JP4473357B2 - Method for producing unidirectional electrical steel sheet with excellent magnetic properties - Google Patents

Description

次いで、この熱延板を表２に示す条件で焼鈍した。鋼板の焼鈍を２段サイクルとし、高温側を１１２０℃×３０秒均熱した後、低温側温度を９５０〜６００℃とし、高温側から低温側へ移行する過程の９８０℃〜９２０℃の滞留時間（秒）を測定した。
【００１６】
【表２】

この後酸洗し、冷延して板厚：０．２３ｍｍとした。次いで脱炭焼鈍を８４０℃の温度でＮ₂ ：２５％、Ｈ₂ ：７５％、露点６８℃の雰囲気中で行った。次いで、７５０℃×３０秒の窒化処理をＮ₂ 、Ｈ₂ 、ＮＨ₃ の混合ガス中で行い、窒化後の鋼板の窒素量を２２０ｐｐｍに調整した。この後、ＭｇＯとＴｉＯ₂ を主成分とする焼鈍分離剤を塗布し、１２００℃×２０時間の仕上げ焼鈍を行った。
【００１７】
図１にＡｌＮ−熱延板焼鈍条件−磁束密度（Ｂ８）の関係を示す。この図から高磁束密度が得られる９８０℃〜９２０℃の滞留時間ｔ（秒）とＡｌR の関係は、
３．１４−０．０１５８×ＡｌR ≦ｌｏｇｔ≦３．８５−０．１５８×ＡｌR 、ｔ≧１０ｓｅｃ
であることが分かる。
【００１８】
次に、表１に示すインゴットＮｏ．５の熱延板を用いて、高温側温度の影響を検討した。熱延板焼鈍は表３の条件で行った。高温側から低温側へ移行する過程の９８０℃〜９２０℃の滞留時間はいずれも上記の関係を満足するように調整した。
【００１９】
【表３】

この後の処理条件は前述したものと同じにした。この結果を図２に示す。
【００２０】
図２からＢ8 ：１．９３Ｔ以上得られる高温側の温度は１０６０℃〜１１７０℃の範囲である。
このような焼鈍で高Ｂ8 が得られる理由についてはまだ明確にはされていないが、現在のところ次のように考えている。二次再結晶の方位を含めて二次再結晶現象に影響する因子としては一次再結晶組織（平均粒径，粒径分布）、集合組織、インヒビター強度等がある。一次再結晶完了後粒成長に伴って集合組織、粒径分布に変化が生じる。二次再結晶の核化、粒成長を容易にするためには一次再結晶組織として粒径は均一であり一定の大きさ以上であることが望ましい。
【００２１】
一方、集合組織は二次再結晶する方位粒（｛１１０｝＜００１＞方位等）と二次再結晶粒を成長させ易い方位粒（｛１１１｝＜１１２＞方位等）を適当量得ることが必要である。これには圧延率の他に冷間圧延する前の鋼板の結晶粒径（再結晶率）及び変態相の量、固溶Ｃ等が影響する。
本発明のプロセスにおいて、冷間圧延以前にインヒビターが存在する事は一次再結晶組織の調整を困難にするため好ましくないが、素材成分にＡｌ，Ｎを用いるかぎり、ＡｌＮの析出は避けられない。特に微細析出物のコントロールが重要である。この析出サイズは焼鈍条件が同一ならＡｌR が小さいもの程小さく、一次再結晶粒粒成長抑制力は大きい。
【００２２】
工場出鋼の電磁鋼のＡｌ，Ｎ等は一定の範囲のバラツキ有しているため、同一温度で脱炭焼鈍すると一次再結晶粒径に差が生じ磁気特性が変動する。このため、脱炭焼鈍温度を調節して特性の高位安定化を図る必要がある。ところが、脱炭焼鈍温度を変更すると酸化層の質、量が変わり良好なフォルステライト被膜形成に支障を来すことになる。
【００２３】
本発明は、この成分変動から起こる一次再結晶粒径変動を小さくし、脱炭焼鈍温度の変更を極力抑えることによって磁気特性の優れた一方向性電磁鋼板を安定して製造するものである。熱延板焼鈍の高温側から低温側へ移行する過程の９８０℃〜９２０℃の滞留時間を変えることで、ＡｌR のバラツキによる一次再結晶粒径の変動を小さくする理由については次のように考えている。
【００２４】
熱延板焼鈍を２段サイクルとする場合、ＡｌＮの析出ノーズ域は９２０〜９８０℃の範囲にあり、この温度域の滞留時間の長、短で析出が左右されると考えられる。従って、析出物が成長し易いＡｌR 値の大きい材料は低温側保定温度を低くして、析出ノーズ域の滞留時間を短くして析出を抑制し、一方、ＡｌR 値の小さい材料は長めにして析出を促進させることによってインヒビター効果をコントロールしているものと考えている。析出ノーズ域の通過時間が短い場合、一部は脱炭焼鈍時により微細に析出するため、一次再結晶粒成長の抑制作用は大きい。
