outer periphery of this roll was 2 m, and the protrusion intervals were all equal, 10 mm. For comparison, a sample was also prepared under plain conditions in which no distortion was introduced.

次いで、酸化マグネシウムを主成分とする焼鈍分離剤を塗布した後、最終焼鈍を１２００℃の保定温度で実施することで、二次再結晶およびフォルステライト被膜の形成をさせた。 Next, an annealing separator containing magnesium oxide as its main component was applied, and final annealing was performed at a holding temperature of 1200°C to cause secondary recrystallization and the formation of a forsterite film.

かように作製した製品板を、圧延方向に２８０ｍｍ、圧延直交方向に３０ｍｍの長さに剪断後、励磁周波数：５０Ｈｚ、励磁磁束密度：１．７ＴでＪＩＳ Ｃ ２５５０－１：２０１１に基づきエプスタイン試験を実施し、鉄損を測定した。 The product plate thus produced was sheared to a length of 280 mm in the rolling direction and 30 mm in the direction perpendicular to the rolling direction, and then an Epstein test was carried out based on JIS C 2550-1:2011 with an excitation frequency of 50 Hz and an excitation magnetic flux density of 1.7 T to measure the iron loss.

鉄損測定後のサンプルの圧延方向における、板厚方向の鋼板断面観察を実施した。観察箇所は、図１に示すように、かかる鋼板断面の二次再結晶粒の粒界の圧延方向長さのうち最大長さの中心である粒界位置から圧延方向に沿って、±５ｍｍの範囲とした（本発明において、「粒界近傍部」という）。かかる範囲内において、ゴス方位から１０°以上ずれた結晶粒（微細粒）の観察面積に対する面積率を計算した。上記粒界位置を、図１、図２、図３および図４に示す各結晶粒の配置の例に則り示している。
なお、本発明で歪導入箇所とは、鋼板表面に歪を与えた部分のうち、鋼板圧延方向に対する中心部を指し、今回のような突起ロールであれば、突起が鋼板と接した部分の圧延方向中心部を指す。 After the iron loss measurement, the steel sheet cross section was observed in the thickness direction in the rolling direction of the sample. The observation area was within a range of ±5 mm along the rolling direction from the grain boundary position, which is the center of the maximum length of the grain boundary of the secondary recrystallized grain in the rolling direction of the steel sheet cross section, as shown in Figure 1 (referred to as "grain boundary vicinity" in the present invention). Within this range, the area ratio of crystal grains (fine grains) deviated by 10° or more from the Goss orientation to the observed area was calculated. The above grain boundary positions are shown in accordance with the examples of the arrangement of each crystal grain shown in Figures 1, 2, 3, and 4.
In the present invention, the strain introduction location refers to the center in the rolling direction of the steel sheet among the parts where strain is applied to the steel sheet surface, and in the case of a protruding roll as used in this embodiment, refers to the center in the rolling direction of the part where the protrusions contact the steel sheet.

図１に記載のように、二次再結晶粒の粒界が鋼板の圧延面の表面と裏面に貫通して導入されている二次再結晶粒の粒界に微細粒が隣り合うように析出している場合は、二次再結晶粒と微細粒との間に形成される粒界が表面に露出した位置をＡ、Ｂ、Ｃとする。
このとき、鋼板の反対の面にあるＣをＡ、Ｂ側の面に垂直投射したときの点をＣ´として、かかるＣ´と上記Ａ、Ｂとの距離、すなわち二次再結晶粒の粒界の圧延方向長さとなるＡＣ´とＢＣ´の長さを比較する。すると、図１の場合は、ＡＣ´＞ＢＣ´であることから、最も距離が大きくなる、すなわち最大長さとなる組み合わせはＡとＣ´となる。そこで、Ｃ´の基の点ＣとＡとを結んだＡＣを採用し、かかるＡＣの圧延方向に対する中心を、本発明では、粒界位置と定義している。 As shown in FIG. 1 , in the case where fine grains are precipitated so as to be adjacent to the grain boundaries of secondary recrystallized grains that have been introduced penetrating through to the front and back surfaces of the rolled surface of the steel sheet, the positions where the grain boundaries formed between the secondary recrystallized grains and the fine grains are exposed on the surface are designated as A, B, and C.
At this time, point C' is defined as a point obtained by vertically projecting C on the opposite surface of the steel sheet onto the surfaces on the A and B sides, and the distance between this C' and the above-mentioned A and B, that is, the lengths AC' and BC', which are the rolling direction lengths of the grain boundaries of secondary recrystallized grains, are compared. In the case of Fig. 1, AC'>BC', so the combination with the longest distance, i.e., the maximum length, is A and C'. Therefore, AC connecting the base point C and A of C' is adopted, and the center of this AC in the rolling direction is defined as the grain boundary position in the present invention.

また、図２に記載のように、二次再結晶粒の粒界に隣接する微細粒がない場合は、その二次再結晶粒の粒界が鋼板表面に露出しているＡ点とＢ点とを結んだ粒界ＡＢの圧延方向に対する中心を粒界位置と定義した。 In addition, as shown in Figure 2, when there are no fine grains adjacent to the grain boundary of a secondary recrystallized grain, the center in the rolling direction of the grain boundary AB connecting points A and B where the grain boundary of the secondary recrystallized grain is exposed on the steel sheet surface is defined as the grain boundary position.

さらに、図３に記載のように、二次再結晶粒の厚さ方向の中間でお互いが接するように複数の微細粒が析出したり、図４に記載のように、二次再結晶粒を微細粒が左右に分断したりしているときは、二次再結晶粒と微細粒の間のそれぞれの粒界が鋼板表面に露出している点、Ａ，Ｂ，Ｃ，Ｄ点を取る。次いで、図３および図４に示したように、鋼板の反対の面にあるＣおよびＤをＡ、Ｂ側の面に垂直投射したときの点をそれぞれＣ´およびＤ´とし、距離ＡＣ´，ＡＤ´，ＢＣ´およびＢＤ´を考える。
そして、その中で最も距離が大きくなる組み合わせを求め、その組み合わせの鋼板表面に露出している点と投射前の鋼板表面に露出している点とを結んだ線の圧延方向に対する中心を粒界位置と定義した。 Furthermore, when a plurality of fine grains are precipitated so as to be in contact with each other at the middle of the thickness direction of the secondary recrystallized grain as shown in Fig. 3, or when a fine grain divides the secondary recrystallized grain into left and right as shown in Fig. 4, points A, B, C, and D are taken as the points at which the grain boundaries between the secondary recrystallized grains and the fine grains are exposed on the steel sheet surface. Next, as shown in Fig. 3 and Fig. 4, points C' and D' are taken as the points when C and D on the opposite surface of the steel sheet are vertically projected onto the surfaces on the A and B sides, respectively, and distances AC', AD', BC', and BD' are considered.
Then, the combination with the greatest distance was determined, and the center in the rolling direction of the line connecting the point exposed on the steel sheet surface of that combination and the point exposed on the steel sheet surface before projection was defined as the grain boundary position.

