JP4753558B2 - Method for rolling hot rolled steel strip for grain-oriented electrical steel and method for producing grain-oriented electrical steel sheet - Google Patents
Method for rolling hot rolled steel strip for grain-oriented electrical steel and method for producing grain-oriented electrical steel sheet Download PDFInfo
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- 238000005096 rolling process Methods 0.000 title claims description 86
- 229910000831 Steel Inorganic materials 0.000 title claims description 47
- 239000010959 steel Substances 0.000 title claims description 47
- 238000000034 method Methods 0.000 title claims description 24
- 229910001224 Grain-oriented electrical steel Inorganic materials 0.000 title claims description 20
- 238000004519 manufacturing process Methods 0.000 title claims description 7
- 238000010438 heat treatment Methods 0.000 claims description 52
- 238000000137 annealing Methods 0.000 claims description 22
- 239000002344 surface layer Substances 0.000 claims description 21
- 239000007789 gas Substances 0.000 claims description 15
- 239000010410 layer Substances 0.000 claims description 15
- 238000005261 decarburization Methods 0.000 claims description 13
- 239000007858 starting material Substances 0.000 claims description 13
- 229910000976 Electrical steel Inorganic materials 0.000 claims description 10
- 238000005097 cold rolling Methods 0.000 claims description 10
- 239000000203 mixture Substances 0.000 claims description 9
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 8
- 229910052760 oxygen Inorganic materials 0.000 claims description 8
- 239000001301 oxygen Substances 0.000 claims description 8
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- 230000001590 oxidative effect Effects 0.000 claims description 4
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- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical group [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 14
- 238000005098 hot rolling Methods 0.000 description 10
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- 229910052742 iron Inorganic materials 0.000 description 4
- 229910052748 manganese Inorganic materials 0.000 description 4
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- 229910052757 nitrogen Inorganic materials 0.000 description 4
- 239000011248 coating agent Substances 0.000 description 3
- 238000000576 coating method Methods 0.000 description 3
- 238000009749 continuous casting Methods 0.000 description 3
- 229910052839 forsterite Inorganic materials 0.000 description 3
- HCWCAKKEBCNQJP-UHFFFAOYSA-N magnesium orthosilicate Chemical compound [Mg+2].[Mg+2].[O-][Si]([O-])([O-])[O-] HCWCAKKEBCNQJP-UHFFFAOYSA-N 0.000 description 3
- 230000008569 process Effects 0.000 description 3
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- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 1
- 229910010413 TiO 2 Inorganic materials 0.000 description 1
- 208000009205 Tinnitus Diseases 0.000 description 1
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- 229910001873 dinitrogen Inorganic materials 0.000 description 1
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- GVALZJMUIHGIMD-UHFFFAOYSA-H magnesium phosphate Chemical compound [Mg+2].[Mg+2].[Mg+2].[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O GVALZJMUIHGIMD-UHFFFAOYSA-H 0.000 description 1
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- 230000005381 magnetic domain Effects 0.000 description 1
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
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- Soft Magnetic Materials (AREA)
- Metal Rolling (AREA)
Description
この発明は、変圧器その他電気機器の鉄心などに用いる方向性電磁鋼板製造に供せられる方向性電磁鋼用熱間圧延鋼帯の圧延方法に係り、特に高温加熱された方向性電磁鋼用スラブを熱間圧延するときに生ずる耳割れの発生を防止し、高い製品歩留りで方向性電磁鋼用熱間圧延鋼帯を製造する方法、さらにそれによって得た熱延鋼帯を用いて方向性電磁鋼板を製造する方法に関する。 The present invention relates to a rolling method of a hot rolled steel strip for directional electrical steel used in the manufacture of directional electrical steel sheets used for iron cores of transformers and other electrical equipment, and more particularly, a slab for directional electrical steel heated at high temperature. Of hot-rolled steel strip for directional electrical steel with high product yield by preventing the occurrence of ear cracks when hot-rolling steel, and directional electromagnetic using the hot-rolled steel strip obtained thereby The present invention relates to a method of manufacturing a steel plate.
方向性電磁鋼板は軟磁性材料として、主に変圧器あるいは回転機器等の鉄芯材料として使用され、磁束密度が高く、鉄損及び磁気歪が小さいことが要求される。近年のエネルギー事情の悪化、送電設備老朽化による電力投資増大に伴って、磁気特性が優れた方向性電磁鋼板を極力経済的に供給するニーズが高まっている。 The grain-oriented electrical steel sheet is used as a soft magnetic material mainly as an iron core material for a transformer or a rotating device, and is required to have a high magnetic flux density and a small iron loss and magnetostriction. With the recent deterioration of energy situation and the increase in power investment due to the aging of power transmission facilities, there is an increasing need to economically supply grain-oriented electrical steel sheets with excellent magnetic properties.
磁気特性に優れた方向性電磁鋼板を得るには、結晶粒がいわゆるゴス方位、すなわち｛110｝〈001〉方位に高度に集積した２次再結晶組織を得ることが必要である。かかる方向性電磁鋼板の一般的な製造方法は、適当なインヒビターを含む方向性電磁鋼用スラブを加熱して熱間圧延を行った後、必要に応じて熱延板焼鈍を行い、１回または中間焼鈍を挟む２回以上の冷間圧延によって最終製品板厚の冷延板を得、これに脱炭焼鈍を行った後、MgO等を主成分とする焼鈍分離剤を塗布してコイル状に巻き取り、高温仕上焼鈍が行う一連の工程からなっている。 In order to obtain a grain-oriented electrical steel sheet having excellent magnetic properties, it is necessary to obtain a secondary recrystallized structure in which crystal grains are highly accumulated in the so-called Goth orientation, that is, the {110} <001> orientation. A general method for producing such a grain-oriented electrical steel sheet is to perform hot rolling by heating a slab for grain-oriented electrical steel containing an appropriate inhibitor, and then subjecting it to hot rolling as necessary once or once. A cold-rolled sheet with the final product thickness is obtained by cold rolling at least twice with intermediate annealing, and after decarburization annealing is applied, an annealing separator mainly composed of MgO is applied to form a coil. It consists of a series of steps that are performed by winding and high-temperature finish annealing.
