JP3889100B2 - Method for producing non-oriented electrical steel sheet with excellent magnetic properties - Google Patents

Description

【００１７】
同表に示したとおり、いずれの条件下においても、ＡのCaSi添加の方が鉄損特性に優れている。
【００１８】
実験２
Ｃ：0.003 wt％，Si：3.2 wt％，Mn：0.3 wt％，Ｐ：0.01wt％，Al：0.6 wt％を含有し、残部は実質的にFeの組成になる鋼を、転炉および真空脱ガスにより成分調整した。この時の鋼中Ｏ量は 0.007wt％であった。その後、
Ａ：CaSi合金添加、
Ｂ：CaＯ，CaF₂の混合物を主成分とする通常の脱硫フラックス添加、
Ｃ：CaSi合金と通常の脱硫フラックスの併用
により、それぞれＳ：0.0040wt％まで脱硫した。引き続き連続鋳造により厚み：215 mm、幅：1100mmのスラブとした。
ついで、通常のガス加熱炉により、表２に示す種々の温度に加熱した後、熱間圧延により厚み：2.8 mmの熱延板とした。その後、1000℃, 60秒の熱延板焼鈍後、１回の冷間圧延で厚み：0.5 mmの冷延板とした後、 850℃, 30秒の再結晶焼鈍を施して製品板とした。
かくして得られた製品板の磁気特性について調べた結果を表２に併記する。
【００１９】
【表２】

【００２０】
同表によれば、いずれのスラブ加熱条件下においても、CaSi添加したＡが最も特性が良く、ついでCaSiと通常の脱硫フラックスを併せて添加したＣ、通常の脱硫フラックスのみ添加したＢの順に鉄損特性が悪くなっている。
また、スラブ加熱温度が高い場合の方が鉄損特性の差が大きくなっている。
【００２１】
実験２で用いたスラブから採取したサンプルについて析出物分析を行った。
その結果、Ａ，Ｂ，Ｃいずれの場合も析出物はAl（Ｏ，Ｎ）と複合形態をとっているものが頻繁に観察されたが、析出物中に含まれるAlの割合はＡで多く、Ｂでは少ない傾向にあった。
また、サルファイドについては、Ａはほとんどがカルシウム−サルファイドまたはカルシウム−オキシサルファイドで、析出物中にMnは含まれていなかったのに対し、Ｂでは（Mn, Fe）Ｓのような複合した析出物が主で、Caはほとんど含まれなかった。またＣは、（Ca, Mn, Fe）Ｓであり、ＡとＢの中間的な析出物を形成していた。なお、この析出物中のMn比率は13％であった。
【００２２】
このことから、CaSi脱硫により形成されたカルシウム−（オキシ）サルファイドは、MnＳの形成を抑制するだけでなく、溶鋼中のAl₂O₃ 等の介在物を有効に凝集、粗大化させ、さらに低温ではAlＮの優先析出サイトとして作用したものと考えられる。そして、このような析出物の粗大化、すなわち数密度の低減により粒成長性が改善されたものと考えられる。
【００２３】
実験３
Ｃ：0.005 wt％，Si：2.85wt％，Mn：0.2 wt％，Ｐ：0.01wt％，Al：0.3 wt％を含有し、残部は実質的にFeの組成になる鋼を、転炉および真空脱ガスにより成分調整した。この時の鋼中Ｏ量を表３に示す。
ついで、CaSi合金添加により、それぞれＳ：0.0060wt％まで脱硫した。引き続き連続鋳造により厚み：215 mm、幅：1100mmのスラブとした。
これらのスラブを、通常のガス加熱炉で1100℃に加熱した後、熱間圧延により厚み：2.2 mmの熱延板とした。
その後、1000℃, 60秒の熱延板焼鈍後、１回の冷間圧延により厚み：0.5 mmの冷延板とした後、 820℃, 30秒の再結晶焼鈍を施して製品板とした。
かくして得られた製品板の磁気特性およびCa系硫化物中におけるMnの重量比率について調べた結果を、表３に併記する。
【００２４】
【表３】

【００２５】
同表に示された結果から、真空脱ガス処理後の鋼中Ｏ量が0.01％以下で、Ca系硫化物中におけるMnの重量比率が10％以下の場合に、良好な磁気特性が得られている。
【００２６】
以上の結果より、鋼中に分散する硫化物系介在物が、単独もしくはAl酸化物、Al窒化物と複合したCa硫化物あるいはCa酸硫化物であり、それらの硫化物系介在物に含まれるMnが重量比率で10％以下である場合に低鉄損の無方向性電磁鋼板が得られることが判る。
また、無方向性電磁鋼板を製造するに際しては、転炉、真空脱ガス処理にて成分調整し、鋼中酸素量をＯ≦0.01wt％とした溶鋼に、連続鋳造までの過程でCaSi合金を添加してＳ≦0.01wt％まで脱硫することにより、上記のような低鉄損の無方向性電磁鋼板の製造が可能であることが判る。
【００２７】
実験４
Ｃ：0.003 wt％，Si：1.0 wt％，Mn：0.2 wt％，Ｐ：0.02wt％，Al：0.3 wt％を含有し、残部は実質的にFeの組成になる鋼を、転炉および真空脱ガスにより成分調整した。この時の鋼中Ｏ量は表４に示すとおりであった。その後、
Ａ：CaSi合金添加、
Ｂ：CaＯ，CaF₂の混合物を主成分とする通常の脱硫フラックス添加
により、それぞれＳ：0.0080wt％まで脱硫した。引き続き連続鋳造により厚み：215 mm、幅：1100mmのスラブとした。
ついで、通常のガス加熱炉により1150℃に加熱した後、熱間圧延により厚み：2.8 mmの熱延板とした。その後、1000℃, 60秒の熱延板焼鈍後、１回の冷間圧延で厚み：0.5 mmの冷延板とした後、 850℃, 60秒の再結晶焼鈍を施して製品板とした。
かくして得られた製品板の磁気特性について調べた結果を表４に併記する。
【００２８】
【表４】