【００２５】
次に、出発材料とする電磁鋼スラブの成分組成の限定理由を説明する。
Ｃは、その含有量が０．０２５％未満になると二次再結晶が不安定になり且つ、二次再結晶した場合でも製品の磁束密度（Ｂ8 値）が１．８０Ｔに満たない低いものとなる。一方、０．０７５％を超えると脱炭焼鈍時間が長大なものとなり、生産性を著しく損なう。
【００２６】
Ｓｉは、その含有量が２．５％未満になると低鉄損の製品を得難く、一方、Ｓｉの含有量が４．５％を超えて多くなりすぎると材料の冷間圧延時に、割れ、破断が多発し，安定した冷間圧延作業を不可能にする。
本発明の出発材料の成分系における特徴の１つは、Ｓを０．０１５％以下とすることにある。従来、公知の技術、例えば特公昭４０−１５６４４号広報或いは特公昭４７−２５２５０号広報に開示されている技術においては、Ｓは二次再結晶を生起させるに必要な析出物であるＭｎＳの形成元素として必須であった。前記公知技術において、Ｓが最も効果を発揮する含有量範囲があり、それは熱間圧延に先立って行われるスラブの加熱段階でＭｎＳを固溶できる量として規定されていた。しかしながら、インヒビターとして（Ａｌ，Ｓｉ）Ｎを用いる本発明においてはＭｎＳは特に必要としない。むしろ、ＭｎＳが増加することは磁気特性上好ましくない。従って、本発明においては、Ｓの含有量は０．０１５％以下とする。
【００２７】
Ａｌは、Ｎと結合してＡｌＮを形成するが、本発明においては後工程即ち一次再結晶完了後に鋼を窒化することにより、（Ａｌ，Ｓｉ）Ｎを形成せしめることを必須としているから、フリーのＡｌが一定量以上必要である。そのため、酸可溶性Ａｌとして，０．０１５〜０．０４０％添加する。
Ｎは、０．０１０％以下にする必要がある。これを超えるとブリスターと呼ばれる鋼板表面の膨れが発生する。また一次再結晶組織の調整が困難になる。下限は０．００２０％とする。この値未満になると二次再結晶粒を発達させるのが困難になる。
【００２８】
Ｍｎは、含有量が少なすぎると二次再結晶が不安定となり、一方、多すぎると高い磁束密度をもつ製品を得難くなる。適正な含有量は０．０５０〜０．４５％である。
ＳｎとＣｒは、必要に応じて複合添加で仕上げ焼鈍後の被膜形成を安定化すると同時に、ＳｎおよびＣｒは脱炭焼鈍後の集合組織を改善し、ひいては二次再結晶粒を小粒化し被膜の安定化と相俟って鉄損改善に効果が大きく、Ｓｎの適量は０．０２〜０．１５％でありこれより少ないと効果が弱く、一方、多いと窒化困難になり二次再結晶粒が発達しなくなる。また、Ｃｒの適量は０．０５〜０．１５％が良い。
【００２９】
Ｃｕは、０．０２〜０．３０％が適量であり、この範囲において磁束密度が向上する。
なお、微量のＰ，Ｔｉを鋼中に含有せしめることは、本発明の趣旨を損なうものではない。
次に、本発明の製造プロセスについて説明する。
【００３０】
電磁鋼スラブは転炉或いは電気炉等の溶解炉で鋼を溶製し、必要に応じて真空脱ガス処理し、次いで連続鋳造によって或いは造塊後分塊圧延することによって得られる。
然る後、熱間圧延に先立つスラブ加熱がなされる。本発明のプロセスにおいては、スラブ加熱温度は１２８０℃以下の低いものとして加熱エネルギーの消費量を少なくするとともに、鋼中のＡｌＮを完全には固溶させずに不完全固溶状態とする。また、さらに固溶温度の高いＭｎＳは、上記スラブ加熱温度では当然のことながら不完全固溶状態となる。このスラブを熱延して所定の厚みの熱延板を造る。
【００３１】
熱延板は引き続き焼鈍と１回の冷間圧延、もしくは中間焼鈍を介挿する２回以上の圧延を施して最終板厚とされる。この時の仕上冷間圧延は高いＢ8 値を得るために８０％以上とされる。この最終圧延に先立つ熱延板焼鈍もしくは中間焼鈍の条件として、既に述べたように、その高温側から低温側へ移行する途中の９８０℃〜９２０℃の滞留時間ｔ（秒）とＡｌR の関係を、
３．１４−０．０１５８×ＡｌR ≦ ｌｏｇｔ ≦ ３．８５−０．１５８×ＡｌR 、
ｔ≧１０ｓｅｃ
に調整することが必要である。
【００３２】
焼鈍時間については種種検討した結果、高温側の均熱時間は１８０秒以内が良い。低温側の温度は９８０〜９２０℃の滞留時間を確保するため、７００〜９８０℃にする必要がある。このとき炉内に冷却ガスチューブを設置して冷却速度を制御してもよい。滞留時間ｔは材料が９８０〜９２０℃に存在する時間とする。