すなわち、図３および図４では、いずれもＡＤ´が最も長いため、Ａと、Ｄ´の投射前の点Ｄとを結んだ線ＡＤを採用し、かかるＡＤの圧延方向に対する中心が粒界位置となる。 In other words, in both Figures 3 and 4, AD' is the longest, so the line AD connecting A and point D before the projection of D' is used, and the center of this AD in the rolling direction is the grain boundary position.

前記粒界近傍部（粒界位置から圧延方向に沿って、±５ｍｍの範囲）内における前記微細粒の面積率を計算した。かかる面積率の計算は、前記エプスタイン試験片を板幅方向の中央部で圧延方向に剪断した際の面積率をそのサンプルの面積率とし、１条件に付き、１０枚のエプスタイン試験片に対し、前記面積率を算出し、それら１０枚の平均面積率をその条件での面積率とした。
なお、かかる面積率は、歪を幅方向全体に均一に付与したので、板幅方向の中央部で取得可能である。ロールの当たり方が悪く、歪が幅方向全体に付与されていない場合は、最も多く導入された歪を横切ることができる板幅方向の位置で算出した。また、前記粒界位置の周期性は、ある歪とそれに隣接する歪の間隔を歪を付与する設備の１単位当たりの長さの二倍の長さに渡って測定し、繰り返し単位を調査することで取得可能である。
例えば、本例のような突起が付与されたロールでは、ロールの外周の円周の２倍の長さを測定し、周期性について評価した。 The area ratio of the fine grains in the vicinity of the grain boundary (within a range of ±5 mm from the grain boundary position along the rolling direction) was calculated. In calculating the area ratio, the area ratio of the Epstein test piece when it was sheared in the rolling direction at the center in the sheet width direction was defined as the area ratio of the sample, and the area ratio was calculated for 10 Epstein test pieces per condition, and the average area ratio of the 10 pieces was defined as the area ratio under that condition.
The area ratio can be obtained at the center of the sheet width direction because the strain was applied uniformly across the entire width direction. When the roll contact was poor and the strain was not applied across the entire width direction, the area ratio was calculated at the position in the sheet width direction that could cross the most introduced strain. The periodicity of the grain boundary positions can be obtained by measuring the interval between a certain strain and its adjacent strain over a length twice the length per unit of the equipment that applies the strain, and investigating the repeating unit.
For example, in the case of a roll having protrusions as in this example, the length twice the circumference of the outer periphery of the roll was measured and the periodicity was evaluated.

微細粒を判断するための結晶方位は、前記観察範囲内をＸ線回折法または電子線後方散乱回折法（ＥＢＳＤ）により測定することができる。Ｘ線及び電子線の試料からの反射角等が結晶方位ごとに異なるため、ランダム方位試料を基準とし、この反射強度等で結晶方位強度を求めることができる。 The crystal orientation for determining fine grains can be measured within the observation range by X-ray diffraction or electron backscatter diffraction (EBSD). Since the reflection angle of X-rays and electron beams from the sample differs for each crystal orientation, a random orientation sample is used as the standard, and the crystal orientation intensity can be determined from the reflection intensity, etc.

また、静磁状態の主磁区幅も測定した。主磁区幅は、前記断面観察を行った１０枚のエプスタイン試験片に対し、断面観察のために幅方向中心部から剪断する前に、圧延面に生じる主磁区を磁性コロイド粒子によるマグネットビューアーで出力する処理を施し、マイクロスコープで観察することで算出した。 The width of the main magnetic domain in the static magnetized state was also measured. The 10 Epstein test pieces that had been subjected to the cross-sectional observation were subjected to a process in which the main magnetic domains generated on the rolled surface were output using a magnet viewer made of magnetic colloid particles before being sheared from the center in the width direction for cross-sectional observation, and the main magnetic domain width was calculated by observing the main magnetic domains under a microscope.

この処理を鋼板全体に実施し、全ての主磁区幅を平均することで、そのサンプル１枚の主磁区幅とし、これを１０枚分平均することで、その実験条件での主軸区幅とした。
実験［１］の結果を表１に示す。なお、表１における存在比率とは、鋼板表面の単位面積（１ｍ^２）中の鋼板全厚に亘り含まれる前記粒界近傍部において、すべての粒界近傍部に対する微細粒面積率が２０％以下（０％含む）である粒界近傍部の存在数の比率を示している。ここでいう「存在数の比率」は、長さ比率に相当する。 This process was carried out on the entire steel sheet, and all the main domain widths were averaged to obtain the main domain width for that one sample. This was then averaged for 10 samples to obtain the main domain width under those experimental conditions.
The results of experiment [1] are shown in Table 1. The abundance ratio in Table 1 refers to the ratio of the number of grain boundary vicinity parts in which the fine grain area ratio is 20% or less (including ⁰ %) relative to all grain boundary vicinity parts, in the grain boundary vicinity parts contained throughout the entire thickness of the steel sheet in a unit area (1 m2) of the steel sheet surface. The "abundance ratio" here corresponds to the length ratio.

脱炭焼鈍板への突起が付与されたロールによる荷重が変化し、鋼板表面にある特定の範囲の圧下率が付与されると鉄損がさらに改善されることが分かった。この時、断面観察によって得られた微細粒の面積率が低下しており、鉄損が特に改善されるのは微細粒の面積率が２０％以下となっている粒界近傍部の存在数の比率が５０％以上のときであった。 It was found that when the load applied by the roll with protrusions to the decarburized annealed sheet is changed and a certain range of rolling reduction is applied to the steel sheet surface, iron loss is further improved. At this time, the area ratio of fine grains obtained by cross-sectional observation is reduced, and iron loss is particularly improved when the ratio of the number of grains near the grain boundaries where the area ratio of fine grains is 20% or less is 50% or more.

