JP4240921B2 - Non-oriented electrical steel sheet with low iron loss after magnetic annealing - Google Patents

Description

【００１７】
表１より、Ｖ：０．００４％材ではＶ：ｔｒ．に比べ鉄損が著しく高いことがわかる。この原因を調査するため、ＴＥＭにてＳＲＡ後のサンプルの組織観察を行った。ＴＥＭの観察結果、Ｖ：０．００４％材においては８０ｎｍ程度の非常に微細なＶＮが粒界に多数認められ、このＶＮが粒成長性を阻害しているものと判明した。
【００１８】
以上のＴＥＭ観察結果から、鉄損を低減するためには、Ｖを低減することが単純かつ効果的な手法と考えられる。Ｖを安定して低減するためには、Ｖ混入量の少ない低Ｖ鉱を使用するか、製鋼段階でＶを低減する必要がある。しかし、低Ｖ鉱のみを使用することは鉄鉱石の弾力運用ができないばかりでなく大幅なコストアップに繋がる。また、製鋼段階でＶを低減するためには、スラグボリュームを増やすことによりＶを溶鋼からスラグ中に移動させる必要があり、スラグ量の増大に繋がることとなる。
【００１９】
そこで、Ｖ混入を前提とした粒成長性向上手法について検討を行った。Ｃ：０．００２５％、Ｓｉ：０．５％、Ｍｎ：０．５０％、Ｐ：０．１００％、Ａｌ：ｔｒ、Ｓ：０．００３％、Ｎ：０．００２０％、Ｖ：０．００４％とした鋼を溶解し、熱延後、酸洗した。引き続き、熱延板焼鈍をまず８００℃×３ｈｒの条件で、次いで、７２０℃×０．１〜６ｈｒと変化させて行うことにより析出物形態を変化させ、次いで、板厚０．５ｍｍまで冷間圧延を行った。次いで、７２０℃×１ｍｉｎ間の仕上焼鈍を施し、さらに、７５０℃×２ｈｒの磁性焼鈍を施した。
【００２０】
このようにして得られたサンプルの析出物形態を調査するため、板厚中央部から薄膜を採取し、析出物のサイズに応じ倍率１０００〜１００００倍にてＴＥＭ観察を行った。観察視野は０．０５ｍｍ² とした。その結果、上記成分系において観察される析出物はＶＮ、ＭｎＳであり、熱延板焼鈍条件の違いにより、析出物のサイズ、凝集状態が異なっていることが観察された。そこでＭｎＳ、ＶＮが複合析出し粗大化している個数と、ＭｎＳ、ＶＮがそれぞれ個別に存在している個数で整理を行った。
【００２１】
図１は、このようにして得られたサンプルの鉄損W１５／５０と析出物との関係を示したものである。
【００２２】
図１より、ＭｎＳとＶＮの複合析出物の個数が、ＭｎＳ、ＶＮの個別に存在している個数を含む全析出物数の２０％以上となった場合に鉄損が低下していることがわかる。
【００２３】
この複合析出により粒成長性が向上するメカニズムは以下のように考えられる。
【００２４】
熱延の巻取時に微細に単独析出したＶＮは、仕上焼鈍時に再固溶するが、ＳＲＡ時に再度ＶＮとして結晶粒界に優先析出し、粒界を強固にピンニングすることにより粒成長性を低下させる。これに対し、熱延板焼鈍条件の適正化により、ＭｎＳを核として複合析出したＶＮは、熱力学的に安定なため短時間仕上焼鈍時にはほとんど固溶しない。このため、ＳＲＡ時に単独析出する微細なＶＮ量が少なくなり粒成長性が向上したものと考えられる。
【００２５】
以上のことから、ＳＲＡ時の粒成長性を向上させるためにはＶＮをＭｎＳに複合析出させることが効果的であり、図１より複合析出物個数が全析出物数の２０％以上となった場合に鉄損が低下することから、本発明では、（ＭｎＳとＶＮの複合析出物数）／（ＭｎＳ+ＶＮ＋ＭｎＳとＶＮの複合析出物数）≧０．２とする。
【００２６】
次に、その他の成分の限定理由について説明する。
【００２７】
Ｓｉは鋼板の固有抵抗を上げるために有効な元素であるが、１．５％を超えると飽和磁束密度の低下に伴い磁束密度が低下するため上限を１．５％以下とした。
【００２８】
Ａｌは、微量に添加した場合には微細なＡｌＮを形成し、磁気特性を阻害するため、０．００４％以下とした。