これらの各工程はいずれも製品品質に大きな影響を及ぼすものであるが、このうち、スラブ加熱とそれに続く熱間圧延工程は、その工程を通じて、高度にゴス方位に集積した２次再結晶組織を得るためのインヒビターを適切な析出分散状態におくという意味をもつ。そのため、スラブ加熱を1250〜1450℃という高温域かつ、長時間に亘って行ってインヒビター成分を解離固溶させ、次いで粗圧延と仕上圧延を適切な条件で行ってインヒビターの析出状態を最適化させる処理が行われる。 Each of these processes has a great impact on product quality. Of these, the slab heating and the subsequent hot rolling process have a secondary recrystallized structure that is highly accumulated in the Goth direction throughout the process. It means that the inhibitor to be obtained is in an appropriate precipitation dispersion state. Therefore, slab heating is performed in a high temperature range of 1250-1450 ° C. for a long time to dissociate and dissolve the inhibitor component, and then rough rolling and finish rolling are performed under appropriate conditions to optimize the precipitation state of the inhibitor. Processing is performed.
しかしながら、このような高温長時間のスラブ加熱を行うと、スラブ結晶粒の異常成長が誘発され、粗大化した結晶粒が発生する。この粗大化した結晶粒のうちスラブ側端部に存在するものは、粗圧延段階で圧下が掛かり難いため再結晶が進行しがたく、そのため、粗圧延後のシートバー側端部には粗い結晶粒が残り、これが熱延鋼帯の耳部に発生する割れ（以下単に「耳割れ」という）の原因となっていた。この耳割れは、続く冷延工程において鋼帯破断の原因となるために、冷間圧延に先立って耳切りが必要となり、製品歩留りの低下、ひいてはコストアップの原因となっていた。このような現象は、連続鋳造によって得た、いわゆる連鋳スラブを素材として用いた場合において特に顕著に認められる。これは、連鋳スラブでは、急速凝固に伴って生成した柱状晶組織がスラブ加熱時に異常成長し易く、かつ、粗大未再結晶粒が靭性に乏しく、熱間仕上圧延中に亀裂を生じ易くなるためである。 However, when such high-temperature and long-time slab heating is performed, abnormal growth of slab crystal grains is induced and coarse crystal grains are generated. Among the coarsened grains, those present at the slab side end are difficult to be reduced during the rough rolling stage, so that recrystallization does not proceed easily. Grain remained, which was the cause of cracks (hereinafter simply referred to as “ear cracks”) generated in the ears of the hot-rolled steel strip. Since this edge crack causes the steel strip to break in the subsequent cold rolling process, it is necessary to cut the edge prior to cold rolling, resulting in a decrease in product yield and an increase in cost. Such a phenomenon is particularly noticeable when a so-called continuous cast slab obtained by continuous casting is used as a material. This is because, in continuous cast slabs, the columnar crystal structure generated with rapid solidification tends to abnormally grow during slab heating, and coarse unrecrystallized grains have poor toughness, and cracks are likely to occur during hot finish rolling. Because.
このような耳割れを防止する手段として、例えば、特許文献１には、粗圧延時の圧下スケジュールを変更することにより粗大粒の再結晶を促進する方法が開示されている。また、特許文献２には、仕上圧延時の開始と終了の温度差を制御する方法が開示され、特許文献３には、仕上圧延前の被圧延材の長手方向・幅方向の温度差を少なくする方法が開示されている。さらに、特許文献４、特許文献５には、シートバー幅圧下を実施する方法が開示されている。
As a means for preventing such ear cracks, for example, Patent Document 1 discloses a method of promoting recrystallization of coarse grains by changing a rolling schedule during rough rolling. Patent Document 2 discloses a method for controlling the temperature difference between the start and end of finish rolling, and Patent Document 3 reduces the temperature difference in the longitudinal and width directions of the material to be rolled before finish rolling. A method is disclosed. Furthermore, Patent Literature 4 and
しかしながら、特許文献１記載の手段では、圧下スケジュールの変更が水平ロールのみに依存するため、被圧延材の側面には十分な応力が加わらず効果が乏しいという問題がある。一方、特許文献２、３に開示された手段は、いずれも仕上圧延時の被圧延材の温度不均一を小さくすることによって耳割れ防止を図るものであるが、耳割れの発生する鋼帯両側縁部（以下、単に「鋼帯耳部」という）に対して直接的に作用するものではなく、根本的な解決となっていない。また特許文献４、５に開示の手段は、スラブ加熱状況の変動の影響を受けやすく、十分に耳割れを防止できない場合があった。
However, the means described in Patent Document 1 has a problem that since the change of the rolling schedule depends only on the horizontal roll, a sufficient stress is not applied to the side surface of the material to be rolled and the effect is poor. On the other hand, the means disclosed in Patent Documents 2 and 3 both prevent ear cracks by reducing the temperature non-uniformity of the material to be rolled during finish rolling. It does not act directly on the edge (hereinafter simply referred to as “steel strip ear”) and is not a fundamental solution. In addition, the means disclosed in
本発明は、上記従来開示の手段がいずれも耳割れを根本的に解決する手段になっていないという問題点に鑑み、耳割れを効果的に防止するための方向性電磁鋼用熱間圧延鋼帯の圧延方法及び方向性電磁鋼板の製造方法を提案することを目的とする。 In view of the problem that none of the above-disclosed conventional means is a means for fundamentally solving ear cracks, the present invention provides hot rolled steel for grain-oriented electrical steel for effectively preventing ear cracks. It aims at proposing the rolling method of a band, and the manufacturing method of a grain-oriented electrical steel sheet.