前記実験［１］により、発明者らは、歪みを導入し、周期的な二次再結晶粒の粒界を持たせた方向性電磁鋼板の磁区をより細分化し、さらなる低鉄損化が実現できることを知見した。 Through the above experiment [1], the inventors discovered that by introducing strain, the magnetic domains of grain-oriented electrical steel sheets with periodic secondary recrystallized grain boundaries can be further subdivided, thereby achieving even lower iron loss.

前記実験［１］により、鉄損が特に改善されるのは微細粒の面積率が２０％以下となっている粒界近傍部の存在数の比率が５０％以上のときというのが知見されたので、発明者らは、さらに微細粒を抑えるための手段を以下の実験［２］によって検討した。 The above experiment [1] revealed that iron loss is particularly improved when the ratio of the number of grains near the grain boundaries where the area ratio of fine grains is 20% or less is 50% or more. Therefore, the inventors investigated a means to further suppress fine grains in the following experiment [2].

実験［２］
脱炭焼鈍後の方向性電磁鋼板である厚さ：０．２３ｍｍの脱炭焼鈍板を、幅：３０ｍｍ、長さ：２８０ｍｍに剪断後、突起間隔：１０ｍｍの突起ロールで鋼板の幅方向に圧下率が２．０％になる荷重で歪みを導入した。次いで、焼鈍分離剤を塗布し１２００℃での最終焼鈍を実施した。この時、二次再結晶が開始される温度である８００℃までの昇温速度を毎時１℃、毎時３℃、毎時５℃、毎時１０℃に変更した。
最終焼鈍後の製品板の鉄損および微細粒の面積率および存在比率を、前記実験［１］と同様の方法で求めた。
実験［２］の結果を表２に示す。 Experiment [2]
The decarburized annealed sheet having a thickness of 0.23 mm, which is the grain-oriented electrical steel sheet after the decarburization annealing, was sheared to a width of 30 mm and a length of 280 mm, and then strain was introduced in the width direction of the steel sheet with a load that resulted in a rolling reduction of 2.0% using a protrusion roll with a protrusion interval of 10 mm. Next, an annealing separator was applied, and final annealing was performed at 1200°C. At this time, the heating rate up to 800°C, the temperature at which secondary recrystallization begins, was changed to 1°C per hour, 3°C per hour, 5°C per hour, and 10°C per hour.
The iron loss and the area ratio and abundance ratio of fine grains of the product sheet after final annealing were determined in the same manner as in the above-mentioned experiment [1].
The results of experiment [2] are shown in Table 2.

表２に示した実験［２］の結果より、昇温速度が毎時５℃以上の比較的速い条件で微細粒を有する粒界近傍部の発生を抑制できることが分かった。
すなわち、微細粒を有する粒界近傍部の発生を抑えるための手段としては、歪み量を増やすだけでなく、最終焼鈍の二次再結晶温度までの昇温速度の調整が効果的であることを実験［２］で知見した。 From the results of experiment [2] shown in Table 2, it was found that the generation of fine grains in the vicinity of grain boundaries can be suppressed under conditions where the temperature rise rate is relatively high, 5° C. per hour or more.
In other words, in an experiment [2], it was found that in order to suppress the generation of fine grains near the grain boundaries, it is effective not only to increase the amount of strain but also to adjust the heating rate up to the secondary recrystallization temperature in the final annealing.

以上の知見を基に、本発明の完成に至った。
すなわち、本発明は以下の要件を備える。
１．質量％で、Ｓｉ：２．０％以上７．０％以下を含む方向性電磁鋼板であって、 鋼板の圧延方向に沿う厚さ方向断面において、二次再結晶粒の粒界の圧延方向長さのうち最大長さの中心を粒界位置とし、かかる粒界位置を基点として、圧延方向に±５ｍｍの長さでかつ鋼板の全厚に亘る範囲を粒界近傍部としたとき、鋼板の全厚に亘り鋼板表面の単位面積（１ｍ^２）における前記粒界近傍部の全体に対し、結晶方位がゴス方位から１０度以上ずれている結晶粒が面積率にして２０％以下（０％含む）の割合となる粒界近傍部が５０％以上存在する方向性電磁鋼板。 Based on the above findings, the present invention has been completed.
That is, the present invention satisfies the following requirements.
1. A grain-oriented electrical steel sheet containing, by mass%, Si: 2.0% to 7.0%, wherein, in a thickness direction cross section along the rolling direction of the steel sheet, when the grain boundary position is the center of the maximum length of the grain boundary in the rolling direction of secondary recrystallized grains, and the grain boundary vicinity is a range of ± ⁵ mm in the rolling direction from the grain boundary position as a base point across the entire thickness of the steel sheet, the grain boundary vicinity is such that crystal grains whose crystal orientation deviates from the Goss orientation by 10 degrees or more account for an area ratio of 20% or less (including 0%) in 50% or more of the entire grain boundary vicinity in a unit area (1 m2) of the steel sheet surface across the entire thickness of the steel sheet.

２．前記粒界位置の全てまたは一部が、圧延方向に単位面積（１ｍ^２）における平均二次再結晶粒の粒径の整数倍の間隔で周期的に並ぶ前記１に記載の方向性電磁鋼板。 2. The grain-oriented electrical steel sheet according to 1 above, wherein all or some of the grain boundary positions are periodically arranged in the rolling direction at intervals that are an integral multiple of the average grain size of secondary recrystallized grains per unit area ( ¹ m 2 ).

３．前記１または２に記載の方向性電磁鋼板の製造方法であって、最終焼鈍前の鋼板の圧延面における片方もしくは両方の面に対し、圧下率：０．１％以上で板幅方向の一部もしくは全体に圧下を施した後、二次再結晶が開始される温度域までの昇温速度を毎時５℃以上とし、さらに１１００℃以上の温度で最終焼鈍を実施する方向性電磁鋼板の製造方法。 3. A method for producing grain-oriented electrical steel sheet as described in 1 or 2 above, in which one or both sides of the rolled surface of the steel sheet before final annealing are subjected to a rolling reduction of 0.1% or more over part or the entire sheet width direction, and then the heating rate to the temperature range where secondary recrystallization begins is set to 5°C or more per hour, and final annealing is performed at a temperature of 1100°C or more.

