JP3716432B2 - Heating method of slab for grain-oriented electrical steel sheet - Google Patents

Description

【０００１】
【産業上の利用分野】
本発明は、方向性電磁鋼板の製造方法に関し、特に、その製造用スラブを熱間圧延する前の加熱技術に関するものである。
【０００２】
【従来の技術】
周知のように、方向性電磁鋼板の優れた磁気特性は、板面に（１００）面、圧延方向に＜００１＞軸の２次再結晶粒を、最終焼鈍により選択的に発達させることによって得られる。そのためには、鋼中にインヒビタと呼ばれる微細な析出物、例えばＭｎＳ，ＭｎＳｅ，ＡｌＮ等を析出させることが肝要であり、このインヒビタの分散形態のコントロールは、これら析出物を一旦固溶させた後、熱間圧延を施すことによって行われる。
【０００３】
ところで、このような目的で行われる熱間圧延前のスラブ加熱は、インヒビタ成分の再固溶のため、例えばガスバーナ加熱タイプの炉（以下「ガス炉」）による１３５０℃以下の温度での１次加熱後に、誘導加熱タイプの炉（以下「Ｉ炉」という。これは、スラブを厚み方向を底部とし、所謂Ｉ形状で炉内に静置、加熱するための呼び名で、炉内ではスラブ幅方向が高さに相当する。）で行われていた。その２次加熱温度は、スラブに粗大析出したインヒビターを再固溶可能とする１４００℃〜１４８０℃であり、この２次加熱後、スラブは熱間圧延を施されていた。
【０００４】
上記工程のＩ炉段階において、図２に示すように、スラブ１長手方向の両端部近傍（それぞれＬＥ，ＴＥ端部という）が、炉の構造上放射熱が大きいため、それ以外の中央部側に対して５℃〜３０℃低めとなる傾向があった。したがって、従来はスラブ両端部近傍にインヒビタの再固溶不足が生じて、最終製品の方向性電磁鋼板は磁性不良となりやすかった。この問題を解決するための方法として、特開平５−５９４３７号公報は，Ｉ炉３内の両端部でスラブとの間に生じる空間４に、誘導発熱板及び断熱材を配置し、補助加熱する技術を開示している。また、特開昭５９−１９３２１６号公報は、ガスバーナ加熱の１次加熱時に、スラブの長手方向に対して、図３に示すような所謂テーパ加熱技術を教えた。これは、熱間圧延前のスラブ加熱において、圧延方向後端部の温度が前端部よりも２００℃の範囲内で高くなるように加熱する技術である。
【０００５】
しかしながら、これらの公知方法を実施すると、２次加熱に際し必要以上に温度が高い部分が生じることになった。すなわち、スラブの２次加熱完了時には、図４に示すような表面温度分布となり、図４中「Ａ」で示す範囲の温度が必要以上に上りすぎ、最悪のケースとしてはＡ部が局部溶解を起すトラブルが発生したり、溶解するまでにはいたらなくてもＡ部でスラブ組織が粗大化して、逆に高温による最終製品の磁性劣化が起こるという問題があった。
【０００６】
【発明が解決しようとする課題】
本発明は、かかる事情を鑑み、方向性電磁鋼板の熱間圧延に際して、インヒビタの固溶不足が起きないよう、ガスバーナ加熱炉でのスラブの加熱方法を提供することを目的としている。
【０００７】
【課題を解決するための手段】
前記目的を達成するため、発明者は鋭意検討を行い、１次加熱でスラブ長手方向の温度分布を調整することに着眼した。本発明は、その着眼を具体化するために多くの実験、研究を行った上でなされたものである。すなわち、本発明は、Ｓｉを２％以上含む方向性電磁鋼板製造用スラブを、ガスバーナ加熱炉で１３５０℃以下の温度で１次加熱後、さらに電磁誘導加熱炉で１４００℃〜１４８０℃の温度で加熱してから熱間圧延する方向性電磁鋼板の製造において、
上記ガスバーナ加熱炉内で、スラブの両端より１ｍ以内の範囲を、それ以外の中央部分における長手方向の平均温度より１０℃以上高く加熱し、該中央部分の長手方向各位置の温度を前記平均温度の±１０℃以内に抑制することを特徴とする方向性電磁鋼板用スラブの加熱方法である。この場合、上記スラブの加熱や温度抑制に用いる温度制御手段は、公知のものを使用すれば良い。
【０００８】
【作用】
本発明では、ガスバーナ加熱炉でスラブの両端より１ｍ以内の範囲を、それ以外の中央部分の平均温度よりほぼ１０℃以上高目に過加熱し、さらに該中央部分の長手方向各位置の温度を前記平均温度の±１０℃以内に抑えるようにしたので、電磁誘導加熱炉の出側でスラブの長手方向温度分布は均一になり、インヒビタの再固溶も十分に均一化される。その結果、最終製品の方向性電磁板の磁性劣化が防止できるようになった。以下、図１、図５〜６に基づき、本発明の内容に関して補足説明する。
【０００９】
図１に、本発明を適用して、ガスバーナ加熱炉出口で測定したスラブの温度分布を示す。ＬＥ，ＴＥ両端１ｍ以内のスラブ温度はそれ以外の部分の長手方向の平均温度より１０℃以上高目になっている。その理由は、その後に実施するＩ炉での２次加熱時に、その領域での温度低下がなく、スラブの全長にわたってインヒビタがほぼ完全に再固溶され、端部の磁性劣化を、鉄損値で≦０．００５ｗ／ｋｇ（これ以上鉄損が劣化すると約半数以上のものが１グレートダウンする限界値）に抑制可能となるからである。その様子を図５に示す。なお、図５の縦軸は、スラブ長手方向の中央部分の鉄損値に対するＬＥ端部の鉄損値上昇分を、横軸はスラブ端部の過加熱程度を表わしている。すなわち、図５のグラフは、スラブ端部の過加熱度が１０℃以上あると鉄損上昇が少ないことをあきらかにしている。