【００２９】
同表の結果によれば、同程度のＳ量レベルで比較すると、CaSi合金添加したＡの特性の方が良く、通常の脱硫フラックス添加したＢの方が鉄損特性が悪くなっている。
【００３０】
実験２の製品版から採取したサンプルについて析出物調査を行った。
その結果、いずれの場合も析出物はAl（Ｏ，Ｎ）と複合形態をとっているものが頻繁に観察された。サルファイドについては、Ａはほとんどがカルシウム−サルファイドまたはカルシウム−オキシサルファイドであった。これに対してＢでは（Mn, Fe）Ｓのような複合した析出物が主で、Caはほとんど含まれていなかった。
また、ＳＥＭ写真の画像解析処理によって析出物の粒径を調査した結果を、同じく表４に示したが、それによれば、CaSi合金を添加して脱硫する場合には真空脱ガス処理後の鋼中Ｏ量が少ないほど粗大な析出物が多く、特に磁気特性の良好な製品では 0.5μm 以上の析出物の個数比率が50％以上であることが判る。
この点、通常の脱硫フラックスを添加した場合には、真空脱ガス処理後の鋼中Ｏ量の如何にかかわらず、比較的微細な析出物の比率が高いことが判明した。
この析出物形態の違いのため磁気特性に差が生じたものと考えられる。
【００３１】
実験５
Ｃ：0.005 wt％，Si：0.25wt％，Mn：0.25wt％，Ｐ：0.07wt％，Al：0.25wt％を含有し、残部は実質的にFeの組成になる鋼を、転炉および真空脱ガスにより成分調整した。この時の鋼中Ｏ量は 0.015wt％以下であった。
ついで、CaSi合金添加により、それぞれＳ：0.015 wt％以下まで脱硫した。引き続き連続鋳造により厚み：215 mm、幅：1100mmのスラブとした。
これらのスラブを、通常のガス加熱炉で1100℃に加熱した後、熱間圧延により厚み：2.4 mmの熱延板とした。
その後、熱延板焼鈍を施すことなく、１回の冷間圧延により厚み：0.5 mmの冷延板とした後、 820℃, 30秒の再結晶焼鈍を施して製品板とした。
これらの製品板での析出物調査結果と、得られた製品板にさらに 750℃, ２時間の歪取焼鈍を施した後の磁気特性についての調査結果を、図１に併せて示す。
【００３２】
同図から明らかなように、真空脱ガス処理後の鋼中Ｏ量が0.01wt％以下で、かつCaSi合金の添加によりＳ≦0.01wt％まで脱硫した場合に、とりわけ良好な鉄損特性が得られる判る。
なお、一部の実験材については、Ｓが0.01wt％以上またはＯが0.01wt％以上であっても良好な特性のものが得られたが、良好な特性の得られた製品では粗大な析出物が多く 0.5μm 以上の析出物の個数比率が50％以上である点で共通していた。
【００３３】
以上の結果より、鋼中に分散する硫化物系介在物が、単独もしくはAl酸化物、Al窒化物と複合したCa硫化物あるいはCa酸硫化物であり、しかもかかる硫化物系介在物のうち直径が 0.5μm 以上のものの個数比率が50％以上である場合に、低鉄損の無方向性電磁鋼板が得られることが判る。
また、無方向性電磁鋼板を製造するに際しては、転炉、真空脱ガス処理にて成分調整し、鋼中酸素量をＯ≦0.01wt％とした溶鋼に、連続鋳造までの過程でCaSi合金を添加してＳ≦0.01wt％まで脱硫することにより、上記のような低鉄損の無方向性電磁鋼板の製造が可能であることが判る。
【００３４】
実験６
Ｃ：0.003 wt％，Si：0.18wt％，Mn：0.30wt％，Ｐ：0.07wt％，Al：0.35wt％を含有し、残部は実質的にFeの組成になる鋼を、転炉および真空脱ガスにより成分調整した。この時の鋼中Ｏ量は 0.008wt％であった。その後、
Ａ：CaSi合金添加、
Ｃ：CaSi合金と通常の脱硫フラックスの複合添加
により、それぞれＳ：0.004 wt％まで脱硫した。引き続き連続鋳造により厚み：225 mm、幅：1120mmのスラブとした。
ついで、通常のガス加熱炉により1100℃に加熱した後、熱間圧延により厚み：2.6 mmの熱延板とした。その後、1000℃, 30秒の熱延板焼鈍後、表５に示すように No.45, 46については１回冷延法で、また No.47, 48については２回冷延法でそれぞれ、厚み：0.35mmの冷延板としたのち、同じく表５に示す条件下で仕上げ焼鈍を施して製品板とした。
かくして得られた製品板の磁気特性について調べた結果を表５に併記する。
【００３５】
【表５】