本発明によれば、低鉄損な方向性電磁鋼板を提供することができる。また、本発明によって提供された方向性電磁鋼板にさらなる磁区細分化処理を施すことで、極めて低鉄損な方向性電磁鋼板の製造方法を提供することができる。 According to the present invention, it is possible to provide a grain-oriented electrical steel sheet with low iron loss. In addition, by subjecting the grain-oriented electrical steel sheet provided by the present invention to further magnetic domain refining treatment, it is possible to provide a method for producing a grain-oriented electrical steel sheet with extremely low iron loss.

サンプルの圧延方向における板厚方向の鋼板断面の粒界位置の一例を表す模式図である。FIG. 2 is a schematic diagram showing an example of a grain boundary position in a steel sheet cross section in the sheet thickness direction in the rolling direction of a sample. サンプルの圧延方向における板厚方向の鋼板断面の粒界位置の他の例を表す模式図である。FIG. 11 is a schematic diagram showing another example of the grain boundary position of a steel sheet cross section in the sheet thickness direction in the rolling direction of the sample. サンプルの圧延方向における板厚方向の鋼板断面の粒界位置の他の例を表す模式図である。FIG. 11 is a schematic diagram showing another example of the grain boundary position of a steel sheet cross section in the sheet thickness direction in the rolling direction of the sample. サンプルの圧延方向における板厚方向の鋼板断面の粒界位置の他の例を表す模式図である。FIG. 11 is a schematic diagram showing another example of the grain boundary position of a steel sheet cross section in the sheet thickness direction in the rolling direction of the sample.

まず、本発明の構成要件の限定理由について述べる。
本発明は、方向性電磁鋼板製品板についての発明であり、所定の粒界付近における微細粒の面積率が本発明の要件を満たすのであれば、Ｓｉ量以外の他の成分系は特に問わない。残部はＦｅ及び不可避的不純物であってよい。さらに質量％で、Ｍｎ：０．００５～１．０００％およびＣ：０．００５０％以下の含有を許容する。さらにまた質量％で、Ｎｉ：０．０１～１．５０％、Ｃｒ：０．０１～０．５０％、Ｃｕ：０．０１～０．５０％、Ｂｉ：０．０１～０．５０％、Ｓｂ：０．０１～０．２０％、Ｓｎ：０．０１～０．２０％、Ｍｏ：０．０１～０．２０％、Ｐ：０．０１～０．２０％およびＮｂ：０．００１～０．０１５％の１種または２種以上の含有も許容する。
従って、出発材料である鋼スラブの成分組成は限定されず、二次再結晶が生じる成分組成であればよい。例えば、二次再結晶粒を成長させるためにインヒビターを利用する場合ＡｌＮ系やＭｎＳｅ系などのインヒビターが挙げられるが、これらを利用する場合のＡｌやＮ、ＭｎやＳｅなどを適量含有させればよい。 First, the reasons for restricting the constituent elements of the present invention will be described.
The present invention is an invention about a grain-oriented electrical steel sheet product, and as long as the area ratio of fine grains in the vicinity of a predetermined grain boundary satisfies the requirements of the present invention, the components other than the amount of Si are not particularly important. The balance may be Fe and unavoidable impurities. Furthermore, in mass%, Mn: 0.005 to 1.000% and C: 0.0050% or less are permitted to be contained. Furthermore, in mass%, one or more of Ni: 0.01 to 1.50%, Cr: 0.01 to 0.50%, Cu: 0.01 to 0.50%, Bi: 0.01 to 0.50%, Sb: 0.01 to 0.20%, Sn: 0.01 to 0.20%, Mo: 0.01 to 0.20%, P: 0.01 to 0.20%, and Nb: 0.001 to 0.015% are also permitted to be contained.
Therefore, the composition of the steel slab as the starting material is not limited as long as it is a composition that causes secondary recrystallization. For example, when an inhibitor is used to grow secondary recrystallized grains, an inhibitor such as an AlN-based or MnSe-based inhibitor can be used. When using these inhibitors, appropriate amounts of Al, N, Mn, Se, etc. may be contained.

また、インヒビターを利用しない方向性電磁鋼板にも同様に適用可能である。
なお、Ｓｉを鋼板に含有させることで軟磁性材料としての特性が向上するが、７．０質量％を超えて含有させた場合、著しく加工性が劣化し製造が困難になるため、本発明に用いる鋼板のＳｉ量は７．０質量％以下と限定した。好ましくは５．０％質量以下である。一方、かかるＳｉ量は、鋼板の電気抵抗を高め、渦電流損を低減し鉄損を低減可能な、２．０質量％以上とした。 The present invention is also applicable to grain-oriented electrical steel sheets that do not use an inhibitor.
Although the inclusion of Si in steel sheet improves the properties of the steel sheet as a soft magnetic material, if the content exceeds 7.0 mass%, the workability is significantly deteriorated and manufacturing becomes difficult, so the Si content of the steel sheet used in the present invention is limited to 7.0 mass% or less, and preferably 5.0 mass% or less. On the other hand, the Si content is set to 2.0 mass% or more, which is capable of increasing the electrical resistance of the steel sheet, reducing eddy current loss, and reducing iron loss.

方向性電磁鋼板は、その製造の過程において、熱延鋼板を冷間圧延したのち脱炭焼鈍を施すことで、二次再結晶の粒成長に必要な一次再結晶組織を作りこむ。この一次再結晶組織の作りこみのために、最終的に製品厚さに調整できれば、冷間圧延の回数および追加の焼鈍に関しても限定されない。 In the manufacturing process of grain-oriented electrical steel sheets, hot-rolled steel sheets are cold-rolled and then decarburized annealed to create the primary recrystallized structure necessary for the grain growth of secondary recrystallization. As long as the final product thickness can be adjusted to create this primary recrystallized structure, there are no restrictions on the number of cold rolling steps or additional annealing.

また、二次再結晶粒を小径化するために、最終焼鈍前に加工歪を入れるが、局所的に圧下による溝または歪みが導入された部分が残存した状態で、最終焼鈍を実施可能であれば、特に、そのタイミング、方法は限定されない。 In addition, to reduce the diameter of the secondary recrystallized grains, processing strain is introduced before final annealing, but there are no particular limitations on the timing or method as long as final annealing can be performed while the grooves or areas with strain introduced by localized rolling remain.

