【発明の詳細な説明】[Detailed description of the invention]
（産業上の利用分野）
本発明は極めて均一性に富んだ絶縁皮膜と優れ
た磁気特性を得ることのできる方向性電磁鋼板の
脱炭焼鈍方法に関する。
（従来の技術）
方向性電磁鋼板の製造工程においては鋼中のＣ
量の所定量の存在は鋼の金属組織のコントロール
に重要な役割があるため通常0.02〜0.07％を含有
させて鋳込まれる。しかし製品に存在するＣ量は
磁気特性を著しく劣化させるので最終仕上焼鈍前
に0.0030％程度以下にまで減少させる脱炭焼鈍工
程を有しているのが普通である。
この脱炭焼鈍工程は鋼中のＣを鋼板表面に拡散
させ雰囲気中の酸素と結合させ一酸化炭素として
除外する機構からなる。しかし、この脱炭焼鈍工
程では脱炭のみならず後の仕上焼鈍工程でのグラ
ス皮膜形成に重要なSiO2及びフアイヤライト
（Fayalite 2FeO・SiO2）主体の酸化膜の形成と
いう重要な役割があるため雰囲気中の酸化量のコ
ントロールが重要である。
通常は水素或いは水素＋窒素を主体とする混合
ガスを所定温度の水中に通すなどして所定露点を
確保して露点をコントロールすることが多い。こ
の酸化量の表示としての露点は雰囲気ガス中の水
素ガス量により実質内容が異なるので一般には
PH20／PH2値を酸化度として表示する。
従来の方向性電磁鋼板の脱炭焼鈍工程は雰囲気
の酸化度をPH20／PH2値として約0.15〜0.75の範囲
内の一定値とされるのが普通であつた。その後検
討され特公昭57−1575号公報記載の方法では、脱
炭焼鈍工程を前部と後部に分け、脱炭焼鈍温度、
例えば750〜880℃での前部領域の雰囲気の酸化度
PH20／PH2を0.15以上とし、後部領域の雰囲気の
酸化度PH20／PH2を0.75以下でかつ前部領域の酸
化度PH20／PH2より小さくする方法が提案されて
いる。この脱炭焼鈍工程において前部と後部に分
け、後部の雰囲気の酸化度と前部より小さくする
ことにより、製品の磁気特性と皮膜特性が改善さ
れるという作用効果があり有用である。
（発明が解決しようとする問題点）
ところで本発明者らは、時代の要請である省エ
ネルギーに対処すべく、方向性電磁鋼板の磁気特
性、皮膜特性ともされに改善し、かつより安定し
た製品が製造されるように脱炭焼鈍工程について
検討した。
（問題点を解決するための手段）
その結果、これまでは脱炭焼鈍に際して均熱後
の冷却帯の雰囲気には着目されていなかつたもの
をこの冷却帯における750℃以下の雰囲気の酸化
度PH20／PH2を0.008以下にすると、鋼板は追加酸
化されることがなく脱炭焼鈍温度つまり均熱帯で
形成されたフアイライト（Fayalite）層の一部が
シリカ（Silica）層に変化する反応があつて鋼板
表面の酸化膜層中のFe酸化物を低減しSiO2比率
を高め、SiO2主体の緻密な酸化膜層が形成され、
製品の磁気特性、皮膜特性がともに改善されるこ
とを見出した。
以下に本発明を詳細に述べる。
通常、脱炭焼鈍工程においては鋼板の脱炭性及
び酸化膜形成の点から脱炭焼鈍時の昇温中及び均
熱時の雰囲気ガス、その流量、酸化度、均熱温度
と時間等のコントロールは重要であり種々検討さ
れて来た。
近年では方向性電磁鋼板は高Si化に伴つて２次
再結晶の安定化等の目的で鋼成分としてSb、Cu、
Sn、Mo等の種々の元素がインヒビターとしてあ
るいはインヒビター強化の目的で添加されてい
る。これらの微量の添加元素は何れも脱炭性を阻
害する傾向がある。雰囲気の酸化度、脱炭温度、
時間等の通板条件は重要であり脱炭反応と酸化膜
形成の主反応域である脱炭焼鈍炉での鋼板の昇温
および均熱過程については充分な検討がなされて
来たが、均熱終了後の冷却帯の雰囲気条件につい
ては従来あまり検討がなされていなかつた。この
ため脱炭焼鈍工程での昇温過程、均熱過程の雰囲
気条件を充分管理してもガラス皮膜形成及び磁性
が変動することが多かつた。
この原因について検討したところ、脱炭焼鈍炉
内の冷却帯の雰囲気の変動が原因していることが
判つた。そこで冷却帯での鋼板温度と雰囲気ガス
の酸化度との関係について種々検討した。これを
実験データを参照して述べる。
供試材としてＣ：0.073％、Si：3.30％、Mn：
0.075％、Ｓ：0.024％、Al：0.026％、Ｎ：0.008
％をベース成分とするスラブを、公知の方法によ