本発明者は、熱間圧延前のスラブ加熱状況が耳割れの発生に及ぼす影響について詳細に調査し、スラブ加熱に伴ってスラブ表層では脱炭が進行していること、このスラブ表層の脱炭量を所定の範囲に収めたとき、特許文献５に開示のシートバー幅圧下の効果がよく現れることを知見し、これを基礎に本発明を完成するに至った。
The present inventor has investigated in detail the influence of the slab heating state before hot rolling on the occurrence of ear cracks, and that decarburization has progressed in the slab surface layer along with the slab heating, and decarburization of this slab surface layer. When the amount falls within a predetermined range, it has been found that the effect of reducing the width of the seat bar disclosed in
本発明は、出発素材の組成成分が質量比で、C：0.01〜0.08％、Si：2.5〜4.1％を含有する方向性電磁鋼用スラブに対して1250〜1450℃のスラブ加熱を施した後、粗圧延及び圧延開始温度を950〜1150℃とする仕上圧延を行う方向性電磁鋼用熱間圧延鋼帯の圧延方法であって、粗圧延に供するスラブ幅方向側面の表層5mmまでのC含有量（Cs）に対する該スラブの中心層のC含有量（Cc）の比を（Cs／Cc）としたとき、あらかじめ求められた前記比（Cs／Cc）と出発素材成分及びスラブ加熱条件との関係に基づき、前記比（Cs／Cc）が0.40以上0.86以下となるよう、前記出発素材に対するスラブ加熱条件を調整し、前記粗圧延後仕上圧延の開始までにエッジャーミルにより圧下量5〜60mmのシートバー幅圧下を行い、かつ、前記仕上圧延前のシートバー側面温度を1150〜1250℃の範囲とするものである。 In the present invention, the slab heating at 1250 to 1450 ° C. is applied to the slab for grain-oriented electrical steel containing C: 0.01 to 0.08% and Si: 2.5 to 4.1% in terms of the mass ratio of the composition components of the starting material. , A rolling method for hot rolled steel strip for directional electrical steel that performs finish rolling with rough rolling and rolling start temperature of 950 to 1150 ° C., containing C up to 5 mm in the surface layer on the side surface in the slab width direction for rough rolling When the ratio of the C content (Cc) of the central layer of the slab to the amount (Cs) is (Cs / Cc) , the ratio (Cs / Cc) obtained in advance, the starting material components, and the slab heating conditions Based on the relationship, a slab heating condition for the starting material is adjusted so that the ratio (Cs / Cc) is 0.40 or more and 0.86 or less, and a sheet having a reduction amount of 5 to 60 mm by an edger mill before the finish rolling after the rough rolling. Bar width reduction is performed, and the sheet bar side surface temperature before the finish rolling is 1150 to 1250 It is an of the range.
また、上記発明におけるスラブ加熱条件の調整をガス加熱炉の炉内酸素濃度の調整によって行うことが好適であり、その際、特にガス加熱炉の炉内酸素濃度を、容積比で0.1〜5.0％とすることが好適である。さらにスラブ加熱に当たっては、上記条件のガス加熱に続いて非酸化性雰囲気の誘導加熱が行われることとすることも効果的である。 Moreover, it is preferable to adjust the slab heating conditions in the above invention by adjusting the in-furnace oxygen concentration of the gas heating furnace, and in that case, in particular, the in-furnace oxygen concentration of the gas heating furnace is 0.1 to 5.0% by volume ratio. Is preferable. Further, in the slab heating, it is also effective to perform induction heating in a non-oxidizing atmosphere following the gas heating under the above conditions.
上記の方向性電磁鋼用熱間圧延鋼帯の圧延方法によって得た方向性電磁鋼用熱間圧延鋼帯に対して、冷間圧延、脱炭焼鈍および最終仕上焼鈍を行うことによって方向性電磁鋼板を製造することができ、それによって製品歩留まりが向上する。 By performing cold rolling, decarburization annealing and final finish annealing on the hot rolled steel strip for directional electromagnetic steel obtained by the above rolling method for hot rolled steel strip for directional electromagnetic steel. Steel sheets can be manufactured, thereby improving product yield.
本発明により、方向性電磁鋼用熱間圧延鋼帯の仕上圧延時に鋼帯耳部に生ずる耳割れを効果的に防止することができる。これによって、冷間圧延に先立つ耳切りが不要となるか、あるいは耳切り量を削減することができ、製品歩留りの向上、ひいてはコストダウンを図ることができる。 According to the present invention, it is possible to effectively prevent the edge cracks generated in the steel band edge portion during finish rolling of the hot rolled steel band for directional electromagnetic steel. This eliminates the need for edge cutting prior to cold rolling or reduces the amount of edge cutting, thereby improving product yield and thus reducing costs.
本発明は、基本的には、出発素材の組成成分が質量比で、C：0.01〜0.08％、Si：2.5〜4.1％を含有する方向性電磁鋼用スラブに対して1250〜1450℃のスラブ加熱を施した後、粗圧延及び圧延開始温度を950〜1150℃とする仕上圧延を行う方向性電磁鋼用熱間圧延鋼帯の圧延方法において、次の(1)〜(3)の条件を満たすようにすることによってその目的を達するものである。
(1)粗圧延に供するスラブ幅方向側面の表層5mmまでのC含有量（Cs）に対する該スラブの中心層のC含有量（Cc）の比を（Cs／Cc）としたとき、あらかじめ求められた前記比（Cs／Cc）と出発素材成分及びスラブ加熱条件との関係に基づき、前記比（Cs／Cc）が0.40以上0.86以下となるよう、前記出発素材に対するスラブ加熱条件を調整すること
(2)粗圧延後仕上圧延開始までにエッジャーミルにより圧下量5〜60mmのシートバー幅圧下を行うこと
(3)仕上圧延前のシートバー側面温度を1150〜1250℃の範囲とすること
以下、上記条件について順次説明する。
The present invention is basically a slab of 1250 to 1450 ° C. with respect to a slab for grain-oriented electrical steel containing the composition components of the starting material in a mass ratio of C: 0.01 to 0.08% and Si: 2.5 to 4.1%. In the rolling method of the hot rolled steel strip for directional electrical steel which performs rough rolling and finish rolling with a rolling start temperature of 950 to 1150 ° C. after heating, the following conditions (1) to (3) are satisfied. The purpose is achieved by satisfying.
(1) When the ratio of the C content (Cc) of the center layer of the slab to the C content (Cs) of the surface layer up to 5 mm on the side surface in the slab width direction subjected to rough rolling is (Cs / Cc) , it is obtained in advance. Based on the relationship between the ratio (Cs / Cc) and the starting material components and slab heating conditions, the slab heating conditions for the starting material are adjusted so that the ratio (Cs / Cc) is 0.40 or more and 0.86 or less.
(2) After the rough rolling and before the finish rolling starts, the sheet bar width is reduced by an edger mill of 5 to 60 mm.
(3) The sheet bar side surface temperature before finish rolling is set to a range of 1150 to 1250 ° C. Hereinafter, the above conditions will be sequentially described.