なお、この加工歪は、周期的に導入し、周期性を有することが好ましい。また、本発明でいう粒界位置は、歪み導入箇所に最も近接している二次再結晶粒における粒界位置から選択されることが望ましい。
かかる歪みの導入の周期的とは、歪間隔に一定の周期性が認められればよく、圧延方向に単位面積（１ｍ^２）における二次再結晶粒の平均粒径の整数倍の間隔で周期的に並んでいることがより好ましい。歪に周期性があることで、製造された方向性電磁鋼板から鉄心用材料を切り出す際に、場所による特性のバラつきが生じず、工業的に一定の品質を保つことが可能となるためである。
さらに、粒界位置の周期性は、歪を付与する設備の１単位が互いに隣接している少なくとも２単位分の長さの領域において粒界位置の個数比率で５０％以上であることが好ましく、８０％以上がより好ましい。 It is preferable that the processing strain is periodically introduced and has periodicity. Also, the grain boundary position in the present invention is preferably selected from the grain boundary positions of the secondary recrystallized grains that are closest to the strain introduction position.
The introduction of such strains periodically means that the strain intervals have a certain periodicity, and more preferably, the strains are periodically arranged at intervals of an integer multiple of the average grain size of secondary recrystallized grains per unit area (1 ^m2 ) in the rolling direction. This is because the periodicity of the strains prevents variations in properties from occurring depending on the location when cutting out iron core material from the manufactured grain-oriented electrical steel sheet, making it possible to maintain an industrially consistent quality.
Furthermore, the periodicity of the grain boundary positions is preferably 50% or more, and more preferably 80% or more, in terms of the number ratio of grain boundary positions in an area having a length of at least two units in which one unit of the equipment for imparting strain is adjacent to another.

ここで、本発明でいう粒界位置が周期的に存在するとは、鋼板の圧延方向へ３個以上の歪の間隔が、±０．５ｍｍ以内の誤差範囲で繰り返し導入されていることをいう。また、その間隔の値は特に限定されないが、工業的には５～２００ｍｍ程度の範囲が好ましい。 Here, the term "periodic grain boundary positions" as used herein means that three or more strains are repeatedly introduced in the rolling direction of the steel sheet with an error range of ±0.5 mm. The value of the interval is not particularly limited, but industrially, a range of about 5 to 200 mm is preferable.

二次再結晶粒の粒界は、歪みを導入した直下から圧延方向に垂直に伸びるわけではなく、歪みの前後の二次再結晶粒の蚕食スピードや、鋼板の板厚方向への歪みの不均一性の影響によって、斜めや半円状に伸びることもある。そのような影響を鑑みて上述の許容範囲を設けた。なお、歪み導入箇所の幅、長さは、歪みを導入する際に、脱炭焼鈍板へ応力、荷重が加わった部分の幅、長さとする。 The grain boundaries of secondary recrystallized grains do not extend perpendicular to the rolling direction from directly below where the strain is introduced, but may extend diagonally or in a semicircular shape due to the speed at which the secondary recrystallized grains erode before and after the strain and the influence of the non-uniformity of the strain in the thickness direction of the steel plate. The above tolerance range was set in consideration of such influences. The width and length of the area where the strain is introduced are the width and length of the part where stress and load are applied to the decarburized annealed plate when the strain is introduced.

本発明では、歪みの板幅方向の長さは、鋼板全幅に対し導入する必要はなく、鋼板の幅に対し５０％以上を満たしていれば二次再結晶粒の粒径の小径化が効果的になされ、低鉄損化した鋼板が得られる。なお、低鉄損化のためには、歪を導入する部位の幅方向の長さを大きくする方が好ましく、最も好ましい条件は、板幅方向の全てに歪みを導入することである。 In the present invention, the length of the strain in the sheet width direction does not need to be the entire width of the steel sheet. If the length is 50% or more of the width of the steel sheet, the grain size of the secondary recrystallized grains is effectively reduced, and a steel sheet with low iron loss is obtained. In order to reduce iron loss, it is preferable to increase the length in the width direction of the part where the strain is introduced, and the most preferable condition is to introduce strain in the entire sheet width direction.

また、前述の通り、導入する歪みの少なくとも個数比率で５０％以上に前述した周期性を持たせることで、鋼板を切り出した際の二次再結晶粒の粒径のばらつきを効果的に減らすことができる。 Also, as mentioned above, by making the number ratio of the introduced strain at least 50% or more the aforementioned periodicity, it is possible to effectively reduce the variation in grain size of secondary recrystallized grains when the steel sheet is cut out.

すなわち、方向性電磁鋼板を変圧器に加工する際には、ノンカットコアと呼ばれるものを除き、ある長さに剪断したのち、変圧器鉄心に組み上げる。ところが、この時、剪断後の鋼板ごとに二次再結晶粒の粒径が異なると、かかる鋼板ごとに鉄損が異なることになって、鉄損が大きい鋼板がボトルネックとなり、変圧器鉄心全体での本発明による鉄損改善効果が十分に発揮されなくなり、鉄心を磁化した際の特性を悪化させる要因になる。 In other words, when grain-oriented electrical steel sheets are processed into transformers, they are sheared to a certain length, except for those called non-cut cores, and then assembled into the transformer core. However, if the grain size of the secondary recrystallized grains differs for each steel sheet after shearing, the iron loss will differ for each steel sheet, and the steel sheets with large iron loss will become a bottleneck, preventing the iron loss improvement effect of the present invention from being fully exerted in the entire transformer core, and becoming a factor that deteriorates the characteristics when the core is magnetized.

従って、本発明では、得られた方向性電磁鋼板を用いて変圧器を作製した際に必要以上に鉄損を増加させることを抑えるために、前記した個数比率で周期的な二次再結晶粒の粒界をもつ結晶組織とすることが好ましい。 Therefore, in the present invention, in order to prevent an unnecessary increase in iron loss when a transformer is manufactured using the obtained grain-oriented electrical steel sheet, it is preferable to form a crystal structure having periodic grain boundaries of secondary recrystallized grains in the above-mentioned number ratio.