【００１０】
次に、両端部より各１ｍの範囲外に相当する中央部分の各位置の加熱温度を中央部分の平均温度の±１０℃以内とするのは、図６に示すように、目標加熱温度から＋１０℃以上外れた過加熱部では、熱間圧延工程の粗圧延時に、結晶粒界割れに起因した表面欠陥の発生率が増加し、逆に−１０℃低温で加熱すると、スラブ段階で粗大析出したインヒビター析出物の再固溶が不十分になり、その部分の磁性が劣化するからである。なお、図６の測定結果は、実線のグラフが目標加熱温度と鉄損の関係を、点線のグラフが目標加熱温度と重度表面欠陥発生率の関係を示す。
【００１１】
【実施例】
Ｃ：０．０５％、Ｓｉ：３．５％、Ｍｎ：０．０８１％、Ｓｅ：０．０２５％、Ｓｂ：０．０３％、Ｎ：２５ｐｐｍ含有した方向性電磁鋼板製造用スラブを、ガスバーナ加熱炉において、図７に示すような長手方向の温度分布になるように、１次加熱した。加熱は、スラブの両端部は加熱炉の灼熱帯において抽出１０分前よりサイドバーナーにて両端部を集中加熱し、図７に示すような温度分布となるようにした。このスラブを、所謂中央部分の平均温度が１２２０℃となる時点で１次加熱を完了し、２次加熱用のＩ炉に装入して１４４０℃まで加熱した。その後、直ちにスラブを抜き出し、熱間圧延を実施した後、ピック→ノルマ処理→１回目冷間圧延→中間焼鈍→２回目冷間圧延→表面洗浄→焼鈍→分離塗布→最終焼鈍→フラットニング（表面コーティング）という通常の電磁鋼板製造工程を経て、板厚が０．２３ｍｍの方向性電磁鋼板を製造した。図８に、その製品の長手方向の鉄損値変化を示すが、製品として好適な絶対値で、且つ均一な分布が得られた。
【００１２】
なお、図８での結果は、局部溶解を抑えるため、スラブ両端部の集中加熱は平均値より１０℃以上５０℃未満だけ高めの温度で行われたものである。
【００１３】
【発明の効果】
以上述べたように、本発明では、方向性電磁鋼板の製造において製品歩留に影響するスラブの磁性劣化を防止するため、熱間圧延前のスラブ加熱に工夫を凝らした。その結果、長手方向で磁性劣化のない製品が得られ、歩留向上に大きな期待が持てるようになった。
【図面の簡単な説明】
【図１】本発明を適用した１次加熱完了時でのスラブ長手方向の温度分布図である。
【図２】従来法によるＩ炉での２次加熱完了時のスラブ長手方向の表面温度分布図である。
【図３】テーパ加熱法により１次加熱したスラブを、Ｉ炉で２次加熱完了した際のスラブ長手方向温度分布図である。
【図４】Ｉ炉で加熱完了時した際のスラブ長手方向の温度分布図である。
【図５】スラブ端部の過加熱レベルとスラブ中央部分鉄損値に対する端部鉄損値の上昇分との関係を表わす図である。
【図６】スラブ中央部分（端部各々１ｍ部を除く部分）の加熱レベル偏差と品質レベルの関係を表わす図である。
【図７】本発明の適用による１次加熱完了時におけるスラブ長手方向の温度分布図である。
【図８】本発明の適用で製造した方向性電磁鋼帯の長手方向での鉄損変化図である。
【符号の説明】
１ スラブ（方向性電磁鋼板製造用）
２ 誘導コイル
３ 電磁誘導炉（Ｉ炉）
４ スラブ両端部とＩ炉の炉端壁との間の空間[0001]
[Industrial application fields]
The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet, and more particularly to a heating technique before hot-rolling the manufacturing slab.
[0002]
[Prior art]
As is well known, the excellent magnetic properties of grain-oriented electrical steel sheets are obtained by selectively developing secondary recrystallized grains having a (100) plane on the plate surface and a <001> axis in the rolling direction by final annealing. It is done. For that purpose, it is important to precipitate fine precipitates called inhibitors, such as MnS, MnSe, AlN, etc. in the steel, and the control of the dispersion form of the inhibitors is performed after these precipitates are once dissolved. , By performing hot rolling.
[0003]