（出発素材成分）
本発明の出発素材であるスラブの基本組成は、C：0.01〜0.08％、Si：2.5〜4.1％を含有するものであり、必要に応じてMn：0.03〜0.10％、S及びSeの１種または２種（合計量）：0.005〜0.1％、sol.Al：0.01〜0.05％、N：0.004〜0.012％を含有し、残部は不可避的不純物を除きFeからなる。
(Starting material components)
The basic composition of the slab, which is the starting material of the present invention, contains C: 0.01 to 0.08%, Si: 2.5 to 4.1%, and Mn: 0.03 to 0.10% as necessary, one of S and Se Or 2 types (total amount): 0.005-0.1%, sol.Al:0.01-0.05%, N: 0.004-0.012% is contained, and the remainder consists of Fe except an unavoidable impurity.
Cは熱間圧延時のα−γ変態を利用して結晶組織の改善を行うために有効であるが、多すぎると脱炭が困難となるため、0.01〜0.08％の範囲とする。Siは少なすぎると鋼板の電気抵抗が小さくなって渦電流損が増大するため鉄損が劣化し、多すぎると冷間圧延が困難となり破断等によるスクラップ増大につながるので2.5〜4.1％の範囲とする。Mnはインヒビターを形成する成分であるが、過剰になるとインヒビターの粒子径が粗大化して粒成長抑制力が低下するため、0.08〜0.10％の範囲とする。Se及びSは、MnやCuとともにインヒビターを形成する成分であるが、過剰になると熱間圧延時の粒界割れに起因する表面欠陥が増大し、また仕上焼鈍時の純化が困難となるという問題を生ずるため、合計で0.005〜0.1％の範囲とする。Al及びNはインヒビターとしてAlNを形成する成分である。Alは少なすぎると磁束密度が低下し、多すぎると２次再結晶の発現が安定しなくなるので、Alはsol.Al（酸可溶性Al）として0.01〜0.05％の範囲とし、Nは少なすぎると磁束密度が低下し、多すぎるとスラブ加熱中のふくれに起因する表面欠陥が増大するため、0.004〜0.012％の範囲とする。 C is effective for improving the crystal structure by utilizing the α-γ transformation during hot rolling, but if it is too much, decarburization becomes difficult, so 0.01 to 0.08% is set. If Si is too small, the electrical resistance of the steel sheet will decrease and eddy current loss will increase, so iron loss will deteriorate. If it is too much, cold rolling will be difficult and scrap will increase due to breakage, etc. To do. Mn is a component that forms an inhibitor, but if it is excessive, the particle diameter of the inhibitor becomes coarse and the grain growth inhibiting power decreases, so the content is made 0.08 to 0.10%. Se and S are components that form inhibitors together with Mn and Cu. However, if excessive, surface defects due to grain boundary cracking during hot rolling increase, and purification during finish annealing becomes difficult. Therefore, the total content is set to 0.005 to 0.1%. Al and N are components that form AlN as an inhibitor. If the Al content is too small, the magnetic flux density will decrease. If the Al content is too large, the secondary recrystallization will not be stable, so Al should be in the range of 0.01-0.05% as sol.Al (acid-soluble Al). If the magnetic flux density decreases and is too large, surface defects due to blistering during slab heating increase, so the range is 0.004 to 0.012%.
上記基本組成に加えて、磁気特性の改善のために、粒界偏析型インヒビターとしてSbやSnを含有させることができる。ただし、その含有量が少なすぎると磁気特性の改善効果が少なく、多すぎると脆性低下やフォルステライト質絶縁被膜への悪影響が生じるので、含有させる場合は、0.01〜0.05％の範囲とするのが好適である。また、フォルステライト質絶縁被膜の性状を向上させるために、0.03〜0.20％のCuを含有させることが有効である。さらに、熱間圧延時の表面α−γ変態を利用して結晶組織の改善を行うために、0.05〜0.3％のNiを含有させることも有効である。これら元素は、それぞれ単独で、あるいは任意に組み合わせて含有させることによって、所期の効果を得ることができる。なお、残部は、不可避的不純物を除きFeであるが、方向性電磁鋼板の製造の際に任意に添加可能とされている諸元素、たとえばCr、Mo、P等を含有させることも可能である。 In addition to the above basic composition, Sb or Sn can be contained as a grain boundary segregation inhibitor for improving magnetic properties. However, if the content is too small, the effect of improving the magnetic properties is small. If the content is too large, the brittleness is lowered and the forsterite insulating film is adversely affected. Is preferred. In order to improve the properties of the forsterite insulating coating, it is effective to contain 0.03-0.20% Cu. Furthermore, in order to improve the crystal structure by utilizing the surface α-γ transformation during hot rolling, it is also effective to contain 0.05 to 0.3% Ni. Each of these elements can be used alone or in any combination to obtain the desired effect. The balance is Fe except for inevitable impurities, but it is also possible to contain various elements that can be arbitrarily added in the production of grain-oriented electrical steel sheets, such as Cr, Mo, P, etc. .
上記組成を有する出発素材は、所定の組成を有する溶鋼を準備し、これを公知の方法、たとえば通常の造塊法又は連続鋳造法によってスラブとすることによって製造することができる。 The starting material having the above composition can be produced by preparing molten steel having a predetermined composition and making it into a slab by a known method, for example, a normal ingot-making method or a continuous casting method.
（スラブ加熱条件）
上記出発素材であるスラブは、プッシャー式、ウォーキングビーム式のスラブ加熱炉を用い、さらに必要に応じてスラブ加熱炉に引き続いて設けられた誘導加熱炉を用いて高温加熱される。この際の加熱温度は、1250℃より低いとインヒビター成分の固溶が不十分となり後続の圧延過程で十分な析出分散相を形成することができなくなり、1450℃より高いと膨大なスケールの発生によって歩留低下及び加熱炉の寿命低下を招くので1250〜1450℃とする。
(Slab heating conditions)
The slab, which is the starting material, is heated at high temperature using a pusher type or walking beam type slab heating furnace and, if necessary, an induction heating furnace provided after the slab heating furnace. If the heating temperature at this time is lower than 1250 ° C, the inhibitor component is not sufficiently dissolved, and a sufficient precipitated dispersed phase cannot be formed in the subsequent rolling process. If the heating temperature is higher than 1450 ° C, a huge scale is generated. The yield is lowered and the life of the heating furnace is shortened, so the temperature is set to 1250 to 1450 ° C.