低温側焼鈍後は９２０℃未満〜７００℃の温度域から急冷する。この範囲を冷却開始温度とし、冷却速度を１０℃／秒以上とすることにより高磁束密度鋼板（高Ｂ8 ）が安定して得られる。
【００３３】
冷却速度を１０℃／ｓｅｃ以上とした理由は一定サイズ、一定量の変態相と固溶Ｃを確保するために必要であり、これもまた一次再結晶集合組織の適正化を図る上での役割を果たしているものと考えている。この結晶組織及び集合組織の適正化は冷間圧延後に行う脱炭焼鈍温度との組み合わせで達成される。
脱炭焼鈍は脱炭を行う他に前述したごとく一次再結晶組織の調整及び被膜形成に必要な酸化層を生成させる役割がある。
【００３４】
これは通常８００℃〜９００℃の温度域で湿水素，窒素ガスの混合ガス中で行う。脱炭焼鈍後は６５０℃〜８００℃の温度で水素, 窒素，アンモニアの混合ガス中で窒化処理を行う。６５０℃より低い温度では窒化効率が悪く、一方、８００℃以上でも効率が悪くなる上に一次再結晶粒径に影響してくるので好ましくない。
【００３５】
この後、ＭｇＯを主成分とする焼鈍分離剤を塗布して１１００℃以上の温度で仕上げ焼鈍をする。窒化処理としては上記の方法の他に、脱炭焼鈍後に塗布する燒鈍分離剤にに窒化能のある薬剤、例えばＭｎＮ，ＣｒＮ等を添加して塗布する方法を採用してもよい。
【００３６】
【実施例】
以下実施例について述べる。
Ｃ：０．０５６％，Ｓｉ：３．３５％，Ｍｎ：０．１０％，Ｓ：０．００７％，Ｎ：０．００８３％，Ｓｎ：０．０５％，Ｃｒ：０．１２％を含む溶鋼にＡｌの添加量を変えて酸可溶性Ａｌの変わった３種類の鋼塊を造った。
【００３７】

この鋼塊を１１５０℃で加熱、熱延し２．５ｍｍ厚の熱延板にした。この後熱延板焼鈍を次の条件で行った。
【００３８】
１１００℃×２分（在炉）＋８００℃×２分（在炉）→１００℃湯冷却
このとき、１１００℃から８００℃へ移行する過程で、冷却ガスを用いて冷却速度を変更し、９８０〜９２０℃の滞留時間を次の（イ）〜（ハ）の条件に調整した。
（イ）８０秒 （ロ）３４秒 （ハ）９秒
この後酸洗し０．２７ｍｍに冷延し，次いで８４０℃×１２０秒の脱炭焼鈍を露点６８℃の湿水素，窒素雰囲気ガス中で行った。引き続き窒化処理を７５０℃×３０秒間、乾水素，窒素アンモニアの混合ガス雰囲気中で行い、窒化後の鋼板の［Ｎ］量を２００ｐｐｍに調整した。この後ＭｇＯとＴｉＯ₂ を主成分とするスラリーを塗布乾燥した後１２００℃×２０時間の仕上げ焼鈍を行った。仕上げ焼鈍後の磁気特性は、表４に示すように、ＡｌR 値が低い試料（ａ）は（イ）の条件で、同じく（ｂ）は（イ）（ロ）の条件で高Ｂ8 が得られ、一方ＡｌR 値が高めの（ｃ）の材料は（ハ）の条件で高Ｂ8 が得られた。これはいずれも本発明の条件を満たすものである。
【００３９】
【表４】

【００４０】
【発明の効果】
本発明はＡｌ，Ｎの成分と、最終冷延前の鋼板焼鈍条件の関係を整理し、焼鈍条件を適正にして脱炭焼鈍し窒化処理を行うことにより、極めて高い磁束密度の一方向性電磁鋼板を安定して得ることができる。
【図面の簡単な説明】
【図１】磁束密度に及ぼすＡｌR と９８０〜９２０℃の滞留時間の影響関係を示す図である。
【図２】一次均熱温度と磁束密度の関係を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a unidirectional electrical steel sheet used as an iron core of an electric device, and particularly, a magnetic process in a manufacturing process in which a slab heating temperature is set to 1280 ° C. or less, that is, a manufacturing process in which an inhibitor is built after decarburization annealing. The present invention relates to a method for producing a unidirectional electrical steel sheet having excellent characteristics.