また、方向性電磁鋼板の一次再結晶組織はゴス粒に蚕食されやすく、ゴス粒の成長を助けるような組織に制御されている。しかしながら、最終焼鈍前に鋼板に局所的に歪みを導入すると、最終焼鈍の昇温中にその歪みを駆動力として、連続再結晶が発生し、再結晶粒が新たに形成されるものの、ここで生じる再結晶粒は方位が大きく異なり、蚕食されにくい。そのため、圧下部は蚕食されずに、そこを境に異なる二次再結晶粒が成長する。 In addition, the primary recrystallized structure of grain-oriented electrical steel sheet is easily encroached by Goss grains, and is controlled to a structure that aids the growth of Goss grains. However, if strain is introduced locally into the steel sheet before final annealing, continuous recrystallization occurs during the temperature rise in final annealing, driven by that strain, and new recrystallized grains are formed. However, the orientation of the recrystallized grains that are formed here is significantly different and they are not easily encroached upon. As a result, the rolling section is not encroached upon, and different secondary recrystallized grains grow across this boundary.

さらに焼鈍温度が上昇すると、成長した二次再結晶粒が間にある再結晶粒を蚕食することで、歪み部の再結晶粒が蚕食され、特定の粒径を持つ二次再結晶粒のみが作り出される。その際、歪みの導入量が適切でないと、一次再結晶粒が連続再結晶を起こすだけの駆動力に不足し、周囲の粒に対し、方位が大きくずれた粒を中心とし、そのままの方位で異常粒成長を起こす不連続再結晶が生じる。 When the annealing temperature is further increased, the grown secondary recrystallized grains eat away at the recrystallized grains in between, resulting in the recrystallized grains in the distorted areas being eroded, and only secondary recrystallized grains with a specific grain size are produced. At this time, if the amount of strain introduced is not appropriate, the primary recrystallized grains will not have enough driving force to cause continuous recrystallization, and discontinuous recrystallization will occur, with a grain whose orientation is significantly misaligned from the surrounding grains at its center, causing abnormal grain growth in that orientation.

かかる不連続再結晶は、一次再結晶粒と比べて大きく、成長したゴス粒には蚕食されない。よって、かかる不連続再結晶は最終焼鈍後も二次再結晶粒に比べて微細な結晶粒として残る。また、かかる不連続再結晶は、二次再結晶していないため結晶方位はゴス粒から大きくずれている。 These discontinuous recrystallizations are larger than the primary recrystallized grains and are not encroached upon by the grown Goss grains. Therefore, even after final annealing, these discontinuous recrystallizations remain as finer crystal grains than the secondary recrystallized grains. In addition, because these discontinuous recrystallizations are not secondary recrystallized, their crystal orientation is significantly shifted from that of the Goss grains.

すなわち、前述の実験［１］で示されたように、かかる不連続再結晶である結晶粒が少なければ鉄損がさらに改善する。
よって、本発明は、前記粒界位置を基点として、圧延方向に±５ｍｍの範囲の長さでかつ鋼板の全厚に亘る範囲を粒界近傍部としたとき、鋼板の全厚に亘り鋼板表面の単位面積（１ｍ^２）における前記粒界近傍部の全体に対し、結晶方位がゴス方位から１０度以上ずれている結晶粒（微細粒）が面積率にして２０％以下（０％含む）の割合となる粒界近傍部を、５０％以上の存在比率にすることで、極めて低鉄損な方向性電磁鋼板を得ることができる。なお、前記存在比率は８０％以上が好ましい。 That is, as shown in the above-mentioned experiment [1], if the number of crystal grains that are discontinuously recrystallized is small, the core loss is further improved.
Therefore, in the present invention, when the grain boundary vicinity is defined as a region having a length in the range of ± ⁵ mm in the rolling direction from the grain boundary position as the base point and across the entire thickness of the steel sheet, the grain boundary vicinity in which crystal grains (fine grains) whose crystal orientation deviates by 10 degrees or more from the Goss orientation account for 20% or less (including 0%) of the area ratio relative to the entire grain boundary vicinity in a unit area (1 m2) of the steel sheet surface across the entire thickness of the steel sheet is set to an abundance ratio of 50% or more, thereby making it possible to obtain a grain-oriented electrical steel sheet with extremely low iron loss. The abundance ratio is preferably 80% or more.

本発明では、母材となる鋼板の表面に歪みを導入し、かかる鋼板を加熱した際に、鋼板内の歪みを解放するために結晶粒が回復や再結晶を行うことが肝要である。
かかる導入される歪みとは、最終焼鈍前の鋼板の圧延面における片方もしくは両方の面に対し、圧下率：０．１％以上で板幅方向の一部もしくは全体に圧下を施すことである。なお、かかる圧下率の上限は、５０μｍ深さ以上の溝と成らなければ、特に限定されないが、２０μｍ以下が好ましい。 In the present invention, it is essential that strain is introduced into the surface of the steel sheet that serves as the base material, and that when the steel sheet is heated, the crystal grains undergo recovery and recrystallization in order to release the strain within the steel sheet.
The strain introduced is a reduction of 0.1% or more on one or both sides of the rolled surface of the steel sheet before final annealing, in a part or the whole of the sheet width direction. The upper limit of the reduction is not particularly limited as long as it does not result in a groove having a depth of 50 μm or more, but 20 μm or less is preferable.

また、かかる加熱に際し、昇温速度が毎時５℃未満の遅い条件では、前記した連続再結晶を起こす前に、回復によって歪みが部分的に解放され、連続再結晶を起こすだけの歪みが残らず、不連続再結晶を起こし微細粒が多く成長する。
従って、昇温速度を毎時５℃以上に速めることで、歪みによる二次再結晶粒の粒径の小径化による低鉄損化の効果をさらに大きくすることができる。 Furthermore, during such heating, if the temperature rise rate is slow, that is, less than 5° C. per hour, the strain is partially released by recovery before the above-mentioned continuous recrystallization occurs, and there is no strain remaining that is sufficient to cause continuous recrystallization, so that discontinuous recrystallization occurs and many fine grains grow.
Therefore, by increasing the temperature rise rate to 5° C. or more per hour, the effect of reducing iron loss due to the reduction in grain size of secondary recrystallized grains caused by strain can be further increased.