本発明では、このスラブ加熱段階において、粗圧延に供するスラブの幅方向側面の表層5mm（以下単に「スラブ表層5mm」という）までのC含有量（Cs）に対する該スラブの中心層（以下単に「スラブ中心層」という）のC含有量（Cc）の比（Cs／Cc）を0.40以上0.86以下となるようスラブ加熱条件を調整する。
In the present invention, in this slab heating step, the center layer of the slab (hereinafter simply referred to as “
図１は、C：0.058％、Si：3.0％、Mn：0.071％、S：0.018％、N：0.005％、残部不可避的不純物を除きFeからなる方向性電磁鋼板用スラブをウォーキングビーム式のスラブ加熱炉を用いて1250〜1450℃で加熱し、粗圧延、エッジャー幅圧下さらに仕上圧延を行ったときの、スラブ表層5mmまでのC含有量（Cs）に対するスラブ中心層のC含有量（Cc）の比（Cs／Cc）と仕上圧延された熱延鋼帯耳部に生じた耳割れ深さとの関係を示すグラフである。図１に示すように、Cs／Cc比を0.40〜0.86とすることによって耳割れ深さを小さくできる。 Fig. 1 shows walking beam slabs for grain-oriented electrical steel slabs made of Fe except for C: 0.058%, Si: 3.0%, Mn: 0.071%, S: 0.018%, N: 0.005%, and the remainder unavoidable impurities. C content (Cc) of slab center layer with respect to C content (Cs) up to 5mm of slab surface layer when heated at 1250-1450 ° C using a heating furnace, rough rolling, edger width pressure, and finish rolling It is a graph which shows the relationship between the ratio (Cs / Cc) of this, and the depth of the ear crack produced in the hot-rolled steel strip ear part by finish rolling. As shown in FIG. 1, the ear crack depth can be reduced by setting the Cs / Cc ratio to 0.40 to 0.86.
なお、上記結果を得たときのスラブ表層5mmまでのC含有量（Cs）、スラブ中心層のC含有量（Cc）は、仕上圧延に供されたものと同一の組成を有するスラブを仕上圧延に供されたものと同一の条件でスラブ加熱したものを冷却後、スラブ厚さ方向の中央部、かつスラブ長さ方向の中央部においてスラブ側面に対して垂直方向（スラブ幅方向）にドリリングし、そのときスラブ表面から5mmまで得られる切粉によってスラブ表層5mmまでのC含有量（Cs）を決定し、さらにドリリングを進めてスラブ幅方向中心部に達したときの幅方向5mmの切粉によってスラブ中心層のC含有量（Cc）を決定したものである。また、耳割れ深さは、仕上圧延によって得られたコイル状の熱延鋼帯について巻直し検査を行って熱延鋼帯に現れる耳割れ深さを個別に測定し、その熱延鋼帯全長での最大値をもって耳割れ深さとしたものである。また、エッジャー幅圧下量は5〜60mm、仕上圧延前シートバー側面温度は1150〜1250℃の範囲のものとした。 When the above results are obtained, the slab surface layer up to 5 mm C content (Cs), the slab center layer C content (Cc), finish rolling a slab having the same composition as that used for finish rolling After cooling the slab heated under the same conditions as those provided for the slab, drilling is performed perpendicularly to the slab side (slab width direction) at the center of the slab thickness direction and at the center of the slab length direction. Then, the C content (Cs) up to 5mm from the slab surface is determined by the chips obtained from the slab surface up to 5mm, and further drilling is carried out to achieve the center of the slab width direction. The C content (Cc) of the slab center layer is determined. In addition, the ear crack depth is measured by rewinding the coiled hot-rolled steel strip obtained by finish rolling and measuring the ear-crack depth that appears in the hot-rolled steel strip individually. The maximum value at is the ear crack depth. Further, the edger width reduction amount was 5 to 60 mm, and the sheet bar side surface temperature before finish rolling was in the range of 1150 to 1250 ° C.
このようなスラブの表層5mmまでのC含有量（Cs）に対する該スラブの中心層のC含有量（Cc）の比（Cs／Cc）が上記範囲外にあるときに耳割れが顕著になる原因は、Cs／Ccが0.40より低い場合には、表層脱炭が大きいため、表層近傍がα単相となってα−γ変態による組織改善がなされずにスラブ結晶粒の粗大化が過大に進行して耳割れの発生が完全に防止できなくなるためであり、一方、0.86より高い場合には、表層の脱炭層すなわちα単相部が薄いためにその直下にあるα＋γ相に生成したボイドがシートバーの表層部に容易に到達して、スラブ結晶粒に関係なく深い耳割れが発生するためであると推定される。 Causes of ear cracking when the ratio (Cs / Cc) of the C content (Cc) of the center layer of the slab to the C content (Cs) up to 5 mm of the surface layer of such a slab is outside the above range When Cs / Cc is lower than 0.40, the surface layer decarburization is large, so the surface layer becomes α single phase and the structure is not improved by α-γ transformation, and the slab crystal grains become excessively coarse. On the other hand, if it is higher than 0.86, the surface decarburized layer, that is, the α single-phase part is thin, so the void generated in the α + γ phase immediately below it is a sheet. It is presumed that this is because it easily reaches the surface layer of the bar and deep ear cracks occur regardless of the slab crystal grains.
したがって、本発明では、スラブ加熱時においてスラブの表層5mmまでのC含有量、いい換えれば表層の脱炭量と脱炭深さを最適範囲に調整し、それによって（Cs／Cc）を上記範囲内に収めるようにすることが必要である。このような（Cs／Cc）比は、スラブ加熱をガス加熱炉によって行う場合には、ガス加熱炉内の酸素濃度を調整すること、具体的には0.1〜5.0％の範囲内で調整することによって達成できる。なお、ガス加熱炉に続いて誘導加熱炉を設置してスラブ過熱を行う場合には、ガス加熱炉内の雰囲気調整によってスラブ表層の脱炭量と脱炭深さを調整し、誘導加熱炉の雰囲気は非酸化性とすることが望ましい。 Therefore, in the present invention, when the slab is heated, the C content up to 5 mm of the surface layer of the slab, in other words, the amount of decarburization and the depth of decarburization of the surface layer are adjusted to the optimum range, thereby (Cs / Cc) within the above range. It is necessary to keep it inside. Such (Cs / Cc) ratio should be adjusted within the range of 0.1 to 5.0% by adjusting the oxygen concentration in the gas heating furnace when slab heating is performed by a gas heating furnace. Can be achieved. In addition, when installing an induction heating furnace after the gas heating furnace and performing slab overheating, the decarburization amount and decarburization depth of the slab surface layer are adjusted by adjusting the atmosphere in the gas heating furnace, and the induction heating furnace The atmosphere is preferably non-oxidizing.