[0002]
[Prior art]
Unidirectional electrical steel sheets are mainly used as iron core materials for transformers, generators, and other electrical equipment, and have good coating properties as well as good excitation characteristics and iron loss characteristics. Must.
A unidirectional electrical steel sheet is obtained by developing a crystal grain having a so-called Goth orientation having a {110} plane on a rolling surface and a <001> axis in a rolling direction by utilizing a secondary recrystallization phenomenon.
[0003]
As is well known, the secondary recrystallization phenomenon occurs in the finish annealing temperature raising process, but in order to fully develop the secondary recrystallization, the secondary recrystallization phenomenon in the finish annealing temperature raising process is sufficient. Fine precipitates such as AlN, MnS, and MnSe that suppress the growth of primary recrystallized grains up to the crystal expression temperature range, so-called inhibitors, must be present in the steel. Therefore, the electromagnetic steel slab is heated to a high temperature such as 1350 to 1400 ° C. in order to completely dissolve a compound such as an inhibitor forming element such as Al, Mn, S, Se, and N. Thus, the inhibitor forming element completely dissolved in the electromagnetic steel slab is finely precipitated as AlN, MnS, and MnSe by annealing before the final cold rolling.
[0004]
In Japanese Patent Publication No. 46-23820, in the processing step of generating secondary recrystallized grains of {110} <001> orientation using a normal steel or silicon steel material which must contain C and Al, A method of precipitating AlN of a preferred size on a steel sheet by performing annealing immediately before cold rolling at 750 ° C. to 1200 ° C. and then rapidly cooling to 750 ° C. to 1200 ° C. or less according to the amount of Si is also disclosed in In No. 50-15727, in the production of a unidirectional electrical steel sheet in which silicon steel containing C, Al, Mn, N, Cu, etc. is hot-rolled and takes at least one cold rolling process, before the final cold rolling Annealing at 760 to 1177 ° C. for 15 seconds to 2 hours, from 927 ° C. or lower and from 400 ° C. or higher to at least 260 ° C., at a faster rate than natural cooling, from the highest temperature to 927 ° C. or lower. 400 to ℃ temperatures above has been proposed a method of cooling at a slower than the natural cooling rate.
[0005]
Any of these methods can be applied only to a raw material that is hot-rolled after the slab heating temperature is raised and the precipitate is completely dissolved. When such a process is adopted, the electromagnetic steel slab is heated to a high temperature as described above, so that a large amount of melt scale (noro) is generated, and the maintenance cost is increased by increasing the frequency of repairing the heating furnace. There are problems such as lowering the capacity factor and increasing the fuel consumption rate.
[0006]
In order to solve such a problem, a method for producing a unidirectional electrical steel sheet capable of lowering the heating temperature of the electrical steel slab has been developed. For example, Japanese Patent Publication No. 61-60896 discloses that the Mn content is 0.08 to 0.45%, the S content is 0.007% or less to lower the [Mn] [S] product, and Al, By using an electromagnetic steel slab containing P and N as a raw material, a manufacturing process capable of setting the slab heating temperature to less than 1280 ° C. is disclosed in Japanese Patent Application Laid-Open No. 3-211122, where Al, N, Sn, or B is further added. A similar process for heating and hot rolling the added electromagnetic steel slab at a temperature of 1200 ° C. or less has been proposed. These methods are characterized in that the inhibitor is not prepared in the previous process as in the high temperature slab heating material, but is built in the subsequent process after cold rolling, so that hot rolling and hot rolling sheet annealing are as much as in the high temperature slab material. No more strict management is needed.
[0007]
However, in industrial production, there are variations in components within a certain range, temperature and time variations in hot rolling, and in order to stabilize magnetic properties at a high level, it is possible to homogenize by hot-rolled sheet annealing. is necessary. As this annealing method, for example, in Japanese Patent Laid-Open No. 5-125446, annealing of a steel sheet before final cold rolling is performed as two-stage soaking, and the temperature on the high temperature side is determined from the components of the hot rolled sheet (acid-soluble Al-27 / 14 · N) is proposed.
[0008]
[Problems to be solved by the invention]
What is important in the manufacturing process in which the heating temperature of the electromagnetic steel slab is 1280 ° C. or lower is the adjustment of the crystal structure (average particle size, particle size distribution) and texture of the decarburized annealed plate and the preparation of inhibitors after the decarburized anneal (Nitriding).