【００２９】
Ｃは磁気時効の問題があるため０．００５％以下とした。
【００３０】
Ｍｎは熱間圧延時の赤熱脆性を防止するために、０．１％以上必要であるが、１％を超えると磁束密度を低下させるので０．１〜１％とした。
【００３１】
Ｓは一般にはＭｎＳを形成し粒成長性を阻害するため、極力低減することが求められている。しかし、本発明ではＶＮの析出核として重要な役割を果たす元素であり、下限を０．００１％とする。Ｓが０．０２％超えとなった場合にはＭｎＳの析出量が多くなり、粒成長性が低下するため上限を０．０２％とする。
【００３２】
Ｖは０．０１％超となると、窒化物以外のたとえば炭化物等を形成し粒成長性を阻害するため０．０１％以下が好ましい。また、Ｖを０．００１％以下とすることは著しいコストアップとなるため下限を０．００１％とする。
【００３３】
Ｐは鋼板の打ち抜き性を改善するために必要な元素であるが、０．２％を超えて添加すると鋼板が脆化するため０．２％以下とした。
【００３４】
なお、Ｓｂ、Ｓｎ、Ｂ、Ｚｒを磁気特性向上のために添加することは何ら差しつかえない。
【００３５】
次に、本発明の無方向性電磁鋼板の製造方法について説明する。
【００３６】
本発明においては、鋼板中のＭｎＳとＶＮの析出形態が所定の範囲内となっていればよく、例えば、７５０〜８５０℃程度で３〜１０時間程度の長時間熱延板焼鈍を行うことによりＭｎＳのオストワルド成長を図り、引き続きＶＮの析出域となる７００〜７５０℃程度で３〜１０時間程度の熱延板焼鈍を行うことによりＭｎＳ−ＶＮ複合析出物を形成させることができる。上記は一例であって、本発明の無方向性電磁鋼板の製造方法はこの方法に限定されるものではない。鋼板中のＭｎＳとＶＮの析出形態をはじめ、他の成分についても本発明範囲を満たしていればよく、製造方法については通常の方法でかまわない。すなわち転炉で吹練した溶鋼を脱ガス処理し所定の成分に調整し、引き続き鋳造、熱間圧延を行う。熱間圧延後、熱延板焼鈍を施し、次いで一回の冷間圧延、もしくは中間焼鈍をはさんだ２回以上の冷間圧延により所定の板厚とした後に、最終焼鈍を行う。
【００３７】
【実施例】
表２に示す鋼を用い、転炉で吹練した後に脱ガス処理を行うことにより所定の成分に調整後鋳造し、板厚２．０ｍｍまで熱間圧延を行った。次にこの熱延板を酸洗し、ＭｎＳとＶＮの析出物形態を制御するため表２に示す種々の条件で熱延板焼鈍を行った。その後、板厚０．５ｍｍまで冷間圧延を行い、表２に示す仕上焼鈍条件で焼鈍を行い、さらに７５０℃×２ｈｒの磁性焼鈍を行った。
【００３８】
これら鋼板サンプルについて、磁気特性を評価した。磁気特性は２５ｃｍエプスタイン試験片を用いて行った。各鋼板の磁気特性を表２に併せて示す。
【００３９】
【表２】

【００４０】
表２より、ＭｎＳとＶＮの析出物形態を本発明の範囲に制御した本発明鋼では、磁性焼鈍後の鉄損の非常に低い鋼板が得られることがわかる。
【００４１】
一方、成分もしくはＭｎＳとＶＮの析出物形態が本発明範囲外である比較例では、磁性焼鈍後の鉄損の値が非常に高いか、鉄損の値は低いが磁束密度の低下という別の問題を生じていることがわかる。
【００４２】
【発明の効果】
以上述べたように、本発明によれば、Ａｌフリ−系の電磁鋼板において、磁性焼鈍後の鉄損の低い鋼板を得ることができる。また、本発明はＶ混入を前提としているため、高価な低Ｖ鉱を使用したり製綱段階での長時間製錬を行ったりする必要はなく、経済的である。
【図面の簡単な説明】
【図１】ＭｎＳ−ＶＮ複合析出物比率と鉄損との関係を示す図。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a non-oriented electrical steel sheet with low iron loss after magnetic annealing.