図２は、図１を得たのと同様の条件によってスラブ加熱炉、粗圧延、エッジャー幅圧下さらに仕上圧延を行ったときの、エッジャー幅圧下量と仕上圧延された熱延鋼帯に生じた耳割れ深さとの関係を、仕上圧延前シートバー側面温度をパラメータとして現したグラフである。上記の結果から、エッジャー幅圧下量を5mm以上とすると耳割れ深さが小さくなり、かつその効果は仕上圧延前シートバー側面温度が1200℃と高い場合に十分小さくなることが分かる。なお、この場合におけるスラブの表層5mmまでのC含有量（Cs）、該スラブの中心層のC含有量（Cc）の決定方法は、図１を得たときと同様であり、Cs／Cc比は、0.60〜0.70と平均的なレベルとし、仕上圧延前耳部温度は、1000±25℃と1200±25℃の２レベルとした。 FIG. 2 is generated in the hot rolled steel strip subjected to the edger width reduction and finish rolling when the slab heating furnace, rough rolling, edger width reduction and finish rolling are performed under the same conditions as in FIG. It is the graph which expressed the relationship with the ear crack depth by using the sheet bar side surface temperature before finish rolling as a parameter. From the above results, it can be seen that when the edger width reduction amount is 5 mm or more, the ear crack depth becomes small, and the effect becomes sufficiently small when the sheet bar side surface temperature before finish rolling is as high as 1200 ° C. In this case, the method for determining the C content (Cs) up to 5 mm of the surface layer of the slab and the C content (Cc) of the central layer of the slab is the same as in obtaining FIG. 1, and the Cs / Cc ratio Is an average level of 0.60 to 0.70, and the ear temperature before finishing rolling is two levels of 1000 ± 25 ° C. and 1200 ± 25 ° C.
図３は、図１を得たのと同様の条件によってスラブ加熱炉、粗圧延、エッジャー幅圧下さらに仕上圧延を行ったときの、仕上圧延前シートバー側面温度と仕上圧延された熱延鋼帯に生じた耳割れ深さとの関係を示すグラフである。この結果から、仕上圧延前シートバー側面温度を1150℃より高くすることにより耳割れ深さを小さくできることが分かる。なお、この場合におけるスラブの表層5mmまでのC含有量（Cs）、該スラブの中心層のC含有量（Cc）の決定方法は、図１を得たときと同様であり、Cs／Cc比が0.60〜0.70と平均的なレベル、かつエッジャー幅圧下量が5〜60mmであるものによった。 FIG. 3 shows the sheet bar side surface temperature before finish rolling and the hot-rolled hot-rolled steel strip when finish rolling is performed under the same conditions as those obtained in FIG. It is a graph which shows the relationship with the ear crack depth which arose. From this result, it can be seen that the depth of the edge crack can be reduced by raising the temperature of the side of the sheet bar before finish rolling to higher than 1150 ° C. In this case, the method for determining the C content (Cs) up to 5 mm of the surface layer of the slab and the C content (Cc) of the central layer of the slab is the same as in obtaining FIG. 1, and the Cs / Cc ratio The average level was 0.60 to 0.70, and the edger width reduction amount was 5 to 60 mm.
上記から明らかなように、本発明では、粗圧延後仕上圧延開始までの間にエッジャーミルにより圧下量5〜60mmのシートバー幅圧下を行うこと、及び仕上圧延前シートバー側面温度を1150〜1250℃の範囲とすることが必要である。前者は、過大なシートバー幅圧下による形状不良（ドッグボーン形成）を防止できる範囲内で、シートバー側面のうねりを矯正し、それによって不均一な幅拡がりと局部的な応力集中に基づく耳部の内部のクラック発生を防止するための条件である。後者は、内部クラックの発生が、スラブの高温加熱によって一旦固溶したMnS等が温度低下の大きい鋼帯耳部において粗大に成長・析出し、その周囲に微小なボイドが生成し、圧延時の３軸応力下でボイドがクラックに発展するものと考えられることに基づき、該メカニズムが機能しないようにするための条件である。なお、仕上圧延前シートバー側面温度は、たとえば側面の板方向中央部について放射温度計により測定することができる。 As is clear from the above, in the present invention, the sheet bar width is reduced by an edger mill between the rough rolling and the finish rolling until the start of finishing rolling, and the sheet bar side surface temperature before finishing rolling is 1150 to 1250 ° C. It is necessary to be within the range. The former corrects waviness on the side of the seat bar within a range that can prevent shape defects due to excessive sheet bar width reduction (dogbone formation), thereby making the ear part based on uneven width expansion and local stress concentration This is a condition for preventing the occurrence of cracks inside. In the latter, the occurrence of internal cracks, such as MnS once dissolved by high-temperature heating of the slab, grows and precipitates coarsely in the steel band ears where the temperature drop is large, and minute voids are generated around it. This is a condition for preventing the mechanism from functioning based on the fact that voids are considered to develop into cracks under triaxial stress. In addition, the sheet bar side surface temperature before finish rolling can be measured, for example, with a radiation thermometer at the center portion in the plate direction of the side surface.
これらの条件を満たすためには、第一に粗圧延機の最終スタンド出側と仕上圧延機第１スタンド入側との間にエッジャーを配置して5〜60mmの範囲でシートバーの幅圧下を行い得るようにすればよい。幅圧下量は、5〜60mmの間であれば、耳割れ深さに対する効果の差異は認められないが、仕上圧延前シートバー側面温度が低いときはシートバーの幅圧下量を大きく取り過ぎると形状不良（ドッグボーン）が生じやすくなるので、5〜40mmとするのが好適である。一方、仕上圧延前シートバー側面温度は、たとえば、エッジバーナーや保熱カバーを用いて調節することが可能である。 In order to satisfy these conditions, first of all, an edger is placed between the final stand exit side of the roughing mill and the finish stand first stand entry side to reduce the width of the sheet bar within a range of 5 to 60 mm. It can be done. If the width reduction amount is between 5 and 60 mm, there is no difference in the effect on the ear crack depth, but if the sheet bar side surface temperature before finish rolling is low, if the width reduction amount of the sheet bar is too large Since shape defects (dogbone) are likely to occur, the thickness is preferably 5 to 40 mm. On the other hand, the sheet bar side surface temperature before finish rolling can be adjusted using, for example, an edge burner or a heat insulating cover.