By the way, the slab heating before hot rolling performed for such a purpose is the primary at a temperature of 1350 ° C. or less in a gas burner heating type furnace (hereinafter referred to as “gas furnace”), for example, due to re-solution of the inhibitor component. After heating, an induction heating type furnace (hereinafter referred to as “I furnace”) is a name for standing and heating the slab in the furnace in the so-called I shape with the thickness direction as the bottom. Is equivalent to height.). The secondary heating temperature is 1400 ° C. to 1480 ° C. that enables the inhibitor precipitated coarsely on the slab to be re-dissolved. After the secondary heating, the slab was hot-rolled.
[0004]
In the I furnace stage of the above process, as shown in FIG. 2, the vicinity of both ends in the longitudinal direction of the slab 1 (each referred to as LE and TE ends) has a large radiant heat due to the structure of the furnace. On the other hand, there was a tendency to be 5-30 ° C. lower. Therefore, in the past, the inhibitor was insufficiently re-dissolved in the vicinity of both ends of the slab, and the grain-oriented electrical steel sheet of the final product was likely to have a magnetic failure. As a method for solving this problem, Japanese Patent Application Laid-Open No. 5-59437 discloses that auxiliary heating is performed by arranging an induction heating plate and a heat insulating material in a space 4 formed between the two ends of the I furnace 3 and the slab. The technology is disclosed. JP-A-59-193216 taught a so-called taper heating technique as shown in FIG. 3 with respect to the longitudinal direction of the slab during the primary heating of the gas burner. This is a technique for heating the slab before hot rolling so that the temperature at the rear end in the rolling direction is higher than the front end within a range of 200 ° C.
[0005]
However, when these known methods are carried out, a part where the temperature is higher than necessary is generated during the secondary heating. That is, when the secondary heating of the slab is completed, the surface temperature distribution as shown in FIG. 4 is obtained, the temperature in the range indicated by “A” in FIG. 4 rises more than necessary, and in the worst case, the A part is locally dissolved. There is a problem that the trouble that occurs or the slab structure is coarsened in the part A even if it does not reach melting, and conversely, the magnetic degradation of the final product due to high temperature occurs.