【００３６】
同表から明らかなように、CaSi脱硫を行い１回冷延法により製造した場合に最も優れた磁気特性が得られ、特に歪取り焼鈍後の特性が良好であった。
【００３７】
このような析出物制御によって良好な磁気特性が得られる理由については必ずしも明確に解明されたわけではないが、実験１、実験２の結果よりCaSi添加材の方が鉄損特性が良好であり、特にスラブ加熱温度および熱延板焼鈍温度が高い場合の鉄損特性の劣化を防止するのに有効であることから、以下のように考えられる。
すなわち、無方向性電磁鋼板にとって最も重要な特性である鉄損は、製品の結晶粒径に大きく依存し、その粒径は析出物の分散状態に影響される。通常の脱硫フラックス添加したＢで形成された固溶温度の低い（Mn, Fe）Ｓは、スラブ加熱、熱延板焼鈍、再結晶焼鈍で固溶・再析出により微細分散するため粒成長を阻害するのに対して、CaSi脱硫をしたＡで形成されたCaＳは、鋼中で安定で溶解度が極めて低いため、固溶、再析出せず、従って微細化しないため、粒成長性が良好だったものと考えられる。一方Ｃでは、複合析出物の中でも（Mn, Fe）Ｓの部分が固溶・再析出したため、Ａに比べて鉄損特性が劣化したものと考えられる。
また、CaSi合金を用いて脱硫しても、鋼中Ｏ量が高い場合および残存Ｓ量が多い場合には、微細な析出物の比率が高くなり、粒成長抑制力が強くなるばかりでなく、硫化物系介在物中のＯ比率が高まり、Ｓ量に対して相対的にCaが不足するため、Mn硫化物が増加し、その結果磁気特性が改善されなかったものと考えられる。
【００３８】
さらに、２回冷延法では中間焼鈍の分だけ焼鈍回数が多くなるため、複合介在物中のAlＮ等の固溶温度の低い成分の分離が進行していると考えられる。介在物の複合化による粒成長性向上効果は、このような低固溶温度成分の分解・再析出により相殺されてしまう。従って、複合析出物中のAl含有率の高いCaSi脱硫材の方がこの影響を受け易いため、２回冷延法では、CaSi合金と通常の脱硫フラックスを併用したＣの場合よりも特性が悪くなったものと考えられる。
この点、１回冷延法では、少なくとも中間焼鈍がないため、AlＮ等の分解は少なく、従って１回冷延法では、CaSi合金と通常の脱硫フラックスを併用したＣよりも優れた磁気特性が得られたものと考えられる。
従って、CaSiによる介在物制御は１回冷延法に適したものであると言える。
【００３９】
次に、この発明において成分組成を前記の範囲に限定した理由について説明する。
Ｃ：0.01wt％以下
Ｃは、γ域を拡大し、α−γ変態点を低下させる。焼鈍中にγ相がα粒界にフィルム状に生成しα粒の成長を抑制するため、Ｃは基本的に少なくする必要がある。また、SiやAl等のα相安定化元素を多量に含有し、全温度域でγ相が生成しない場合でも鉄損特性の時効劣化を引き起こすので、Ｃ含有量は0.01wt％以下とする必要がある。なお、下限は特に限定されないが、コスト等の面から0.0005wt％以上とすることが望ましい。
【００４０】
Si：3.5 wt％以下
Siは、鋼の比抵抗を高め鉄損を低下させる有用元素であり、目標とする磁気特性に応じて含有量を変化させる。しかしながら、同時に硬度も上昇させ、冷間圧延性を悪化させるので、上限を 3.5wt％とした。なお、下限は特に定めるものではないが、比抵抗を高める観点から0.05wt％以上含有させることが望ましい。
【００４１】
Al：2.5 wt％以下
Alは、Siと同様に、鋼の比抵抗を高め鉄損を低下させる元素であり、目標とする磁気特性に応じて含有量を変化させる。しかしながら、その含有量が多い場合には連続鋳造時にモールドとの潤滑性が低下し、鋳造が困難となるので、上限を2.5 wt％に定めた。
【００４２】
Mn：1.5 wt％
Mnも、SiやAlほどではないが鋼の比抵抗を高め、鉄損を低下させる効果があり、また熱間圧延性を改善する効果もある。しかしながら、多量に含有すると冷間圧延性が劣化するので、上限を 1.5wt％に定めた。
【００４３】
Ｓ：0.01wt％以下
Ｓは、析出物、介在物を形成し粒成長性を阻害するので、極力低減すべき元素である。この発明は、CaSiを脱硫に用い、Ｓの析出形態を制御するによってＳを無害化するものであるが、鋼中における残存量が多い場合には、介在物の粒子数が増え、またＳを固定するためのCaが相対的に不足すると介在物中のMnＳの割合が増え、やはり粒成長性に悪影響を及ぼすので、Ｓは0.01wt％以下まで低減するものとした。
【００４４】
Ｐ：0.1 wt％以下
Ｐも、SiやAlほどではないが鋼の比抵抗を高め、鉄損を低下させる効果があるだけでなく、粒界偏析により冷延再結晶後の集合組織を改善して磁束密度を向上させる効果がある。しかしながら、過度に添加すると粒界偏析量が多くなってかえって粒成長性を阻害し鉄損を劣化させるので、0.1 wt％以下で含有させるものとした。
【００４５】
以上、必須成分について説明したが、その他にも各種の公知元素を添加することが可能であり、例えば磁気特性改善成分としてＢ，Ni, Cu, Sb, Sn, BiおよびGe等を添加することができる。
【００４６】
次に、製造方法について説明する。
この発明では、前述したとおり、鋼の溶製段階において、鋼中Ｏ量を0.01wt％以下とした上で、CaSi合金の添加により、鋼中Ｓ濃度を0.01wt％以下まで脱硫することが重要である。
というのは、鋼中Ｏ量および鋼中Ｓ量が0.01wt％を超えると、Ca硫化物系中のMnの比率が10％超となったり、硫化物系介在物のうち直径：0.5 μm 以上のものの個数比率が50％未満となって、満足いくほどの改善効果が得られないからである。
なお、鋼中Ｏ量やＳ量が0.01wt％を超えていても、直径：0.5 μm 以上の介在物の個数比率が50％以上であれば、良好な磁気特性を得ることができる。
【００４７】
溶製後のスラブ製造条件や、熱間圧延条件、冷間圧延条件および仕上げ焼鈍条件については、特に限定されることはなく、常法に従って行えば良い。
【００４８】
【実施例】
供試鋼としては、表６に示す成分組成になる鋼種を用いた。各鋼種は、転炉および真空脱ガスにより成分調整し、鋼中Ｏ量を0.007 wt％以下とした上で、表７に示す方法でＳ≦0.01wt％まで脱硫して得たものである。
上記の各溶鋼を、連続鋳造により、厚み：225 mm、幅：1100〜1250mmのスラブとした。ついで、表７に示す条件下で、スラブ加熱を行った後、熱間圧延し、その後、熱延板焼鈍を施したのち、または施さずに、１回の冷間圧延で厚み：0.5 mmの冷延板としたのち、再結晶焼鈍を施して製品板とした。
かくして得られた製品板の磁気特性について調べた結果を表７に併記する。
【００４９】
【表６】