本発明においては、上記粗圧延後仕上圧延の間にエッジャーミルにより圧下量5〜60mmのシートバー幅圧下を行うこと及び仕上圧延前シートバー側面温度を1150〜1250℃の範囲とすることを遵守しながら熱間圧延を行なうが、その際、仕上圧延の開始条件は、電磁鋼板用熱延鋼板の熱延集合組織上の要求により950〜1150℃とする。なお、仕上圧延前シートバー側面温度は1150〜1250℃と熱延鋼板の仕上圧延開始温度より高いが、その範囲は端部から極く狭いたとえば50mm程度であり、仕上圧延中に急速に温度低下するので、電磁鋼板の特性に大きな影響をもたらさない。 In the present invention, the sheet bar width is reduced by an edger mill between the rough rolling and the finish rolling, and the sheet bar side surface temperature before finishing rolling is set in the range of 1150 to 1250 ° C. However, in this case, the finish rolling start condition is 950 to 1150 ° C. depending on the hot rolling texture of the hot rolled steel sheet for electrical steel sheet. In addition, the sheet bar side surface temperature before finish rolling is 1150-1250 ° C, which is higher than the finish rolling start temperature of hot-rolled steel sheets, but the range is very narrow, for example, about 50 mm from the end, and the temperature drops rapidly during finish rolling. Therefore, it does not have a great influence on the properties of the electrical steel sheet.
本発明により、耳割れ深さが3mm以下の熱延鋼帯を得ることができる。また、得られた熱延鋼帯の耳部形状はドッグボーンに起因する二枚板の発生もなく、極めて良好であった。 According to the present invention, a hot-rolled steel strip having an ear crack depth of 3 mm or less can be obtained. Further, the shape of the ear portion of the obtained hot-rolled steel strip was very good with no occurrence of double plates due to dogbone.
このようにして得られた熱延鋼帯は、常法により冷間圧延、脱炭焼鈍および最終仕上焼鈍を行って方向性電磁鋼板に仕上げられる。そのための条件は、一般的に採用され得るものにしたがえばよい。そのような一般的な手段を例示すると以下のとおりである。すなわち、必要に応じて、800℃以上1100℃以下を好適とする熱延板焼鈍を施し、次いで１回又は中間焼鈍を挟む２回以上の冷間圧延を施して最終仕上厚の冷延板とする。得られた冷延板に対し脱炭焼鈍を施し、さらに焼鈍分離剤を塗布し、1200℃前後の高温で最終仕上焼鈍を施し、二次再結晶組織を発達させるとともにフォルステライト被膜を表面に形成させる。最終仕上焼鈍後、必要に応じて平坦化焼鈍によって形状矯正を行い、鉄損を改善するために、鋼板表面に張力を付与する絶縁コーティングを施す。なお、いわゆる高磁束密度電磁鋼板の製造に当たって採用されている種々の手段、たとえば、鏡面化処理、磁区細分化処理、脱炭焼鈍後の浸珪法などの採用は自由であり、本発明の効果を妨げるものではない。 The hot-rolled steel strip thus obtained is finished into a grain-oriented electrical steel sheet by performing cold rolling, decarburization annealing and final finish annealing by a conventional method. The conditions for this may be in accordance with those that can be generally adopted. Examples of such general means are as follows. That is, if necessary, hot-rolled sheet annealing that is preferably 800 ° C. or higher and 1100 ° C. or lower is performed, and then cold rolling is performed once or two or more times with intermediate annealing between them to obtain a cold-rolled sheet having a final finished thickness. To do. The resulting cold-rolled sheet is decarburized and annealed, and then an annealing separator is applied, and final finish annealing is performed at a high temperature of around 1200 ° C to develop a secondary recrystallized structure and form a forsterite film on the surface. Let After final finish annealing, shape correction is performed by flattening annealing as necessary, and an insulating coating that applies tension to the steel sheet surface is applied to improve iron loss. It should be noted that various means employed in the production of so-called high magnetic flux density electrical steel sheets, such as mirror finishing, magnetic domain subdivision, and siliconization after decarburization annealing, are free, and the effects of the present invention It does not prevent.
質量比で、C：0.071％、Si：3.80％、Mn：0.066％、Se：0.020％、So1.Al：0.026％、N：0.009％、およびSb：0.037％を含有し、残部がFeおよび不可避的不純物から成る組成の溶鋼を連続鋳造によって210mm厚のスラブとし、ガス加熱炉によって1200℃の温度で加熱し、引き続いて誘導加熱炉によって非酸化性雰囲気下で1380〜1410℃に加熱した後、最終圧下率50％の粗圧延を行って35mm厚のシートバーとし、仕上圧延開始温度1040〜1120℃の範囲で仕上圧延を行い、板厚2.6mmに熱間圧延した。 Contains C: 0.071%, Si: 3.80%, Mn: 0.066%, Se: 0.020%, So1.Al: 0.026%, N: 0.009%, and Sb: 0.037%, with the balance being Fe and inevitable After the molten steel having a composition composed of mechanical impurities is made into a 210 mm thick slab by continuous casting, heated at a temperature of 1200 ° C. by a gas heating furnace, and subsequently heated to 1380-1410 ° C. in a non-oxidizing atmosphere by an induction heating furnace, A rough rolling with a final reduction ratio of 50% was performed to obtain a 35 mm-thick sheet bar, and finish rolling was performed at a finishing rolling start temperature in the range of 1040 to 1120 ° C. to hot rolling to a sheet thickness of 2.6 mm.