In particular, it is known that the crystal structure and texture of the decarburized annealed plate have a great influence on the magnetic properties of the product. JP-A-2-259020 discloses the relationship between the average diameter of primary recrystallized grains and the magnetic flux density. It can be seen that it is important to adjust the crystal grains to a certain size.
[0009]
Factors affecting this structure include the cold rolling rate, the metal structure before cold rolling and the size and dispersion of precipitates, the annealing temperature after cold rolling, etc. Aside from (mainly the center ratio of Al and N), it is hot-rolled sheet annealing (including annealing before final cold rolling) and decarburization annealing. As one of the methods for solving this, Japanese Patent Laid-Open No. 5-125446 has been proposed. However, this method is not sufficient to widen the allowable range of component (AlR) variation generated in the steelmaking process.
[0010]
In addition, it is not preferable to adjust the primary recrystallization grain size by greatly changing the decarburization annealing temperature because it changes the quality and amount of the decarburization annealing oxide layer that affects the formation of the forsterite film. The present invention has been completed by examining in detail the relationship between the hot rolled sheet annealing cycle and the primary recrystallized grain growth behavior using the different materials of AlR.
[0011]
[Means for Solving the Problems]
The present invention will be described in detail below. The gist of the present invention is as follows.
(1) By weight, C: 0.025 to 0.075%, Si: 2.5 to 4.5%, Mn: 0.050 to 0.45%, S ≦ 0.015%, acid-soluble Al : 0.015 to 0.040%, Sn: 0.02 to 0.15%, Cr: 0.03 to 0.20%, and an electromagnetic steel slab composed of the remaining Fe and unavoidable impurities at 1280 ° C or less After heating to the temperature of, hot rolling, the final rolling rate is 80% or more by two or more rolling interposing annealing and one rolling or intermediate annealing, then decarburization annealing, from decarburization annealing In the manufacture of a unidirectional electrical steel sheet that is subjected to nitriding treatment and finish annealing before the secondary recrystallization start temperature, annealing of the steel sheet before the final cold rolling is performed in a two-stage cycle, and the high temperature side is temperature: The temperature is set to 1060 ° C. to 1170 ° C., and after soaking at this temperature within 180 seconds, the temperature on the low temperature side: 7 Relationship between AlR (acid-soluble Al-27 / 14 × N) (ppm) obtained from the components of hot-rolled sheet when the residence time of 980 ° C. to 920 ° C. in the process of moving to 0 to 980 ° C. is t seconds But,
3.14−0.0158 × AlR ≦ logt ≦ 3.85−0.0158 × AlR,
And t ≧ 10 sec
It cooled so as to satisfy the manufacturing method of an oriented electrical steel sheet you characterized by cooling at room temperature to 10 ° C. / sec or faster from the temperature range of 920 ° C. below to 700 ° C..
[0013]
(2) As a nitriding treatment to the steel sheet performed between the decarburization annealing and the secondary recrystallization start temperature, in a mixed gas of hydrogen, nitrogen and ammonia under the condition of running the strip at a temperature of 650 ° C. to 800 ° C. manufacturing method of an oriented electrical steel sheet according to be nitrided, characterized in (1).
[0014]
DETAILED DESCRIPTION OF THE INVENTION
First, hot-rolled sheet annealing, which is a feature of the present invention, will be described based on experimental results.
The material of the present invention has C: 0.055%, Si: 3.3%, Mn: 0.10%, S: 0.009% as base components, and acid-soluble Al and N are shown in Table 1. The ingot added in such a manner as described above was heated to 1150 ° C. and then hot-rolled to produce a hot-rolled sheet having a thickness of 2.3 mm.
[0015]
[Table 1]

Next, this hot-rolled sheet was annealed under the conditions shown in Table 2. The steel plate is annealed in a two-stage cycle, the high temperature side is soaked at 1120 ° C. for 30 seconds, the low temperature side temperature is set to 950 to 600 ° C., and the residence time is 980 ° C. to 920 ° C. during the transition from the high temperature side to the low temperature side. (Seconds) was measured.
[0016]
[Table 2]

Thereafter, pickling and cold rolling were performed to obtain a sheet thickness of 0.23 mm. Next, decarburization annealing was performed at 840 ° C. in an atmosphere of N ₂ : 25%, H ₂ : 75%, and dew point of 68 ° C. Next, nitriding treatment at 750 ° C. for 30 seconds was performed in a mixed gas of N ₂ , H ₂ and NH ₃ , and the nitrogen content of the steel sheet after nitriding was adjusted to 220 ppm. Thereafter, an annealing separator mainly composed of MgO and TiO ₂ was applied, and finish annealing was performed at 1200 ° C. for 20 hours.