[0002]
[Prior art]
Non-oriented electrical steel sheets are classified into full-process materials and semi-process materials depending on the manufacturing method. Of these, full-process materials obtain predetermined magnetic properties by finish annealing on the steel manufacturer's side, while semi-process materials obtain predetermined magnetic properties by performing strain relief annealing after punching at the customer. To get.
[0003]
In the semi-process material, at the time of strain relief annealing, crystal grains grow at the same time as the removal of the processing strain, so that the iron loss can be further reduced. For this reason, strain relief annealing is also called “magnetic annealing”.
[0004]
In order to improve the grain growth during magnetic annealing, it is effective to reduce the amount of inclusions and precipitates in the steel sheet. In particular, since V mixed as an impurity precipitates as VN during SRA and inhibits grain growth, various methods for detoxifying VN have been proposed.
[0005]
For example, Japanese Patent Laid-Open No. 10-18006 discloses a technique for fixing N as AlN by adding 0.1 to 1.0% of Al and detoxifying VN.
[0006]
However, recently, from the viewpoint of motor recycling, there are cases where the motor core is melted and used as a casting in a motor frame or the like. When electromagnetic steel sheets to which Al is added are recycled for casting as scrap, Since the viscosity of the resin increases and shrinkage cavities occur, it is difficult to recycle, and it is necessary to make Al substantially free.
[0007]
As a technique for reducing iron loss in Al-free steel, Japanese Patent No. 2718410 discloses Si: 1.0% or less, Al: 0.004% or less, and the relationship between V and N in the steel is log (V × N) < An electromagnetic steel sheet is disclosed in which the iron loss is reduced by setting −5.44.
[0008]
[Problems to be solved by the invention]
However, in order to stably reduce V, it is necessary to use expensive low-V ore or to perform refining for a long time in the steelmaking stage, and it is inevitable that the cost increases. .
[0009]
The present invention has been made in view of such circumstances, and an object thereof is to provide a non-oriented electrical steel sheet having low iron loss after magnetic annealing in an Al-free electrical steel sheet.
[0010]
[Means for Solving the Problems]
As a result of intensive studies on non-oriented electrical steel sheets with low iron loss after magnetic annealing in Al-free electrical steel sheets, the present inventors have obtained the following knowledge. That is, when the present inventors examined the improvement of grain growth during magnetic annealing of the V-mixed material, by aggregating VN with MnS as a nucleus, grain growth is remarkably improved, and low iron loss can be achieved. .
[0011]
This invention is made | formed based on the said knowledge, and has the following structures.
[0012]
In mass%, C: 0.005% or less, Si: 1.5% or less, Al: 0.004% or less, P: 0.2% or less, Mn: 0.1 to 1%, S: 0.001 -0.02%, V: 0.001-0.01%, N: 0.005% or less, comprising the balance Fe and inevitable impurities , VN and MnS satisfy the following relationship Non- oriented electrical steel sheet.
[0013]
Number of composite precipitates of MnS and VN / (Number of composite precipitates of MnS + VN + MnS and VN) ≧ 0.2
In addition, in this specification, all% which shows the component of steel is mass%.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
First, the present invention will be described in detail based on experimental results.
[0015]
In order to investigate the effects of V and N on iron loss, C: 0.0030%, Si: 0.30%, Mn: 0.30%, P: 0.100%, Al: tr, S: 0.00. 002%, N: 0.0025%, V: tr. And V: 0.004% of two steel types were dissolved in a laboratory, and after hot rolling, pickling was performed. Subsequently, this hot-rolled sheet was cold-rolled to a thickness of 0.5 mm, subjected to finish annealing for 720 ° C. × 1 min, and further subjected to magnetic annealing at 750 ° C. × 2 hr. Table 1 shows the iron loss values of the samples thus obtained. Here, the measurement of magnetic characteristics was performed using a 25 cm Epstein test piece.