このとき、保熱カバーとエッジヒーターを併用することによって仕上圧延前シートバー側面温度を調整するとともに、シートバー幅圧下量をエッジャーミルの圧下量を調整して変化させた。また、ガス加熱炉内への窒素ガス供給量を制御してガス炉内の酸素濃度を変化させて粗圧延に供するスラブ表層5mmまでのC含有量（Cs）に対するスラブ中心層のC含有量（Cc）の比（Cs／Cc）を変化させた。この制御は、あらかじめ行った予備試験により成分レベルごとにとったスラブ表層5mmまでのC含有量（Cs）とスラブ中心層のC含有量（Cc）の値、さらにはこれらの比（Cs／Cc）をテーブル化し、該テーブルに基づきガス炉内の酸素濃度を制御することによって行った。これら操業データは表１にまとめて示す。 At this time, the side bar temperature before finish rolling was adjusted by using the heat retaining cover and the edge heater together, and the sheet bar width reduction amount was changed by adjusting the reduction amount of the edger mill. In addition, the C content in the slab center layer (Cs) up to 5mm in the slab surface layer (Cs) used for rough rolling by changing the oxygen concentration in the gas furnace by controlling the supply amount of nitrogen gas into the gas heating furnace ( The ratio of Cc) (Cs / Cc) was varied. This control is based on the C content (Cs) of the slab surface layer up to 5 mm and the C content (Cc) of the slab center layer, and the ratio of these (Cs / Cc). ) Was made into a table and the oxygen concentration in the gas furnace was controlled based on the table. These operational data are summarized in Table 1.
次いで得られた熱延板に対し、1000℃×30minの熱延板焼鈍を行い、1115℃×30ｓの中間焼鈍を挟む２回の冷間圧延によって厚さ0.30mmの最終冷延板とした。得られた冷延板をアルカリ脱脂して表面を清浄化した後、湿水素雰囲気中にて840℃×120sの脱炭焼鈍を行った。次いで、質量比で5％のTiO2を含有するMgO系焼鈍分離剤を塗布し、H2雰囲気中での1200℃×10hの仕上焼鈍を行った。この後、リン酸マグネシウムとコロイダルシリカを主成分とするコーティングを施した。かくして得られた製品の磁界800A／mにおける磁束密度B8、1.7T−50Hzにおける鉄損W17／50について調査した結果を表１にあわせて示す。 Next, the obtained hot-rolled sheet was subjected to hot-rolled sheet annealing at 1000 ° C. for 30 minutes, and a final cold-rolled sheet having a thickness of 0.30 mm was obtained by two cold rollings sandwiching an intermediate annealing at 1115 ° C. for 30 seconds. The obtained cold-rolled sheet was alkali degreased to clean the surface, and then decarburized and annealed at 840 ° C. for 120 s in a wet hydrogen atmosphere. Next, an MgO-based annealing separator containing 5% TiO 2 by mass was applied, and finish annealing was performed at 1200 ° C. for 10 hours in an H 2 atmosphere. Thereafter, a coating mainly composed of magnesium phosphate and colloidal silica was applied. Table 1 shows the results of investigation on the magnetic flux density B 8 at a magnetic field of 800 A / m and the iron loss W 17/50 at 1.7 T-50 Hz of the product thus obtained.
表１に示すとおり、本発明の条件を満たすNo.1〜10では耳割れが小さく、形状も良好であり、最終製品の磁気特性も優れている。これに対し、ガス加熱炉の酸素濃度が0.1〜5.0％（容積比）の範囲を外れたためにCs／Ccが0．40〜0.86の範囲を外れたNo.11〜14では耳割れ深さが大きい。また、エッジャー幅幅圧下量が5〜60mmの範囲を外れたNo.15〜18では耳割れ深さが大きいか、過大のドッグボーンにより座屈が生じ、製品板の板厚偏差が増大するという形状不良が発生している。そして、仕上圧延前耳部温度が1150℃より低いNo.19〜20では耳割れが大きく、かつ磁気特性も若干劣っている。 As shown in Table 1, Nos. 1 to 10 satisfying the conditions of the present invention have small ear cracks, good shape, and excellent final product magnetic properties. On the other hand, No.11-14 where Cs / Cc was out of the range of 0.40-0.86 because the oxygen concentration of the gas heating furnace was out of the range of 0.1-5.0% (volume ratio), the ear crack depth was large. In addition, in No.15-18 where the edger width width reduction amount is outside the range of 5-60 mm, the ear crack depth is large, or buckling occurs due to excessive dogbone, increasing the thickness deviation of the product plate A shape defect has occurred. And in No. 19-20 whose ear part temperature before finish rolling is lower than 1150 degreeC, an ear crack is large and a magnetic characteristic is also inferior slightly.
Claims (5)
粗圧延に供するスラブ幅方向側面の表層5mmまでのC含有量（Cs）に対する該スラブの中心層のC含有量（Cc）の比を（Cs／Cc）としたとき、あらかじめ求められた前記比（Cs／Cc）と前記出発素材成分及びスラブ加熱条件との関係に基づき、前記比（Cs／Cc）が0.40以上0.86以下となるよう、前記出発素材に対するスラブ加熱条件を調整し、
前記粗圧延後仕上圧延開始までにエッジャーミルにより圧下量5〜60mmのシートバー幅圧下を行い、かつ、
前記仕上圧延前の仕上圧延前シートバー側面温度を1150〜1250℃とすることを特徴とする方向性電磁鋼用熱間圧延鋼帯の圧延方法。 After slab heating at 1250 to 1450 ° C. is performed on a slab for grain-oriented electrical steel containing C: 0.01 to 0.08% and Si: 2.5 to 4.1% by mass ratio of the starting material composition, rough rolling and A rolling method of a hot rolled steel strip for directional electrical steel that performs finish rolling with a rolling start temperature of 950 to 1150 ° C,
When the ratio of the C content (Cc) of the central layer of the slab to the C content (Cs) of the surface layer up to 5 mm on the side surface in the slab width direction subjected to rough rolling is (Cs / Cc) , the ratio obtained in advance Based on the relationship between (Cs / Cc) and the starting material component and the slab heating condition, the slab heating condition for the starting material is adjusted so that the ratio (Cs / Cc) is 0.40 or more and 0.86 or less,
After the rough rolling and before the start of finish rolling, the sheet bar width is reduced by an edger mill of 5 to 60 mm, and
A rolling method of a hot-rolled steel strip for grain-oriented electrical steel, characterized in that the side-bar surface temperature before finishing rolling before finishing rolling is 1150 to 1250 ° C.
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