[0017]
FIG. 1 shows the relationship of AlN—hot-rolled sheet annealing condition—magnetic flux density (B8). From this figure, the relationship between the residence time t (seconds) of 980 ° C. to 920 ° C. at which high magnetic flux density is obtained and AlR is as follows:
3.14−0.0158 × AlR ≦ logt ≦ 3.85−0.158 × AlR, t ≧ 10 sec
It turns out that it is.
[0018]
Next, the ingot No. 1 shown in Table 1 was used. 5 was used to examine the influence of the high temperature side temperature. Hot-rolled sheet annealing was performed under the conditions shown in Table 3. The residence time of 980 ° C. to 920 ° C. during the transition from the high temperature side to the low temperature side was adjusted so as to satisfy the above relationship.
[0019]
[Table 3]

The subsequent processing conditions were the same as described above. The result is shown in FIG.
[0020]
From FIG. 2, the temperature on the high temperature side obtained from B8: 1.93 T or more is in the range of 1060 ° C to 1170 ° C.
The reason why high B8 is obtained by such annealing has not been clarified yet, but at present, the following is considered. Factors affecting the secondary recrystallization phenomenon including the orientation of secondary recrystallization include primary recrystallization structure (average particle size, particle size distribution), texture, inhibitor strength, and the like. Changes in the texture and grain size distribution occur with the grain growth after the completion of primary recrystallization. In order to facilitate nucleation and grain growth of secondary recrystallization, it is desirable that the primary recrystallization structure has a uniform grain size and a certain size or more.
[0021]
On the other hand, the texture can obtain an appropriate amount of orientation grains ({110} <001> orientation, etc.) that undergo secondary recrystallization and orientation grains ({111} <112> orientation, etc.) that facilitate the growth of secondary recrystallization grains. is necessary. In addition to the rolling rate, this is affected by the crystal grain size (recrystallization rate) of the steel sheet before cold rolling, the amount of transformation phase, solute C, and the like.
In the process of the present invention, the presence of an inhibitor prior to cold rolling is not preferable because it makes adjustment of the primary recrystallization structure difficult, but precipitation of AlN is inevitable as long as Al and N are used as material components. In particular, control of fine precipitates is important. If the annealing conditions are the same, the smaller the AlR, the smaller the precipitation size, and the greater the primary recrystallized grain growth inhibiting power.
[0022]
Since Al, N, etc. of electromagnetic steel produced from a factory have a certain range of variation, when decarburized annealing is performed at the same temperature, a difference occurs in the primary recrystallized grain size, and the magnetic characteristics fluctuate. For this reason, it is necessary to adjust the decarburization annealing temperature and to stabilize the characteristics at a high level. However, when the decarburization annealing temperature is changed, the quality and quantity of the oxide layer are changed, which hinders the formation of a good forsterite film.
[0023]
The present invention stably manufactures a unidirectional electrical steel sheet having excellent magnetic properties by reducing the primary recrystallized grain size fluctuation caused by this component fluctuation and suppressing changes in the decarburization annealing temperature as much as possible. The reason why the change in the primary recrystallized grain size due to the variation in AlR is reduced by changing the residence time of 980 ° C to 920 ° C in the process of hot rolling annealing from the high temperature side to the low temperature side is as follows. ing.
[0024]
When hot-rolled sheet annealing is performed in a two-stage cycle, the precipitation nose region of AlN is in the range of 920 to 980 ° C., and it is considered that the precipitation depends on the length of residence time in this temperature region. Therefore, a material with a high AlR value, on which precipitates are likely to grow, lowers the retention temperature in the low temperature side, shortens the residence time in the precipitation nose region, and suppresses precipitation, while a material with a low AlR value has a longer precipitation time. It is thought that the inhibitor effect is controlled by promoting the above. When the passage time in the precipitation nose region is short, a part of the precipitation is finer during the decarburization annealing, so that the effect of suppressing primary recrystallized grain growth is large.
[0025]
Next, the reason for limiting the component composition of the electromagnetic steel slab as a starting material will be described.
When C content is less than 0.025%, secondary recrystallization becomes unstable, and even when secondary recrystallization occurs, the magnetic flux density (B8 value) of the product is as low as less than 1.80T. Become. On the other hand, if it exceeds 0.075%, the decarburization annealing time becomes long, and the productivity is remarkably impaired.
[0026]
When the content of Si is less than 2.5%, it is difficult to obtain a product with a low iron loss. On the other hand, when the content of Si exceeds 4.5%, the material is cracked during cold rolling. Breaks occur frequently, making stable cold rolling work impossible.