【００５０】
【表７】

【００５１】
表７から明らかなように、この発明に従いCaSi脱硫したものは、通常の脱硫フラックスを用いて脱硫した比較例に比べて、磁気特性とくに鉄損特性が改善されている。
【００５２】
【発明の効果】
かくして、この発明に従い、脱硫剤としてCaSi合金を有効に活用することによって、従来に比べより効果的に硫化物系介在物の形態制御を行うことができ、ひいては粒成長性を向上ならしめ、もって鉄損特性の一層の向上を実現することができる。
【図面の簡単な説明】
【図１】真空脱ガス処理後の鋼中Ｏ量、脱硫処理後の鋼中Ｓ量および粗大析出物の個数比率が鉄損特性に及ぼす影響を示したグラフである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a non-oriented electrical steel sheet having excellent magnetic properties, and in particular, intends to advantageously improve iron loss characteristics by controlling the precipitation form of sulfide inclusions in the steel plate. is there.
[0002]
[Prior art]
It is known that the iron loss characteristics of non-oriented electrical steel sheets largely depend on the crystal grain size of the product plate, and basically it is necessary to coarsen the crystal grain size in order to obtain a product with low iron loss. ing. The grain growth property is greatly influenced by the second phase dispersed in the steel, that is, precipitates and inclusions, and greatly depends on its components, size distribution, and dispersion state. Since these precipitates have the effect of pinning the movement of grain boundaries, it goes without saying that such precipitates need to be reduced as much as possible in order to improve grain growth.
[0003]
However, at the present industrial technical level, it is extremely difficult to melt highly clean steel in which precipitates and inclusions in steel are reduced to such an extent that they do not affect grain growth, and in the production of general-purpose practical materials. Since the cost problem cannot be ignored, it is practically impossible to melt such a clean steel.
[0004]
For this reason, a certain amount of precipitates and inclusions are unavoidably left in the steel, resulting in the deterioration of magnetic properties.
In particular, when precipitates with a relatively low solid solution temperature such as MnS and AlN are formed, they are once dissolved in the process of slab heating, hot-rolled sheet annealing, recrystallization annealing after cold rolling, and the like. The fine precipitates were reprecipitated in stages, and the fine precipitates had a very large grain growth suppressing effect, and thus the magnetic properties were significantly deteriorated.
[0005]
As means for avoiding this solid solution / reprecipitation, there are methods of lowering the slab heating temperature, the hot-rolled sheet annealing temperature, and the recrystallization annealing temperature after cold rolling.
However, although lowering the slab heating temperature has the effect of preventing solid solution of precipitates, the hot rolling temperature also decreases accordingly, which not only makes rolling difficult, but also does not recrystallize the hot rolled sheet. Since the grain size is small even if a part remains or is recrystallized, the texture of the product plate is deteriorated by subsequent cold rolling and recrystallization, which is not preferable for the product characteristics of the non-oriented electrical steel sheet.
Similarly, in the method of lowering the hot-rolled sheet annealing temperature, recrystallization and grain growth become insufficient, and deterioration of the texture of the product plate is inevitable.
Further, when the recrystallization annealing temperature is lowered, the grain growth rate is rather slow due to the low temperature, and a sufficient grain size cannot be obtained with a limited annealing time.
As described above, there is a limit to obtain a product having good magnetic properties without causing the precipitates to be dissolved or re-precipitated, and a particular effect cannot be expected.
[0006]
In addition, there is a method for controlling the form of precipitates as a means of avoiding the bad effects of precipitates, etc. As such a form control method for precipitates, solid solution such as REM sulfide or Sb sulfide is used as the form control method for such precipitates. A method of fixing as a high temperature precipitate (Japanese Patent Laid-Open No. 51-62115), a method of adding Zr in the same manner as REM (Japanese Patent Publication No. 1-52448, Japanese Patent Laid-Open No. 51-60624), etc. However, in order to obtain a sufficient effect by these methods, it is necessary to add a large amount of an expensive auxiliary material, which raises the cost of the product. In addition, REM sulfide has a very complicated precipitation form like (REM, Mn, Al, Si) (O, S), and is difficult to float in the melt and remains in large quantities in the steel. There is also. Therefore, even though the solid solution temperature of REM sulfide (mainly Ce sulfide) alone is high, it is actually a composite precipitate, so it was partially dissolved and re-precipitated to deteriorate the grain growth property.
[0007]
Similarly, as a method for fixing S in steel, there is a method using Ca (Japanese Patent Publication No. 58-17248, Japanese Patent Publication No. 59-74213, Japanese Patent Publication No. 58-17249, etc.).
However, when a desulfurization flux (usually including CaO, CaF ₂ ) such as JP-B-58-17248 and JP-A-59-74213 is used, the sulfide inclusion component is Al (O, N) + (Ca, Mn) (S, O) becomes very complicated, and MnS that forms inclusions in the heating process such as slab heating and hot-rolled sheet annealing before hot rolling is a solid solution -Grain growth is also hindered because it is refined by reprecipitation.
[0008]
For this reason, it is difficult to say that the sulfide has been sufficiently rendered harmless, and has left a problem particularly when a further reduction in iron loss is intended by the single cold rolling method.
This is because, in the case of the cold rolling two-time method, since the cold rolling reduction before finish annealing is low, the driving force of recrystallization is weak and the number of recrystallized nuclei generated is small, resulting in relatively coarse grains. It is easy to reduce iron loss, but in the case of the single cold rolling method, since the cold rolling reduction ratio is high, the recrystallization driving force is high, and the number of nucleation is large, so it tends to become fine grains. This is because improvement of grain growth is more important for reducing the iron loss than the double cold rolling method.
[0009]
In addition, as seen in Japanese Examined Patent Publication No. 58-17249, when metallic Ca is used, it is not only difficult to store and handle because Ca is a very active metal, but also vapor at the molten steel temperature. Since the pressure is high, it is difficult to obtain an effective desulfurization effect by vaporization immediately after the addition, and a large amount of addition is required. Further, there is a problem that the smoke during the addition is intense and the working working environment is remarkably deteriorated.
[0010]
[Problems to be solved by the invention]
As described above, in order to obtain good magnetic properties in a non-oriented electrical steel sheet, it is necessary to ensure sufficient grain growth, and it is particularly important to control the precipitates that affect it. However, no effective and inexpensive control method has been developed on an industrial level.
The present invention advantageously solves the above problems, and in the case of using the single cold rolling method, which is superior in terms of process and cost, by controlling sulfide inclusions more effectively than in the past. , tighten not improve the grain growth property, and thereby to propose a more advantageous method for producing a non-oriented electrical steel sheet that achieved improvement of iron loss characteristics.
[0011]
[Means for Solving the Problems]
Now, the inventors have found, after intensive studies to achieve the above object, it is possible to reduce the steel S by CaSi, it relates achieve the intended purpose, to obtain a knowledge that it is very effective .
The present invention is based on the above findings.
[0014]
That is , this invention
C: 0.01 wt% or less,
Si: 3.5 wt% or less,
Mn: 1.5 wt% or less,
Al: 2.5 wt% or less,
S: 0.01 wt% or less,
P: In producing a non-oriented electrical steel sheet containing 0.1 wt% or less, with the balance being substantially Fe, by a single cold rolling method,
Components are adjusted by converter and vacuum degassing treatment, and CaSi alloy is added to the molten steel whose oxygen content in the steel is 0.01wt% or less until the completion of casting. S concentration in steel: 0.01wt% or less by desulfurizing up, the weight ratio of Mn contained in the sulfide inclusions to be formed is 10% or less, and the diameter of the sulfides inclusions: the number ratio of 0.5 mu m or more of 50% is a manufacturing how excellent non-oriented electrical steel sheets of the magnetic properties, characterized in that the least.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the background to the completion of the present invention will be described based on experimental results.
Experiment 1
C: 0.003 wt%, Si: 2.0 wt%, Mn: 0.3 wt%, P: 0.03 wt%, Al: 0.2 wt%, with the balance being substantially Fe composition, converter and vacuum Components were adjusted by degassing. At this time, the amount of O in the steel was 0.004 wt%. afterwards,
A: Addition of CaSi alloy,
B: CaO, by conventional desulfurization flux additive based on a mixture of CaF _2, each S: desulfurized to 0.007 wt%. Subsequently, a slab having a thickness of 215 mm and a width of 1100 mm was obtained by continuous casting.
These slabs were heated to 1150 ° C. with a normal gas heating furnace, and then hot rolled into hot rolled sheets having a thickness of 2.6 mm. Thereafter, hot-rolled sheet annealing was performed or omitted to obtain a cold-rolled sheet having a thickness of 0.5 mm by one cold rolling, and then recrystallized annealing to obtain a product sheet. The hot-rolled sheet annealing and recrystallization annealing at this time were performed under the conditions shown in Table 1.
The results of examining the magnetic properties of the product plate thus obtained are also shown in Table 1.
[0016]
[Table 1]