り、熱間圧延→熱延板焼鈍→冷間圧延して0.225
mm厚とした鋼板を用いた。
この鋼板をN2：50％＋H2：50％、酸化度
PH20／PH20.52の雰囲気ガス中で840℃×２分間脱
炭焼鈍し、この脱炭焼鈍の冷却帯にて750℃から
200℃以下に冷却するさいの雰囲気ガスの酸化度
PH20／PH2を0.001〜0.5に変えて通板した。
この脱炭焼鈍後の鋼板にMg100重量部にTiO2
を３重量部配合した焼鈍分離剤を塗布し、1200℃
で20時間の最終仕上焼鈍を行なつた。
この鋼板の鉄損値W17/50を測定し、その結果を
第１図に示す。この図から明らかなように、鉄損
値に冷却過程の雰囲気ガスの酸化度PH20／PH2が
大きな影響を及ぼし、該酸化度PH20／PH2を0.008
以下に低減して冷却すると鉄損値が大幅に改善さ
れて低く、その値も変動が少なく安定することが
見出された。この図には示していないが、酸化度
PH20／PH2を0.008以下で冷却すると、皮膜特性が
格段に優れ、金属光沢斑点模様、ガスマーク状な
どが全くなくて全板幅にわたつて外観及び密着性
とも極めて優れている。
本発明が適用される方向性電磁鋼板の鋼成分は
特別な規制は必要ではなく、Ｃ：0.02〜0.10％、
Si：2.5〜4.0％にインヒビターを形成するMn、
Ｓ、Al、ＮやCu、Sn、Se、Sb等を１種または２
種以上が含まれうるものである。
またスラブの熱間圧延に先立つ加熱温度や、熱
間圧延の条件、熱延板焼鈍の条件、冷間圧延条件
は公知のものでよい。さらに１回冷間圧延または
中間焼鈍をはさんで２回以上の冷間圧延により最
終板厚とする方法であつてもよい。
次いで行なう脱炭焼鈍は公知の温度範囲、例え
ば850℃以上で２分間以上行なわれ、該脱炭焼鈍
の冷却過程では750℃以下を雰囲気ガスの酸化度
PH20／PH2を0.008以下として冷却する。
冷却帯雰囲気酸化度を750℃以下の温度で
PH20／PH2≦0.008に規定した理由はPH20／PH2が
0.008超ではフアイライト（Fayalite）或いはウ
スタイト（Wustite）形成域であり鋼板酸化膜層
の変質、追加酸化の影響で酸化膜中のFe酸化物
量を増大してグラス皮膜形成条件にバラツキをも
たらし、極端な場合には仕上焼鈍でのコイルラツ
プ間雰囲気の酸化度を高めるのと同じ悪影響によ
り金属斑点模様等の皮膜欠陥を生じる。このよう
な欠陥の発生を完全に防止し、外観及び密着性と
もに優れた皮膜を得るには酸化度PH20／PH2を
0.008以下とする必要がある。また当該酸化度以
下にて冷却すると、酸化膜層はSiO2主体の緻密
なものとなり、次工程の仕上焼鈍の昇温時にイン
ヒビターの変質分解等が防止され、２次再結晶が
高度に安定し磁気特性も優れる。
冷却過程において雰囲気酸化度を規定する温度
を750℃以下とするのは750℃超では脱炭及び酸化
膜形成がさかんな温度域であるのに対し、これ以
下では段階的ではあるが脱炭及び酸化膜形成反応
が弱まり有効な温度域とならないからである。
脱炭焼鈍の後は、MgOを主成分としTiO2等の
Ti酸化物やアンチモンやSrS等の硫化物等の１種
または２種以上が配合された焼鈍分離剤が鋼板に
塗布され、次いで仕上焼鈍される。
本発明によると、脱炭焼鈍工程での冷却帯で鋼
板の追加酸化が生じない上に均熱過程で形成され
たフアイヤライトの一部がシリカ層に変化する反
応が起つて鋼板表面の酸化膜層中のSiO2比率が
高くなりSiO2主体の緻密な酸化膜層となる。こ
のため仕上焼鈍昇温過程でのコイルラツプ間の露
点を下げ、雰囲気ガスによる酸化、還元反応を受
け難くし、脱炭焼鈍時に形成したSiO2主体の酸
化膜は変質することなくグラス皮膜形成反応が生
じ良質のガラス皮膜を形成する。
又このSiO2主体の酸化膜は仕上焼鈍昇温過程
での雰囲気ガスによるインヒビターの変質、分離
等からの保護作用があるため２次再結晶を安定化
し、磁性も向上するものと思われる。
（実施例）
次に実施例を示す。
実施例 １
Ｃ：0.068％、Si：3.15％、Mn：0.070％、Al：
0.026％、Cu：0.08％、Sn：0.10％、Ｎ：0.008％、
Ｓ：0.025％のスラブを公知の方法により熱間圧
延−熱延板焼鈍−冷間圧延により0.29mmの鋼板と
した。
この鋼板を連続焼鈍炉で840℃にてN225％＋
H275％、PH20／PH2＝0.52の雰囲気ガスで２分間