[0006]
[Problems to be solved by the invention]
In view of such circumstances, an object of the present invention is to provide a method for heating a slab in a gas burner heating furnace so that an inhibitor is not sufficiently dissolved during hot rolling of a grain-oriented electrical steel sheet.
[0007]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, the inventor diligently studied and focused on adjusting the temperature distribution in the longitudinal direction of the slab by primary heating. The present invention has been made after many experiments and researches in order to embody the focus. That is, in the present invention, a slab for producing grain-oriented electrical steel sheets containing 2% or more of Si is primarily heated at a temperature of 1350 ° C. or less in a gas burner heating furnace, and further at a temperature of 1400 ° C. to 1480 ° C. in an electromagnetic induction heating furnace. In the production of grain-oriented electrical steel sheet that is hot-rolled after heating,
In the gas burner furnace, a range within 1m from both ends of the slab, higher heating 10 ° C. or higher than the longitudinal average temperature in the central portion of the otherwise the average temperature in the longitudinal direction the temperature of each position of the central portion This is a method for heating a slab for grain-oriented electrical steel sheets, characterized by being controlled within ± 10 ° C. In this case, a well-known thing should just be used for the temperature control means used for the heating of the said slab, or temperature control.
[0008]
[Action]
In the present invention, a gas burner heating furnace is used to overheat a range within 1 m from both ends of the slab at a temperature approximately 10 ° C. higher than the average temperature of the other central portion, and the temperature at each position in the longitudinal direction of the central portion. Since the temperature is kept within ± 10 ° C. of the average temperature, the temperature distribution in the longitudinal direction of the slab becomes uniform on the exit side of the electromagnetic induction heating furnace, and the re-solution of the inhibitor is sufficiently uniformized. As a result, the magnetic deterioration of the directional electromagnetic plate of the final product can be prevented. Hereinafter, a supplementary explanation will be given regarding the contents of the present invention based on FIG. 1 and FIGS.
[0009]
FIG. 1 shows the temperature distribution of a slab measured at the gas burner heating furnace exit by applying the present invention. The slab temperature within 1 m of both ends of LE and TE is higher by 10 ° C. than the average temperature in the longitudinal direction of the other portions. The reason for this is that during the subsequent secondary heating in the I furnace, there is no temperature drop in that region, the inhibitor is almost completely re-dissolved over the entire length of the slab, and the magnetic loss at the end is reduced to the iron loss value. This is because it can be suppressed to ≦ 0.005 w / kg (the limit value at which about half or more of the iron loss deteriorates by 1 when the iron loss is further deteriorated). This is shown in FIG. In addition, the vertical axis | shaft of FIG. 5 represents the iron loss value rise of the LE edge part with respect to the iron loss value of the center part of a slab longitudinal direction, and the horizontal axis represents the overheating degree of a slab edge part. That is, the graph of FIG. 5 reveals that the iron loss increase is small when the degree of overheating at the end of the slab is 10 ° C. or more.
[0010]
Next, as shown in FIG. 6, the heating temperature at each position of the central portion corresponding to outside the range of 1 m from both ends is within ± 10 ° C. of the average temperature of the central portion , as shown in FIG. In the overheated part deviated by ℃ or more, the occurrence rate of surface defects due to grain boundary cracking increased during rough rolling in the hot rolling process. Conversely, when heated at a low temperature of -10 ℃, coarse precipitation occurred in the slab stage. This is because the reprecipitation of the inhibitor precipitate becomes insufficient and the magnetism of the portion is deteriorated. In the measurement results of FIG. 6, the solid line graph shows the relationship between the target heating temperature and the iron loss, and the dotted line graph shows the relationship between the target heating temperature and the incidence of severe surface defects.