[0017]
As shown in the table, under any condition, the addition of CaSi of A is superior in iron loss characteristics.
[0018]
Experiment 2
C: 0.003 wt%, Si: 3.2 wt%, Mn: 0.3 wt%, P: 0.01 wt%, Al: 0.6 wt%, with the balance being substantially Fe composition, converter and vacuum Components were adjusted by degassing. At this time, the amount of O in the steel was 0.007 wt%. afterwards,
A: Addition of CaSi alloy,
B: Addition of normal desulfurization flux mainly composed of a mixture of CaO and CaF ₂
C: Each was desulfurized to S: 0.0040 wt% by the combined use of a CaSi alloy and a normal desulfurization flux. Subsequently, a slab having a thickness of 215 mm and a width of 1100 mm was obtained by continuous casting.
Subsequently, after heating to various temperatures shown in Table 2 with a normal gas heating furnace, hot rolled sheets having a thickness of 2.8 mm were formed by hot rolling. Then, after hot-rolled sheet annealing at 1000 ° C. for 60 seconds, a cold rolled sheet having a thickness of 0.5 mm was formed by one cold rolling, and then recrystallized annealing at 850 ° C. for 30 seconds to obtain a product sheet.
The results of examining the magnetic properties of the product plate thus obtained are also shown in Table 2.
[0019]
[Table 2]