脱炭焼鈍後、冷却帯における750℃からの冷却を
雰囲気ガスN225％＋H275％でPH20／PH2を0.5、
0.2、0.08、0.008、0.001にて行つた。このときの
冷却帯750〜200℃までの冷却帯通過時間は60秒で
あつた。
この脱炭焼鈍後の鋼板MgO100重量部にTiO25
重量部を配合した焼鈍分離剤を塗布後、1200℃、
20時間の最終仕上焼鈍を行つた。このときの鋼板
表面の酸化膜の酸素量及び磁性、皮膜特性の測定
結果を第１表に示す。
(Field of Industrial Application) The present invention relates to a method for decarburizing annealing grain-oriented electrical steel sheets, which allows obtaining an extremely uniform insulating film and excellent magnetic properties. (Prior art) In the manufacturing process of grain-oriented electrical steel sheets, carbon in steel is
Since the presence of a predetermined amount plays an important role in controlling the metal structure of steel, it is usually cast with a content of 0.02 to 0.07%. However, since the amount of C present in the product significantly deteriorates the magnetic properties, it is common to have a decarburization annealing step to reduce the amount to about 0.0030% or less before final annealing. This decarburization annealing process consists of a mechanism in which carbon in the steel is diffused onto the surface of the steel sheet, combined with oxygen in the atmosphere, and removed as carbon monoxide. However, this decarburization annealing process plays an important role not only in decarburization but also in forming an oxide film mainly composed of SiO 2 and Fayalite (Fayalite 2FeO SiO 2 ), which is important for the formation of a glass film in the final annealing process. Controlling the amount of oxidation in the atmosphere is important. Usually, the dew point is often controlled by passing hydrogen or a mixed gas mainly consisting of hydrogen and nitrogen through water at a predetermined temperature to ensure a predetermined dew point. The dew point, which is an indication of the amount of oxidation, differs in actual content depending on the amount of hydrogen gas in the atmosphere, so it is generally not used.