[0016]
[Table 1]

[0017]
From Table 1, V: tr. It can be seen that the iron loss is significantly higher than In order to investigate this cause, the structure of the sample after SRA was observed by TEM. As a result of TEM observation, in the V: 0.004% material, a very large number of very fine VNs of about 80 nm were observed at the grain boundaries, and it was found that these VNs hindered grain growth.
[0018]
From the above TEM observation results, it is considered that reducing V is a simple and effective technique for reducing iron loss. In order to stably reduce V, it is necessary to use low V ore with a small amount of V mixing or to reduce V in the steelmaking stage. However, using only low V ore not only does not allow the elastic operation of iron ore, but also leads to a significant cost increase. In addition, in order to reduce V in the steelmaking stage, it is necessary to move V from molten steel into the slag by increasing the slag volume, leading to an increase in the amount of slag.
[0019]
Therefore, a method for improving grain growth on the premise of V mixing was examined. C: 0.0025%, Si: 0.5%, Mn: 0.50%, P: 0.100%, Al: tr, S: 0.003%, N: 0.0020%, V: 0.00. 004% steel was melted, hot rolled, and pickled. Subsequently, the hot-rolled sheet annealing was first performed under conditions of 800 ° C. × 3 hr, and then changed to 720 ° C. × 0.1-6 hr to change the precipitate form, and then cold-rolled to a thickness of 0.5 mm. Rolled. Next, finish annealing was performed for 720 ° C. × 1 min, and magnetic annealing was further performed at 750 ° C. × 2 hr.
[0020]
In order to investigate the precipitate form of the sample thus obtained, a thin film was collected from the central part of the plate thickness, and TEM observation was performed at a magnification of 1000 to 10,000 times according to the size of the precipitate. The observation visual field was 0.05 mm ² . As a result, it was observed that the precipitates observed in the above component system were VN and MnS, and the size and agglomeration state of the precipitates were different due to the difference in the hot-rolled sheet annealing conditions. Therefore, the number of MnS and VN compositely precipitated and coarsened, and the number of MnS and VN existing individually were arranged.
[0021]
FIG. 1 shows the relationship between the iron loss W15 / 50 of the sample thus obtained and the precipitate.
[0022]
From FIG. 1, it can be seen that iron loss is reduced when the number of composite precipitates of MnS and VN is 20% or more of the total number of precipitates including the number of MnS and VN existing individually. Recognize.
[0023]
The mechanism by which the grain growth property is improved by this composite precipitation is considered as follows.
[0024]
VN, which is finely precipitated during hot rolling, re-dissolves during finish annealing, but preferentially precipitates again at the grain boundaries as VN during SRA, reducing the grain growth by pinning the grain boundaries firmly. Let On the other hand, VN that has been complex-precipitated with MnS as the nucleus by optimizing the hot-rolled sheet annealing conditions is thermodynamically stable and hardly dissolves during short-time finish annealing. For this reason, it is considered that the amount of fine VN that precipitates alone during SRA is reduced and the grain growth property is improved.
[0025]
From the above, in order to improve the grain growth at the time of SRA, it is effective to complex precipitate VN into MnS. From FIG. 1, the number of complex precipitates is 20% or more of the total number of precipitates. In this case, since the iron loss is reduced, in the present invention, (number of composite precipitates of MnS and VN) / (number of composite precipitates of MnS + VN + MnS and VN) ≧ 0.2.
[0026]
Next, the reasons for limiting other components will be described.
[0027]
Si is an effective element for increasing the specific resistance of the steel sheet. However, if it exceeds 1.5%, the magnetic flux density decreases with a decrease in saturation magnetic flux density, so the upper limit was made 1.5% or less.
[0028]
When Al is added in a small amount, fine AlN is formed and the magnetic properties are hindered, so the content is made 0.004% or less.
[0029]
C has a problem of magnetic aging, so it is made 0.005% or less.
[0030]
Mn is required to be 0.1% or more in order to prevent red hot brittleness during hot rolling, but if it exceeds 1%, the magnetic flux density is lowered, so it was made 0.1 to 1%.