[0020]
According to the table, under any slab heating condition, A with added CaSi has the best characteristics, followed by C in which CaSi and normal desulfurized flux are added together, and B in which only normal desulfurized flux is added. Loss characteristics are getting worse.
Moreover, the difference in iron loss characteristics is larger when the slab heating temperature is higher.
[0021]
Precipitate analysis was performed on the sample collected from the slab used in Experiment 2.
As a result, in all cases of A, B, and C, precipitates were frequently observed in a composite form with Al (O, N), but the ratio of Al contained in the precipitates was large with A. , B tended to be less.
As for sulfide, A is mostly calcium-sulfide or calcium-oxysulfide, and Mn is not contained in the precipitate, whereas B is a composite precipitate such as (Mn, Fe) S. However, Ca was hardly contained. C was (Ca, Mn, Fe) S, and an intermediate precipitate between A and B was formed. The Mn ratio in this precipitate was 13%.
[0022]
From this, calcium- (oxy) sulfide formed by CaSi desulfurization not only suppresses the formation of MnS, but also effectively aggregates and coarsens inclusions such as Al ₂ O ₃ in the molten steel, and further lowers the temperature. Therefore, it is thought that it acted as a preferential precipitation site of AlN. And it is thought that the grain growth property was improved by such coarsening of the precipitates, that is, reduction of the number density.
[0023]
Experiment 3
C: 0.005 wt%, Si: 2.85 wt%, Mn: 0.2 wt%, P: 0.01 wt%, Al: 0.3 wt% of steel, the balance being substantially Fe composition, converter and vacuum Components were adjusted by degassing. The amount of O in steel at this time is shown in Table 3.
Subsequently, each was desulfurized to S: 0.0060 wt% by addition of CaSi alloy. Subsequently, a slab having a thickness of 215 mm and a width of 1100 mm was obtained by continuous casting.
These slabs were heated to 1100 ° C. in a normal gas heating furnace, and then hot rolled into hot rolled sheets having a thickness of 2.2 mm.
Then, after hot-rolled sheet annealing at 1000 ° C. for 60 seconds, a cold rolled sheet having a thickness of 0.5 mm was formed by one cold rolling, and then recrystallized annealing at 820 ° C. for 30 seconds to obtain a product sheet.
Table 3 shows the magnetic properties of the product plate thus obtained and the results of examining the weight ratio of Mn in the Ca-based sulfide.
[0024]
[Table 3]

[0025]
From the results shown in the table, good magnetic properties are obtained when the amount of O in steel after vacuum degassing is 0.01% or less and the weight ratio of Mn in Ca-based sulfide is 10% or less. ing.
[0026]
From the above results, the sulfide inclusions dispersed in the steel are Ca sulfide or Ca oxysulfide alone or in combination with Al oxide, Al nitride, and are included in those sulfide inclusions It can be seen that a non-oriented electrical steel sheet with low iron loss can be obtained when Mn is 10% or less by weight.
Also, when manufacturing non-oriented electrical steel sheets, the components are adjusted by converters and vacuum degassing treatment, and then the CaSi alloy is added to the molten steel with the oxygen content in the steel set to O ≤ 0.01 wt%. It can be seen that the non-oriented electrical steel sheet having the low iron loss as described above can be produced by adding and desulfurizing to S ≦ 0.01 wt%.
[0027]
Experiment 4
C: 0.003 wt%, Si: 1.0 wt%, Mn: 0.2 wt%, P: 0.02 wt%, Al: 0.3 wt% of steel, the balance being substantially Fe composition, converter and vacuum Components were adjusted by degassing. The amount of O in steel at this time was as shown in Table 4. afterwards,
A: Addition of CaSi alloy,
B: CaO, by conventional desulfurization flux additive based on a mixture of CaF _2, each S: desulfurized to 0.0080wt%. Subsequently, a slab having a thickness of 215 mm and a width of 1100 mm was obtained by continuous casting.
Subsequently, after heating to 1150 ° C. by a normal gas heating furnace, a hot rolled sheet having a thickness of 2.8 mm was formed by hot rolling. Then, after hot-rolled sheet annealing at 1000 ° C. for 60 seconds, a cold rolled sheet having a thickness of 0.5 mm was formed by one cold rolling, and then recrystallized annealing at 850 ° C. for 60 seconds to obtain a product sheet.
The results of examining the magnetic properties of the product plate thus obtained are also shown in Table 4.
[0028]
[Table 4]