Displays the P H20 /P H2 value as the degree of oxidation. In the conventional decarburization annealing process for grain-oriented electrical steel sheets, the oxidation degree of the atmosphere was usually set to a constant value within the range of about 0.15 to 0.75, expressed as the P H20 /P H2 value. After that, the method described in Japanese Patent Publication No. 57-1575 divided the decarburization annealing process into a front part and a rear part, and the decarburization annealing temperature,
Oxidation degree of the atmosphere in the front area, for example at 750-880℃
A method has been proposed in which P H20 /P H2 is set to 0.15 or more, and the oxidation degree P H20 /P H2 of the atmosphere in the rear region is set to 0.75 or less and smaller than the oxidation degree P H20 /P H2 of the front region. This decarburization annealing step is divided into a front part and a rear part, and by making the oxidation degree of the atmosphere in the rear part lower than that in the front part, the magnetic properties and film properties of the product are improved, which is useful. (Problems to be Solved by the Invention) In order to meet the demands of the times for energy conservation, the present inventors have improved the magnetic properties and film properties of grain-oriented electrical steel sheets, and created a more stable product. The decarburization annealing process was investigated as manufactured. (Means for solving the problem) As a result, the oxidation degree P When H20 /P H2 is set to 0.008 or less, the steel plate will not undergo additional oxidation, and a reaction occurs in which part of the Fayalite layer formed at the decarburization annealing temperature, that is, the soaking zone, changes into a silica layer. This reduces Fe oxide in the oxide film layer on the surface of the steel sheet and increases the SiO 2 ratio, forming a dense oxide film layer mainly composed of SiO 2 .
It was found that both the magnetic properties and film properties of the product were improved. The present invention will be described in detail below. Normally, in the decarburization annealing process, the atmospheric gas, its flow rate, degree of oxidation, soaking temperature and time are controlled during heating and soaking during decarburization annealing from the viewpoint of decarburization properties and oxide film formation of the steel sheet. is important and has been studied in various ways. In recent years, as grain-oriented electrical steel sheets have become more Si-rich, Sb, Cu, and
Various elements such as Sn and Mo are added as inhibitors or for the purpose of strengthening the inhibitor. All of these trace amounts of added elements tend to inhibit decarburization. oxidation degree of the atmosphere, decarburization temperature,
Threading conditions such as running time are important, and sufficient studies have been conducted on the heating and soaking process of steel sheets in the decarburization annealing furnace, which is the main reaction area for decarburization and oxide film formation. In the past, little consideration has been given to the atmospheric conditions in the cooling zone after heating has ended. For this reason, even if the atmospheric conditions during the temperature raising process and soaking process in the decarburization annealing process were well controlled, the glass film formation and magnetism often fluctuated. When we investigated the cause of this, we found that it was caused by changes in the atmosphere in the cooling zone in the decarburization annealing furnace. Therefore, various studies were conducted on the relationship between the steel plate temperature in the cooling zone and the oxidation degree of the atmospheric gas. This will be explained with reference to experimental data. Sample materials: C: 0.073%, Si: 3.30%, Mn:
0.075%, S: 0.024%, Al: 0.026%, N: 0.008
A slab having a base component of 0.225
A steel plate with a thickness of mm was used. This steel plate was treated with N 2 : 50% + H 2 : 50%, oxidation degree
Decarburization annealing is performed at 840℃ for 2 minutes in an atmospheric gas of P H20 /P H2 0.52, and the temperature is reduced from 750℃ in the cooling zone of this decarburization annealing.
Oxidation degree of atmospheric gas when cooling to below 200℃
Threading was carried out by changing P H20 /P H2 from 0.001 to 0.5. After decarburization annealing, 100 parts by weight of Mg and TiO 2 were added to the steel sheet.
Apply an annealing separator containing 3 parts by weight of
Final annealing was carried out for 20 hours. The iron loss value W 17/50 of this steel plate was measured, and the results are shown in Figure 1. As is clear from this figure, the oxidation degree P H20 /P H2 of the atmospheric gas during the cooling process has a large effect on the iron loss value, and the oxidation degree P H20 /P H2 is 0.008.
It has been found that when the iron loss is reduced to below and cooled, the iron loss value is significantly improved and lowered, and the value is also stable with little fluctuation. Although not shown in this diagram, the degree of oxidation
When P H20 /P H2 is cooled to 0.008 or less, the film properties are extremely excellent, with no metallic luster spots or gas marks, and the appearance and adhesion are excellent over the entire width of the plate. No special regulations are required for the steel composition of grain-oriented electrical steel sheets to which the present invention is applied; C: 0.02 to 0.10%;
Si: 2.5-4.0% Mn, forming an inhibitor
One or two types of S, Al, N, Cu, Sn, Se, Sb, etc.