さらに、最終焼鈍を１１００℃以上の温度で実施する必要がある。鋼板中の不純物を純化する必要があるからである。前述した純化に、より適した温度として、１２００℃以上の保定温度で実施することが好ましい。一方、最終焼鈍の保定温度の上限は特に制限されないが、設備の能力や昇温にかかるコストを考えると１２００℃程度が好ましい。 Furthermore, the final annealing must be performed at a temperature of 1100°C or higher. This is because it is necessary to purify the impurities in the steel sheet. It is preferable to perform the annealing at a holding temperature of 1200°C or higher, which is a more suitable temperature for the purification mentioned above. On the other hand, there is no particular upper limit on the holding temperature for the final annealing, but considering the capacity of the equipment and the cost of heating, a temperature of around 1200°C is preferable.

なお、本発明において歪みを導入する際の母材である脱炭焼鈍板の製造条件は限定されず、最終焼鈍で二次再結晶が発現するプロセスであれば特に限定されない。従って、鋼板表面にレーザー照射や電気分解によるエッチングなどを施し加工した材料においても適用でき、二次再結晶粒の小径化によってさらなる低鉄損化が達成できる。 In the present invention, the manufacturing conditions of the decarburized annealed sheet, which is the base material when strain is introduced, are not limited, and are not particularly limited as long as the process results in secondary recrystallization during final annealing. Therefore, the present invention can also be applied to materials that have been processed by subjecting the steel sheet surface to laser irradiation or electrolytic etching, and further reduction in iron loss can be achieved by reducing the diameter of the secondary recrystallized grains.

また、最終焼鈍後のプロセスにおいても特に限定はされず、平坦化焼鈍や絶縁被膜の塗布、焼き付けを実施しても良い。さらに、レーザー照射に代表される熱歪の導入や、さらなる溝の形成によって、磁区細分化処理を施すことがさらなる鉄損の低減化につながるので好ましい。 The process after the final annealing is not particularly limited, and flattening annealing, application of an insulating coating, and baking may be performed. Furthermore, it is preferable to carry out a magnetic domain refining process by introducing thermal distortion, as typified by laser irradiation, or by forming further grooves, as this leads to further reduction in iron loss.

次に、実施例に基づいて本発明を具体的に説明する。以下の実施例は、本発明の代表的な一例を示すものであり、本発明は、本実施例によって何ら限定されるものではない。本発明の実施形態は、本発明の趣旨に適合する範囲で適宜変更することが可能であり、それらがいずれも本発明の技術的範囲に包含される。 Next, the present invention will be specifically described based on examples. The following examples are representative examples of the present invention, and the present invention is not limited to these examples. The embodiments of the present invention can be modified as appropriate within the scope of the invention, and all such modifications are included in the technical scope of the present invention.

表３に示す成分を含有し、残部はＦｅおよび不可避的不純物の組成になる鋼スラブを、連続鋳造にて製造し、１４２０℃にて加熱後、熱間圧延により板厚：２．０ｍｍの熱延板としたのち、９００℃で１０秒の熱延板焼鈍を施した。ついで、冷間圧延により中間板厚：１．１ｍｍとし、酸化度ＰＨ_２Ｏ／ＰＨ_２＝０．３２、温度：１０７０℃で３０秒間の中間焼鈍を施したのち、再度、冷間圧延を施し、板厚：０．２３ｍｍの冷延鋼板とした。最終板厚となった上記冷延鋼板に対し、湿水素中で、８５０℃、１５０秒間の脱炭焼鈍を施した。 A steel slab containing the components shown in Table 3 with the remainder being Fe and unavoidable impurities was produced by continuous casting, heated at 1420°C, and then hot rolled to a hot rolled sheet having a thickness of 2.0 mm, which was then annealed at 900°C for 10 seconds. Next, the intermediate thickness was reduced to 1.1 mm by cold rolling, and intermediate annealing was performed at a temperature of 1070°C for 30 seconds with an oxidation degree of _PH2O / _PH2 = 0.32, and then cold rolling was performed again to obtain a cold rolled steel sheet having a thickness of 0.23 mm. The cold rolled steel sheet having the final thickness was subjected to decarburization annealing at 850°C for 150 seconds in wet hydrogen.

その後、３～１０ｍｍ間隔でランダムに幅：５０μｍの突起が成形されている外周部の長さが２ｍの突起ロールを用いて、鋼板に対し、圧下率：０．０％、０．１％、２．０％、５．０％、１０．０％の５条件で圧下を施した。
次いで、ＭｇＯを主成分とする焼鈍分離剤を塗布し、二次再結晶、フォルステライト被膜形成を目的とし最終焼鈍を実施した。なお、圧下率：０．０％とは、鋼板表面に溝が入らない荷重を突起ロールにかけて通板したことを意味する。 Thereafter, the steel plate was subjected to reduction under five conditions of reduction ratios of 0.0%, 0.1%, 2.0%, 5.0%, and 10.0%, using a protrusion roll having an outer periphery length of 2 m on which protrusions with a width of 50 μm were formed randomly at intervals of 3 to 10 mm.
Next, an annealing separator mainly composed of MgO was applied, and final annealing was performed for the purpose of secondary recrystallization and formation of a forsterite film. The rolling reduction of 0.0% means that the steel sheet was passed through the protruding rolls with a load that did not create grooves on the steel sheet surface.

また、比較例として、脱炭焼鈍後、突起ロールによる圧延を実施せずに焼鈍分離剤を塗布し、最終焼鈍を実施するサンプルを作製した。 As a comparative example, a sample was prepared in which, after decarburization annealing, no rolling with protruding rolls was performed, an annealing separator was applied, and final annealing was performed.

最終焼鈍は、二次再結晶が開始される８００℃までは毎時１℃、毎時２℃、毎時５℃または毎時１０℃の昇温速度でそれぞれ昇温を実施し、その後はいずれも１２００℃まで毎時５℃の昇温速度で昇温するという熱パターンで実施した。 The final annealing was performed with a thermal pattern in which the temperature was increased at a rate of 1°C per hour, 2°C per hour, 5°C per hour, or 10°C per hour up to 800°C, where secondary recrystallization begins, and then increased at a rate of 5°C per hour up to 1200°C.

次に、未反応の焼鈍分離剤を取り除いたのち、５０質量％のコロイダルシリカおよび５０質量％のリン酸アルミニウムからなるコーティング液を塗布し、平坦化焼鈍も兼ねた張力コーティング焼き付け処理を焼き付け温度：８５０℃で実施した。 Next, after removing the unreacted annealing separator, a coating solution consisting of 50% colloidal silica and 50% aluminum phosphate was applied, and a tension coating baking process, which also served as flattening annealing, was carried out at a baking temperature of 850°C.