[0011]
【Example】
A slab for producing grain-oriented electrical steel sheets containing C: 0.05%, Si: 3.5%, Mn: 0.081%, Se: 0.025%, Sb: 0.03%, N: 25 ppm is used as a gas burner. In the heating furnace, primary heating was performed so as to obtain a temperature distribution in the longitudinal direction as shown in FIG. In the heating, both end portions of the slab were concentratedly heated by a side burner 10 minutes before extraction in the tropical zone of the heating furnace so as to have a temperature distribution as shown in FIG. When the average temperature of the so-called central part reached 1220 ° C., the slab was completed in the primary heating, charged in the I furnace for secondary heating, and heated to 1440 ° C. Then, immediately after extracting the slab and carrying out hot rolling, pick → normalization → first cold rolling → intermediate annealing → second cold rolling → surface cleaning → annealing → separation coating → final annealing → flattening (surface Through a normal electromagnetic steel sheet manufacturing process called coating, a grain-oriented electrical steel sheet having a thickness of 0.23 mm was manufactured. FIG. 8 shows the change in the iron loss value in the longitudinal direction of the product. An absolute value suitable for the product and a uniform distribution were obtained.
[0012]
In addition, the result in FIG. 8 shows that concentrated heating at both ends of the slab was performed at a temperature higher than the average value by 10 ° C. or more and less than 50 ° C. in order to suppress local melting.
[0013]
【The invention's effect】
As described above, in the present invention, in order to prevent the magnetic deterioration of the slab which affects the product yield in the production of the grain-oriented electrical steel sheet, the slab heating before hot rolling has been devised. As a result, a product having no magnetic deterioration in the longitudinal direction was obtained, and great expectation was obtained for yield improvement.
[Brief description of the drawings]
FIG. 1 is a temperature distribution diagram in the longitudinal direction of a slab when primary heating to which the present invention is applied is completed.
FIG. 2 is a surface temperature distribution diagram in the longitudinal direction of a slab when secondary heating is completed in an I furnace according to a conventional method.
FIG. 3 is a temperature distribution diagram in the longitudinal direction of the slab when the secondary heating is completed in the I furnace for the primary heating by the taper heating method.
FIG. 4 is a temperature distribution diagram in the longitudinal direction of the slab when heating is completed in the I furnace.
FIG. 5 is a diagram showing the relationship between the overheating level at the end of the slab and the increase in the end iron loss value relative to the slab center partial iron loss value.
FIG. 6 is a diagram illustrating a relationship between a heating level deviation and a quality level of a slab center part (a part excluding 1 m part at each end).
FIG. 7 is a temperature distribution diagram in the longitudinal direction of the slab when primary heating is completed according to the application of the present invention.
FIG. 8 is a change diagram of iron loss in the longitudinal direction of a directional electromagnetic steel strip manufactured by application of the present invention.
[Explanation of symbols]
1 Slab (for producing grain-oriented electrical steel sheets)
2 Induction coil 3 Electromagnetic induction furnace (I furnace)
4 Space between both ends of slab and furnace end wall of I furnace

Claims (1)

Ｓｉを２％以上含む方向性電磁鋼板製造用スラブを、ガスバーナ加熱炉で１３５０℃以下の温度で１次加熱後、さらに電磁誘導加熱炉で１４００℃〜１４８０℃の温度で加熱してから熱間圧延する方向性電磁鋼板の製造において、
上記ガスバーナ加熱炉内で、スラブの両端より１ｍ以内の範囲を、それ以外の中央部分における長手方向の平均温度より１０℃以上高く加熱し、該中央部分の長手方向各位置の温度を前記平均温度の±１０℃以内に抑制することを特徴とする方向性電磁鋼板用スラブの加熱方法。A slab for producing grain-oriented electrical steel sheets containing 2% or more of Si is first heated in a gas burner heating furnace at a temperature of 1350 ° C. or lower, and further heated in an electromagnetic induction heating furnace at a temperature of 1400 ° C. to 1480 ° C. In the production of the grain-oriented electrical steel sheet to be rolled,
In the gas burner furnace, a range within 1m from both ends of the slab, higher heating 10 ° C. or higher than the longitudinal average temperature in the central portion of the otherwise the average temperature in the longitudinal direction the temperature of each position of the central portion A method for heating a slab for grain-oriented electrical steel sheets, characterized by being controlled within ± 10 ° C.

Images