It can include more than one species. Further, the heating temperature prior to hot rolling of the slab, hot rolling conditions, hot rolled sheet annealing conditions, and cold rolling conditions may be any known ones. Furthermore, the final plate thickness may be obtained by performing one cold rolling or two or more cold rolling with intermediate annealing in between. The subsequent decarburization annealing is carried out at a known temperature range, for example, 850°C or higher for 2 minutes or more, and in the cooling process of the decarburization annealing, the temperature is 750°C or lower depending on the oxidation degree of the atmospheric gas.
Cool with P H20 /P H2 of 0.008 or less. Cooling zone atmosphere oxidation degree at temperature below 750℃
The reason for specifying P H20 /P H2 ≦0.008 is that P H20 /P H2 is
If it exceeds 0.008, it is a Fayalite or Wustite formation region, and the steel sheet oxide film layer is altered, and the amount of Fe oxide in the oxide film increases due to the effect of additional oxidation, causing variations in the glass film formation conditions, resulting in extreme In some cases, film defects such as metal speckles occur due to the same negative effect as increasing the degree of oxidation in the atmosphere between the coil wraps during final annealing. In order to completely prevent the occurrence of such defects and obtain a film with excellent appearance and adhesion, the oxidation degree P H20 /P H2 should be adjusted.
Must be 0.008 or less. In addition, when cooled below the oxidation level, the oxide film layer becomes dense and mainly composed of SiO 2 , which prevents the inhibitor from degrading and decomposing when the temperature is raised in the final annealing process in the next step, and makes secondary recrystallization highly stable. It also has excellent magnetic properties. The temperature that defines the degree of atmospheric oxidation in the cooling process is set to 750°C or less. Above 750°C, decarburization and oxide film formation occur rapidly, whereas below this temperature, decarburization and oxide film formation occur, albeit in stages. This is because the oxide film forming reaction is weakened and the temperature range is not effective. After decarburization annealing, MgO is the main component and TiO2 etc.
An annealing separator containing one or more of Ti oxide and sulfides such as antimony and SrS is applied to the steel sheet, and then finish annealing is performed. According to the present invention, additional oxidation of the steel plate does not occur in the cooling zone during the decarburization annealing process, and a reaction occurs in which part of the fireite formed during the soaking process changes into a silica layer, resulting in an oxide film layer on the surface of the steel plate. The SiO 2 ratio inside increases, resulting in a dense oxide film layer consisting mainly of SiO 2 . For this reason, the dew point between the coil wraps during the final annealing temperature rise process is lowered, making it less susceptible to oxidation and reduction reactions due to atmospheric gas, and the SiO 2 -based oxide film formed during decarburization annealing is not altered and the glass film formation reaction is carried out. forms a high-quality glass film. In addition, this SiO 2 -based oxide film has a protective effect against deterioration and separation of the inhibitor due to atmospheric gas during the final annealing temperature raising process, so it is thought to stabilize secondary recrystallization and improve magnetism. (Example) Next, an example will be shown. Example 1 C: 0.068%, Si: 3.15%, Mn: 0.070%, Al:
0.026%, Cu: 0.08%, Sn: 0.10%, N: 0.008%,
A slab containing S: 0.025% was hot rolled, hot rolled plate annealed, and cold rolled into a 0.29 mm steel plate using a known method. This steel plate was heated in a continuous annealing furnace at 840°C with 25% N 2 +
After decarburizing annealing for 2 minutes in an atmospheric gas of H 2 75% and P H20 /P H2 = 0.52, cooling from 750°C in a cooling zone to 0.5 P H20 /P H2 with an atmospheric gas of N 2 25% + H 2 75%. ,
I did it at 0.2, 0.08, 0.008, and 0.001. At this time, the cooling zone passage time from 750 to 200°C was 60 seconds. TiO 2 5 is added to 100 parts by weight of MgO in this steel sheet after decarburization annealing.
After applying an annealing separator containing parts by weight, 1200℃,
Final annealing was performed for 20 hours. Table 1 shows the measurement results of the oxygen content, magnetism, and film characteristics of the oxide film on the surface of the steel sheet at this time.