かようにして得られた方向性電磁鋼板について、エプスタイン試験および磁区観察を実施し鉄損と磁区幅を求めた。エプスタイン試験は、圧延方向に２８０ｍｍ、板幅方向に３０ｍｍのサンプルを１条件につき３６枚切り出したサンプルで、励磁条件は１．７Ｔ，５０Ｈｚで行った。
本実施例では、かかる３６枚のサンプルの鉄損値の平均を当該条件の鉄損とした。
また、磁区幅観察は、マグネットビューアーを用いて静磁状態の主磁区幅を表示させマイクロスコープで観察した。主磁区幅の観察後、鋼板断面を観察し、周期的に導入された粒界位置の個数比率、粒界近傍部における微細粒の面積率およびかかる微細粒の面積率が２０％以下の粒界近傍部の存在比率を求めた。 The grain-oriented electrical steel sheets thus obtained were subjected to an Epstein test and magnetic domain observation to determine the iron loss and magnetic domain width. The Epstein test was performed on samples cut out of 36 pieces per condition, each 280 mm in the rolling direction and 30 mm in the sheet width direction, under excitation conditions of 1.7 T and 50 Hz.
In this embodiment, the average of the iron loss values of the 36 samples was taken as the iron loss under the conditions.
The magnetic domain width was observed under a microscope using a magnet viewer to display the main magnetic domain width in a static magnetic state. After observing the main magnetic domain width, the cross section of the steel sheet was observed to determine the number ratio of periodically introduced grain boundary positions, the area ratio of fine grains in the vicinity of grain boundaries, and the abundance ratio of the vicinity of grain boundaries where the area ratio of such fine grains was 20% or less.

かかる断面の観察方法および微細粒の面積率は、前述した方法にて実施した。
なお、微細粒の面積率は１条件に付き１０枚の測定データの平均値である。
また、上記個数比率は、（周期的な粒界位置の個数／ロール外周の円周の長さの２倍の範囲内の結晶粒界の個数）の式から求めた。
さらに、上記存在比率は、（微細粒の面積率が２０％以下である粒界の数／鋼板表面の単位面積（１ｍ^２）に確認された結晶粒界数）の式から求めた。
かかる測定の結果を表４に示す。 The observation method of the cross section and the area ratio of fine particles were carried out by the methods described above.
The area ratio of fine grains is the average value of measurement data of 10 sheets per condition.
The number ratio was calculated from the formula: (number of periodic grain boundary positions/number of crystal grain boundaries within a range twice the circumferential length of the outer periphery of the roll).
Furthermore, the above-mentioned abundance ratio was calculated from the formula: (number of grain boundaries in which the area ratio of fine grains is 20% or less/number of crystal grain boundaries confirmed per unit area (1 m ² ) of the steel sheet surface).
The results of such measurements are shown in Table 4.

表４に示したように、本発明の要件を満たすことで、より優れた特性を持つ方向性電磁鋼板が得られることが分かる。
特に、上記個数比率は９３％以上の範囲で、また、上記存在比率は８８％以上の範囲で、より優れた特性を持つ方向性電磁鋼板が得られることが分かる。 As shown in Table 4, it is clear that by satisfying the requirements of the present invention, a grain-oriented electrical steel sheet having superior properties can be obtained.
In particular, it is understood that when the above number ratio is in the range of 93% or more and the above existence ratio is in the range of 88% or more, a grain-oriented electrical steel sheet having better properties can be obtained.

Claims (3)

質量％で、Ｓｉ：２．０％以上７．０％以下を含む方向性電磁鋼板であって、
鋼板の圧延方向に沿う厚さ方向断面において、二次再結晶粒の粒界の圧延方向長さのうち最大長さの中心を粒界位置とし、かかる粒界位置を基点として、圧延方向に±５ｍｍの長さでかつ鋼板の全厚に亘る範囲を粒界近傍部としたとき、
鋼板の全厚に亘り鋼板表面の単位面積（１ｍ^２）における前記粒界近傍部の全体に対し、結晶方位がゴス方位から１０度以上ずれている結晶粒が面積率にして２０％以下（０％含む）の割合となる粒界近傍部が５０％以上存在する方向性電磁鋼板。 A grain-oriented electrical steel sheet containing, by mass%, Si: 2.0% to 7.0%,
In a thickness direction cross section along the rolling direction of a steel sheet, the center of the maximum length of the grain boundary of a secondary recrystallized grain in the rolling direction is defined as a grain boundary position, and the range from the grain boundary position as a base point to a length of ±5 mm in the rolling direction and across the entire thickness of the steel sheet is defined as a grain boundary vicinity portion.
A grain-oriented electrical steel sheet in which, relative to the entire vicinity of the grain boundaries in a unit area (1 ^m2 ) of the steel sheet surface throughout the entire thickness, 50% or more of the grains in the vicinity of the grain boundaries have an area ratio of crystal grains whose crystal orientation deviates from the Goss orientation by 10 degrees or more from the Goss orientation of 20% or less (including 0%). 前記粒界位置の全てまたは一部が、圧延方向に単位面積（１ｍ^２）における二次再結晶粒の平均粒径の整数倍の間隔で周期的に並ぶ請求項１に記載の方向性電磁鋼板。 The grain-oriented electrical steel sheet according to claim 1 , wherein all or some of the grain boundary positions are periodically arranged in the rolling direction at intervals that are an integral multiple of the average grain size of secondary recrystallized grains per unit area (1 ^m 2 ). 請求項１または２に記載の方向性電磁鋼板の製造方法であって、
最終焼鈍前の鋼板の圧延面における片方もしくは両方の面に対し、圧下率：０．１％以上で板幅方向の一部もしくは全体に圧下を施した後、二次再結晶が開始される温度域までの昇温速度を毎時５℃以上とし、さらに１１００℃以上の温度で最終焼鈍を実施する方向性電磁鋼板の製造方法。 A method for producing the grain-oriented electrical steel sheet according to claim 1 or 2,
A method for producing a grain-oriented electrical steel sheet, in which one or both sides of the rolled surface of a steel sheet before final annealing are subjected to rolling reduction at a reduction rate of 0.1% or more over part or the entire sheet width direction, then the heating rate to a temperature range where secondary recrystallization begins is set to 5°C or more per hour, and final annealing is then performed at a temperature of 1,100°C or more.

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