[0029]
According to the results in the table, when compared at the same S level, the characteristics of A added with a CaSi alloy are better, and the characteristics of B added with a normal desulfurized flux are worse.
[0030]
Precipitates were investigated for samples collected from the product version of Experiment 2.
As a result, in all cases, the precipitate was frequently observed in a composite form with Al (O, N). For sulfide, A was mostly calcium-sulfide or calcium-oxysulfide. On the other hand, in B, composite precipitates such as (Mn, Fe) S were mainly contained, and Ca was hardly contained.
The results of investigating the particle size of the precipitates by image analysis processing of SEM photographs are also shown in Table 4. According to this, when desulfurization is performed by adding a CaSi alloy, the steel after vacuum degassing treatment is used. It can be seen that the smaller the amount of medium O, the larger the coarse precipitates, and the number ratio of precipitates of 0.5 μm or more is 50% or more, especially in products with good magnetic properties.
In this regard, it has been found that when a normal desulfurization flux is added, the ratio of relatively fine precipitates is high regardless of the amount of O in the steel after the vacuum degassing treatment.
It is considered that the difference in magnetic properties was caused by the difference in the form of precipitates.
[0031]
Experiment 5
Steel containing C: 0.005 wt%, Si: 0.25 wt%, Mn: 0.25 wt%, P: 0.07 wt%, Al: 0.25 wt%, the balance being substantially Fe composition, converter and vacuum Components were adjusted by degassing. At this time, the amount of O in the steel was 0.015 wt% or less.
Subsequently, each was desulfurized to S: 0.015 wt% or less by adding a CaSi alloy. Subsequently, a slab having a thickness of 215 mm and a width of 1100 mm was obtained by continuous casting.
These slabs were heated to 1100 ° C. in a normal gas heating furnace and then hot rolled to form hot rolled sheets having a thickness of 2.4 mm.
Then, without performing hot-rolled sheet annealing, a cold-rolled sheet having a thickness of 0.5 mm was formed by one cold rolling, and then recrystallized annealing at 820 ° C. for 30 seconds to obtain a product sheet.
Fig. 1 shows the results of the investigation of the precipitates on these product plates, and the results of the investigation on the magnetic properties after the obtained product plates were further subjected to strain relief annealing at 750 ° C for 2 hours.
[0032]
As is clear from the figure, particularly good iron loss characteristics are obtained when the amount of O in steel after vacuum degassing is 0.01 wt% or less and desulfurization is performed up to S ≦ 0.01 wt% by the addition of CaSi alloy. I understand.
For some experimental materials, good characteristics were obtained even when S was 0.01 wt% or more or O was 0.01 wt% or more, but coarse precipitation was observed in products with good characteristics. It was common in that the number ratio of many precipitates of 0.5 μm or more was 50% or more.
[0033]
From the above results, the sulfide inclusions dispersed in the steel are Ca sulfide or Ca oxysulfide alone or in combination with Al oxide, Al nitride, and the diameter of such sulfide inclusions. It can be seen that a non-oriented electrical steel sheet having a low iron loss can be obtained when the number ratio of those having a thickness of 0.5 μm or more is 50% or more.
Also, when manufacturing non-oriented electrical steel sheets, the components are adjusted by converters and vacuum degassing treatment, and then the CaSi alloy is added to the molten steel with the oxygen content in the steel set to O ≤ 0.01 wt%. It can be seen that the non-oriented electrical steel sheet having the low iron loss as described above can be produced by adding and desulfurizing to S ≦ 0.01 wt%.
[0034]
Experiment 6
C: 0.003 wt%, Si: 0.18 wt%, Mn: 0.30 wt%, P: 0.07 wt%, Al: 0.35 wt%, with the balance being substantially Fe composition, converter and vacuum Components were adjusted by degassing. At this time, the amount of O in the steel was 0.008 wt%. afterwards,
A: Addition of CaSi alloy,
C: Each was desulfurized to 0.004 wt% by the combined addition of CaSi alloy and ordinary desulfurization flux. Subsequently, a slab having a thickness of 225 mm and a width of 1120 mm was obtained by continuous casting.
Next, after heating to 1100 ° C. with a normal gas heating furnace, hot rolled sheets were formed by hot rolling to a thickness of 2.6 mm. Then, after hot-rolled sheet annealing at 1000 ° C. for 30 seconds, as shown in Table 5, No. 45 and 46 were cold-rolled once, and No. 47 and 48 were cold-rolled twice. After forming a cold-rolled sheet having a thickness of 0.35 mm, a final annealing was performed under the conditions shown in Table 5 to obtain a product sheet.
The results of examining the magnetic properties of the product plate thus obtained are also shown in Table 5.
[0035]
[Table 5]