One of the characteristics in the component system of the starting material of the present invention is that S is 0.015% or less. Conventionally, in a known technique, for example, the technique disclosed in Japanese Patent Publication No. 40-15644 or Japanese Patent Publication No. 47-25250, S forms MnS which is a precipitate necessary for causing secondary recrystallization. It was essential as an element. In the known technology, there is a content range in which S exhibits the most effect, which is defined as an amount capable of dissolving MnS in the heating stage of the slab performed prior to hot rolling. However, MnS is not particularly necessary in the present invention using (Al, Si) N as an inhibitor. Rather, an increase in MnS is not preferable in terms of magnetic properties. Therefore, in the present invention, the S content is 0.015% or less.
[0027]
Al combines with N to form AlN. However, in the present invention, it is essential to form (Al, Si) N by nitriding steel after the completion of the subsequent step, that is, primary recrystallization. A certain amount or more of Al is required. Therefore, 0.015 to 0.040% is added as acid-soluble Al.
N needs to be 0.010% or less. Exceeding this causes blistering of the steel plate surface called blister. In addition, it becomes difficult to adjust the primary recrystallization structure. The lower limit is made 0.0020%. Below this value, it becomes difficult to develop secondary recrystallized grains.
[0028]
If the content of Mn is too small, secondary recrystallization becomes unstable, while if it is too much, it becomes difficult to obtain a product having a high magnetic flux density. The proper content is 0.050 to 0.45%.
Sn and Cr stabilize the formation of the film after finish annealing by adding together if necessary, and at the same time, Sn and Cr improve the texture after decarburization annealing, and thus the secondary recrystallized grains are reduced to a smaller size. Combined with stabilization, it is effective in improving iron loss. The appropriate amount of Sn is 0.02 to 0.15%, and if it is less than this, the effect is weak. No longer develops. Further, an appropriate amount of Cr is preferably 0.05 to 0.15%.
[0029]
An appropriate amount of Cu is 0.02 to 0.30%, and the magnetic flux density is improved in this range.
Note that the inclusion of a small amount of P and Ti in the steel does not impair the spirit of the present invention.
Next, the manufacturing process of the present invention will be described.
[0030]
The electromagnetic steel slab is obtained by melting steel in a melting furnace such as a converter or an electric furnace, vacuum degassing treatment as necessary, and then performing continuous casting or lump rolling after ingot forming.
Thereafter, slab heating is performed prior to hot rolling. In the process of the present invention, the slab heating temperature is as low as 1280 ° C. or less, and the consumption amount of heating energy is reduced, and the AlN in the steel is not completely dissolved but incompletely dissolved. Further, MnS having a higher solid solution temperature naturally becomes an incomplete solid solution state at the slab heating temperature. The slab is hot-rolled to produce a hot-rolled sheet having a predetermined thickness.
[0031]
The hot-rolled sheet is subsequently subjected to annealing and one cold rolling, or two or more rollings intervening intermediate annealing to obtain a final thickness. The finish cold rolling at this time is made 80% or more in order to obtain a high B8 value. As described above, as a condition of hot rolled sheet annealing or intermediate annealing prior to this final rolling, the relationship between the residence time t (seconds) from 980 ° C. to 920 ° C. during transition from the high temperature side to the low temperature side and AlR is as follows. ,
3.14−0.0158 × AlR ≦ logt ≦ 3.85−0.158 × AlR,
t ≧ 10sec
It is necessary to adjust to.
[0032]
As a result of various investigations on the annealing time, the soaking time on the high temperature side is preferably within 180 seconds. The temperature on the low temperature side needs to be 700 to 980 ° C. in order to ensure a residence time of 980 to 920 ° C. At this time, a cooling gas tube may be installed in the furnace to control the cooling rate. Residence time t is the time during which the material is present at 980-920 ° C.
After the low temperature side annealing, it is rapidly cooled from a temperature range of less than 920 ° C to 700 ° C. By setting this range as the cooling start temperature and setting the cooling rate to 10 ° C./second or more, a high magnetic flux density steel plate (high B8) can be obtained stably.
[0033]
The reason why the cooling rate is set to 10 ° C./sec or more is necessary to secure a certain size, a certain amount of transformation phase and solid solution C, and this also plays a role in optimizing the primary recrystallization texture. I believe that The optimization of the crystal structure and the texture is achieved in combination with a decarburization annealing temperature performed after cold rolling.
In addition to decarburization, the decarburization annealing has a role of generating an oxide layer necessary for adjusting the primary recrystallization structure and forming a film as described above.
[0034]
This is usually performed in a mixed gas of wet hydrogen and nitrogen gas at a temperature range of 800 ° C to 900 ° C. After decarburization annealing, nitriding is performed in a mixed gas of hydrogen, nitrogen and ammonia at a temperature of 650 ° C to 800 ° C. When the temperature is lower than 650 ° C., the nitriding efficiency is poor. On the other hand, when the temperature is 800 ° C. or higher, the efficiency is deteriorated and the primary recrystallized grain size is affected.