【表】【table】
【表】
実施例 ２
Ｃ：0.075％、Si：3.25％、Mn：0.072％、Al：
0.027％、Cu：0.09％、Sn：0.10％、Ｎ：0.008％、
Ｓ：0.025％のスラブを公知の方法により熱間圧
延−熱延板焼鈍−冷間圧延により0.225mm板厚の
鋼板とした。
この鋼板を連続焼鈍炉中で840℃にて雰囲気ガ
スN225％＋H275％、PH20／PH2＝0.52で２分間脱
炭焼鈍後、冷却帯において750℃から200℃以下に
冷却するさい温度の降下につれてN2とH2の混合
されてなる雰囲気のN2の割合を25％から80％に
増加させた雰囲気ガスにて酸化度PH20／PH2を
0.5、0.2、0.08、0.008、0.001として冷却した。
このときの冷却帯750〜200℃までの通過時間は
60秒であつた。この脱炭焼鈍後の鋼板に実施例１
と同様に焼鈍分離剤を塗布し、最終仕上焼鈍を行
つた。かくして得られた鋼板表面の酸化膜の酸素
量、磁気特性、皮膜特性を第２表に示す。[Table] Example 2 C: 0.075%, Si: 3.25%, Mn: 0.072%, Al:
0.027%, Cu: 0.09%, Sn: 0.10%, N: 0.008%,
A slab containing S: 0.025% was hot rolled, hot-rolled plate annealed, and cold-rolled into a steel plate having a thickness of 0.225 mm using a known method. This steel plate is decarburized and annealed for 2 minutes at 840°C in a continuous annealing furnace with an atmospheric gas of 25% N 2 + 75% H 2 and P H20 /P H2 = 0.52, and then cooled from 750°C to below 200°C in a cooling zone. As the temperature decreases, the oxidation degree P H20 /P H2 is increased using an atmosphere gas in which the proportion of N 2 in the mixed atmosphere of N 2 and H 2 is increased from 25% to 80%.
Cooled as 0.5, 0.2, 0.08, 0.008, 0.001. At this time, the passage time from 750 to 200℃ in the cooling zone is
It was hot in 60 seconds. Example 1 to this steel plate after decarburization annealing
In the same manner as above, an annealing separator was applied and final annealing was performed. Table 2 shows the oxygen content, magnetic properties, and film properties of the oxide film on the surface of the steel sheet thus obtained.
【表】
実施例 ３
Ｃ：0.048％、Si：3.18％、Mn：0.068％、Al：
0.010％、Ｓ：0.024％を含有するスラブを公知の
方法により熱延した。これを酸洗後0.68mmまで冷
間圧延し、980℃で中間焼鈍を行つた後、最終板
厚0.27mmまで冷間圧延した。
次いで脱炭焼鈍を連続炉中で実施例１と同様に
して行い、冷却帯における雰囲気の酸化度PH20／
PH2を変えて冷却した。
この脱炭焼鈍後の鋼板に焼鈍分離剤として
MgO100重量部に対しTiO21重量部を添加して塗
布し、1200℃×20hrの最終仕上焼鈍を行つた。こ
のときの磁気特性、皮膜特性を第３表に示す。[Table] Example 3 C: 0.048%, Si: 3.18%, Mn: 0.068%, Al:
A slab containing S: 0.010% and S: 0.024% was hot rolled by a known method. After pickling, this was cold rolled to a thickness of 0.68 mm, intermediately annealed at 980°C, and then cold rolled to a final thickness of 0.27 mm. Next, decarburization annealing was performed in a continuous furnace in the same manner as in Example 1, and the oxidation degree of the atmosphere in the cooling zone was reduced to P H20 /
It was cooled by changing the P H2 . As an annealing separator for this steel plate after decarburization annealing.
1 part by weight of TiO 2 was added to 100 parts by weight of MgO, and final annealing was performed at 1200°C for 20 hours. The magnetic properties and film properties at this time are shown in Table 3.
【表】
以上のように、本発明によると磁気特性がすぐ
れ、皮膜特性にもすぐれた方向性電磁鋼板が製造
される。[Table] As described above, according to the present invention, grain-oriented electrical steel sheets with excellent magnetic properties and excellent film properties are manufactured.
【図面の簡単な説明】[Brief explanation of drawings]
第１図は本発明における鉄損値W17/50に及ぼす
脱炭焼鈍の冷却過程における雰囲気ガスの酸化度
PH20／PH2の影響を示す図である。
Figure 1 shows the effect of the oxidation degree of atmospheric gas in the cooling process of decarburization annealing on the iron loss value W 17/50 in the present invention.
FIG. 3 is a diagram showing the influence of P H20 /P H2 .