[0036]
As is apparent from the table, the most excellent magnetic properties were obtained when CaSi desulfurization was performed and the product was produced by a single cold rolling method, and particularly the properties after strain relief annealing were good.
[0037]
Although the reason why good magnetic properties can be obtained by such precipitate control is not necessarily clearly clarified, the CaSi additive has better iron loss properties than the results of Experiments 1 and 2, and in particular, Since it is effective in preventing deterioration of iron loss characteristics when the slab heating temperature and hot-rolled sheet annealing temperature are high, it is considered as follows.
That is, the iron loss, which is the most important characteristic for the non-oriented electrical steel sheet, greatly depends on the crystal grain size of the product, and the grain size is affected by the dispersion state of the precipitates. Low (Mn, Fe) S formed by B with normal desulfurized flux added is finely dispersed by solid solution / reprecipitation through slab heating, hot-rolled sheet annealing, and recrystallization annealing, thus inhibiting grain growth. On the other hand, CaS formed from A with CaSi desulfurization was stable in steel and very low in solubility, so it did not solid solution, re-precipitate, and therefore did not become finer, so grain growth was good. It is considered a thing. On the other hand, in C, the (Mn, Fe) S portion of the composite precipitate was dissolved and reprecipitated, so that it is considered that the iron loss characteristics were deteriorated compared to A.
In addition, even when desulfurizing using a CaSi alloy, when the amount of O in the steel is high and the amount of residual S is large, the ratio of fine precipitates is increased, and not only the grain growth suppression power is increased, It is considered that the O ratio in the sulfide inclusions is increased and Ca is relatively insufficient with respect to the amount of S, so that Mn sulfide is increased, and as a result, the magnetic properties are not improved.
[0038]
Furthermore, in the double cold rolling method, the number of annealing is increased by the amount of the intermediate annealing, so that it is considered that the separation of components having a low solid solution temperature such as AlN in the composite inclusion is proceeding. The effect of improving the grain growth property due to the composite of inclusions is offset by the decomposition / reprecipitation of such a low solid solution temperature component. Therefore, since the CaSi desulfurization material having a high Al content in the composite precipitate is more susceptible to this influence, the double cold rolling method has worse properties than the case of C using both the CaSi alloy and the normal desulfurization flux. It is thought that it became.
In this regard, since there is no intermediate annealing in the one-time cold rolling method, there is little decomposition of AlN and the like. Therefore, in the one-time cold rolling method, magnetic properties superior to C using a combination of CaSi alloy and ordinary desulfurization flux are obtained. It is thought that it was obtained.
Therefore, it can be said that inclusion control by CaSi is suitable for the single cold rolling method.
[0039]
Next, the reason why the component composition is limited to the above range in the present invention will be described.
C: 0.01 wt% or less C expands the γ region and lowers the α-γ transformation point. In order to suppress the growth of α grains by forming a γ phase in the form of a film at the α grain boundary during annealing, it is basically necessary to reduce C. Also, it contains a large amount of α-phase stabilizing elements such as Si and Al, and even if no γ-phase is generated at all temperatures, it causes aging deterioration of iron loss characteristics. Therefore, the C content must be 0.01 wt% or less. There is. The lower limit is not particularly limited, but is preferably 0.0005 wt% or more from the viewpoint of cost and the like.
[0040]
Si: 3.5 wt% or less
Si is a useful element that increases the specific resistance of steel and lowers iron loss, and changes the content according to the target magnetic properties. However, at the same time, the hardness is increased and the cold rolling property is deteriorated, so the upper limit was made 3.5 wt%. The lower limit is not particularly defined, but is preferably 0.05% by weight or more from the viewpoint of increasing the specific resistance.
[0041]
Al: 2.5 wt% or less
Al, like Si, is an element that increases the specific resistance of steel and decreases iron loss, and changes its content according to the target magnetic properties. However, when the content is large, the lubricity with the mold is lowered during continuous casting, and casting becomes difficult, so the upper limit was set to 2.5 wt%.
[0042]
Mn: 1.5 wt%
Although Mn is not as high as Si and Al, it has the effect of increasing the specific resistance of steel and reducing the iron loss, and also has the effect of improving hot rollability. However, the cold rolling property deteriorates when contained in a large amount, so the upper limit was set to 1.5 wt%.
[0043]
S: 0.01 wt% or less S is an element to be reduced as much as possible because it forms precipitates and inclusions and inhibits grain growth. In this invention, CaSi is used for desulfurization, and S is rendered harmless by controlling the precipitation form of S. However, when the residual amount in steel is large, the number of inclusion particles increases, and S If Ca for fixing is relatively insufficient, the ratio of MnS in the inclusions increases, which also adversely affects the grain growth. Therefore, S is reduced to 0.01 wt% or less.
[0044]
P: 0.1 wt% or less P is not only as effective as Si and Al, but it has the effect of increasing the specific resistance of steel and lowering iron loss. It also improves the texture after cold rolling recrystallization by grain boundary segregation. This has the effect of improving the magnetic flux density. However, if excessively added, the amount of segregation at the grain boundary increases, which rather hinders the grain growth and deteriorates the iron loss.
[0045]
The essential components have been described above, but various other known elements can be added. For example, B, Ni, Cu, Sb, Sn, Bi and Ge can be added as components for improving magnetic characteristics. it can.
[0046]
Next, a manufacturing method will be described.
In the present invention, as described above, it is important to desulfurize the S concentration in the steel to 0.01 wt% or less by adding a CaSi alloy after the O content in the steel is 0.01 wt% or less in the steel melting stage. It is.
This is because when the amount of O in steel and the amount of S in steel exceeds 0.01 wt%, the ratio of Mn in Ca sulfide system exceeds 10%, and the diameter of sulfide inclusions is 0.5 μm or more. This is because the number ratio is less than 50%, and a satisfactory improvement effect cannot be obtained.
Even if the amount of O or S in steel exceeds 0.01 wt%, good magnetic properties can be obtained if the number ratio of inclusions having a diameter of 0.5 μm or more is 50% or more.
[0047]
The slab manufacturing conditions after melting, the hot rolling conditions, the cold rolling conditions, and the finish annealing conditions are not particularly limited, and may be performed according to ordinary methods.
[0048]
【Example】
As the test steel, steel types having the composition shown in Table 6 were used. Each steel type was obtained by adjusting the components by a converter and vacuum degassing so that the amount of O in the steel was 0.007 wt% or less and desulfurizing to S ≦ 0.01 wt% by the method shown in Table 7.
Each molten steel was formed into a slab having a thickness of 225 mm and a width of 1100 to 1250 mm by continuous casting. Subsequently, after slab heating was performed under the conditions shown in Table 7, hot rolling was performed, and then, after or without hot-rolled sheet annealing, the thickness was 0.5 mm by one cold rolling. After forming a cold-rolled sheet, recrystallization annealing was performed to obtain a product sheet.
The results of examining the magnetic properties of the product plate thus obtained are also shown in Table 7.
[0049]
[Table 6]

[0050]
[Table 7]

[0051]
As is apparent from Table 7, the magnetic properties, particularly the iron loss properties, of the CaSi desulfurized product according to the present invention are improved as compared with the comparative example obtained by desulfurization using a normal desulfurized flux.
[0052]
【The invention's effect】
Thus, according to the present invention, by effectively using a CaSi alloy as a desulfurizing agent, it is possible to control the form of sulfide inclusions more effectively than in the past, thereby improving grain growth. Further improvement in iron loss characteristics can be realized.
[Brief description of the drawings]
FIG. 1 is a graph showing the influence of the amount of O in steel after vacuum degassing, the amount of S in steel after desulfurization, and the number ratio of coarse precipitates on iron loss characteristics.

Claims (1)

C: 0.01 wt% or less,
Si: 3.5 wt% or less,
Mn: 1.5 wt% or less,
Al: 2.5 wt% or less,
S: 0.01 wt% or less,
P: In producing a non-oriented electrical steel sheet containing 0.1 wt% or less, with the balance being substantially Fe, by a single cold rolling method,
Components are adjusted by converter and vacuum degassing treatment, and CaSi alloy is added to the molten steel whose oxygen content in the steel is 0.01wt% or less until the completion of casting. S concentration in steel: 0.01wt% or less by desulfurizing up, the weight ratio of Mn contained in the sulfide inclusions to be formed is 10% or less, and the diameter of the sulfides inclusions: the number ratio of 0.5 mu m or more of 50% The manufacturing method of the non-oriented electrical steel sheet excellent in the magnetic characteristics characterized by the above-mentioned .

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