[0035]
Thereafter, an annealing separator containing MgO as a main component is applied and finish annealing is performed at a temperature of 1100 ° C. or higher. In addition to the above-described method, the nitriding treatment may be performed by adding a nitriding agent such as MnN or CrN to the annealing separator applied after decarburization annealing.
[0036]
【Example】
Examples will be described below.
C: 0.056%, Si: 3.35%, Mn: 0.10%, S: 0.007%, N: 0.0083%, Sn: 0.05%, Cr: 0.12% included Three types of steel ingots with different acid-soluble Al were made by changing the amount of Al added to the molten steel.
[0037]

This steel ingot was heated at 1150 ° C. and hot rolled to obtain a hot rolled sheet having a thickness of 2.5 mm. Thereafter, hot-rolled sheet annealing was performed under the following conditions.
[0038]
1100 ° C. × 2 minutes (in-furnace) + 800 ° C. × 2 minutes (in-furnace) → 100 ° C. Hot water cooling At this time, in the process of transition from 1100 ° C. to 800 ° C., the cooling rate is changed using 980-800 The residence time at 920 ° C. was adjusted to the following conditions (a) to (c).
(B) 80 seconds (b) 34 seconds (c) 9 seconds After this, pickling and cold rolling to 0.27 mm, followed by decarburization annealing at 840 ° C x 120 seconds in wet hydrogen and nitrogen atmosphere gas at a dew point of 68 ° C I went there. Subsequently, nitriding was performed at 750 ° C. for 30 seconds in a mixed gas atmosphere of dry hydrogen and nitrogen ammonia, and the [N] amount of the steel sheet after nitriding was adjusted to 200 ppm. Thereafter, a slurry mainly composed of MgO and TiO ₂ was applied and dried, and then finish annealing was performed at 1200 ° C. for 20 hours. As shown in Table 4, the magnetic properties after finish annealing are as follows. Samples (a) having a low AlR value are obtained under the conditions (a), and (b) is obtained under the conditions (a) and (b). On the other hand, the material (c) having a high AlR value obtained a high B8 under the condition (c). All of these satisfy the conditions of the present invention.
[0039]
[Table 4]

[0040]
【The invention's effect】
The present invention arranges the relationship between the components of Al and N and the steel sheet annealing conditions before the final cold rolling, performs decarburization annealing with appropriate annealing conditions, and performs nitriding treatment, thereby providing a unidirectional electromagnetic with extremely high magnetic flux density. A steel plate can be obtained stably.
[Brief description of the drawings]
FIG. 1 is a diagram showing an influence relationship between AlR and a residence time of 980 to 920 ° C. on magnetic flux density.
FIG. 2 is a diagram showing a relationship between primary soaking temperature and magnetic flux density.

Claims (2)

By weight, C: 0.025 to 0.075%, Si: 2.5 to 4.5%, Mn: 0.050 to 0.45%, S ≦ 0.015%, acid-soluble Al: 0. An electromagnetic steel slab containing 015 to 0.040%, Sn: 0.02 to 0.15%, Cr: 0.03 to 0.20%, and the balance Fe and unavoidable impurities at a temperature of 1280 ° C or lower After heating, it is hot-rolled, and the final rolling rate is set to 80% or more by two or more rolling steps including annealing and one-time rolling or intermediate annealing, and then decarburization annealing is performed. In the manufacture of a unidirectional electrical steel sheet that is subjected to nitriding treatment and finish annealing before the crystallization start temperature, annealing of the steel sheet before final cold rolling is performed in a two-stage cycle, and the high temperature side is temperature: 1060 ° C. to 1170 ° C. After soaking at this temperature within 180 seconds, the temperature on the low temperature side: 700 to If the 980 ℃ ~920 residence time of ° C. in the course of transition to 80 ° C. was t seconds, the relationship between AlR obtained from components of the hot rolled sheet (acid-soluble Al-27/14 × N) (ppm) is,
3.14−0.0158 × AlR ≦ logt ≦ 3.85−0.0158 × AlR,
And t ≧ 10 sec
It cooled so as to satisfy the manufacturing method of an oriented electrical steel sheet you characterized by cooling at room temperature to 10 ° C. / sec or faster from the temperature range of 920 ° C. below to 700 ° C.. As nitriding treatment to the steel sheet performed from the decarburization annealing to the secondary recrystallization start temperature, nitriding in a mixed gas of hydrogen, nitrogen and ammonia under the condition that the strip runs at a temperature of 650 ° C to 800 ° C. manufacturing method of an oriented electrical steel sheet according to claim 1, wherein the.

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