[0031]
In general, S is required to be reduced as much as possible because it forms MnS and inhibits grain growth. However, in the present invention, it is an element that plays an important role as a precipitation nucleus of VN, and the lower limit is made 0.001%. When S exceeds 0.02%, the precipitation amount of MnS increases and the grain growth property decreases, so the upper limit is made 0.02%.
[0032]
When V exceeds 0.01%, for example, carbide other than nitride is formed and the grain growth is inhibited, so 0.01% or less is preferable. Further, if V is made 0.001% or less, the cost will increase significantly, so the lower limit is made 0.001%.
[0033]
P is an element necessary for improving the punchability of the steel sheet, but if added over 0.2%, the steel sheet becomes brittle, so it was made 0.2% or less.
[0034]
It should be noted that Sb, Sn, B, and Zr can be added to improve the magnetic characteristics.
[0035]
Next, the manufacturing method of the non-oriented electrical steel sheet of this invention is demonstrated.
[0036]
In the present invention, the precipitation form of MnS and VN in the steel sheet only needs to be within a predetermined range. For example, by performing long-time hot-rolled sheet annealing at about 750 to 850 ° C. for about 3 to 10 hours. MnS-VN composite precipitates can be formed by performing Ostwald growth of MnS and subsequently performing hot-rolled sheet annealing for about 3 to 10 hours at about 700 to 750 ° C., which is a VN precipitation region. The above is an example, and the method for producing the non-oriented electrical steel sheet of the present invention is not limited to this method. It is sufficient that other components including the precipitation form of MnS and VN in the steel sheet satisfy the scope of the present invention, and the production method may be a normal method. That is, the molten steel blown in the converter is degassed and adjusted to a predetermined component, followed by casting and hot rolling. After hot rolling, hot-rolled sheet annealing is performed, and then the final annealing is performed after the cold rolling is performed once or a predetermined sheet thickness is obtained by two or more cold rolling sandwiching the intermediate annealing.
[0037]
【Example】
The steel shown in Table 2 was blown in a converter and then degassed and then cast into a predetermined component, which was then cast and hot rolled to a thickness of 2.0 mm. Next, this hot-rolled sheet was pickled and subjected to hot-rolled sheet annealing under various conditions shown in Table 2 in order to control the form of precipitates of MnS and VN. Then, it cold-rolled to plate | board thickness 0.5mm, annealed on the finishing annealing conditions shown in Table 2, and also magnetic annealing of 750 degreeC x 2 hr was performed.
[0038]
These steel plate samples were evaluated for magnetic properties. Magnetic properties were obtained using 25 cm Epstein specimens. The magnetic properties of each steel sheet are also shown in Table 2.
[0039]
[Table 2]

[0040]
From Table 2, it can be seen that in the steel of the present invention in which the precipitate form of MnS and VN is controlled within the range of the present invention, a steel sheet having a very low iron loss after magnetic annealing can be obtained.
[0041]
On the other hand, in the comparative example in which the precipitates of the components or MnS and VN are outside the scope of the present invention, the iron loss value after magnetic annealing is very high, or the iron loss value is low but the magnetic flux density is reduced. You can see that there is a problem.
[0042]
【The invention's effect】
As described above, according to the present invention, a steel sheet having low iron loss after magnetic annealing can be obtained in an Al-free electromagnetic steel sheet. In addition, since the present invention is premised on the inclusion of V, it is not necessary to use expensive low-V ore or to perform smelting for a long time at the steelmaking stage, which is economical.
[Brief description of the drawings]
FIG. 1 is a view showing a relationship between a MnS-VN composite precipitate ratio and iron loss.

Claims (1)

In mass%, C: 0.005% or less, Si: 1.5% or less, Al: 0.004% or less, P: 0.2% or less, Mn: 0.1 to 1%, S: 0.001 -0.02%, V: 0.001-0.01%, N: 0.005% or less, comprising the balance Fe and inevitable impurities , VN and MnS satisfy the following relationship Non- oriented electrical steel sheet.
Number of composite precipitates of MnS and VN / (Number of composite precipitates of MnS + VN + MnS and VN) ≧ 0.2

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