JP2005040835A - Mold powder for continuous casting of steel - Google Patents
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本発明は、鋼を連続鋳造する際に使用するモールドパウダーに関するものである。 The present invention relates to a mold powder used when continuously casting steel.
近年、鋼の清浄化に対する要求が強まる中で、連続鋳造用パウダーには、溶鋼中へ巻き込まれ難く、溶鋼を汚染（酸素供給）しない、という特性が求められるようになった。これら特性を満たすために具備すべき物性は、ａ）Ａｌ等の溶鋼中脱酸成分に還元されやすいＳｉＯ2 等の低級酸化物が少ない、すなわち高塩基度（高ＣａＯ／ＳｉＯ2 ）である、及び、ｂ）高粘度である、ことである。 In recent years, as the demand for steel cleaning has increased, the powder for continuous casting has been required to have a characteristic that it is difficult to get caught in molten steel and does not contaminate the molten steel (oxygen supply). The physical properties to be provided in order to satisfy these characteristics are: a) few low oxides such as SiO 2 that are easily reduced to deoxidized components in molten steel such as Al, that is, high basicity (high CaO / SiO 2 ). And b) high viscosity.
従来は、上記特性の中でも高粘度化が重要とされ、パウダー塩基度を低下させることにより高い粘度のパウダーを得ていた。例えば１３００℃における粘度が３〜１５ポアズの極低炭素鋼用モールドパウダーで、粘度を３ポアズ以上とすることで、モールドパウダーの巻き込みを防止するものである。なお、パウダーの粘度を上昇させるには、塩基度（ＣａＯ／ＳｉＯ2 ）を低下させ、ＳｉＯ2 のネットワークを強化することが一般に行われる。
しかしながら、パウダーの塩基度低下は、他方の具備すべき物性を犠牲にする。すなわち、低塩基度パウダーは、多く含まれるＳｉＯ2 がＡｌ等の溶鋼中脱酸元素により還元され、鋼に酸素供給（溶鋼を汚染）しやすいという問題がある。 However, the decrease in the basicity of the powder sacrifices the other physical property to be provided. That is, the low basicity powder has a problem that SiO 2 contained in a large amount is reduced by a deoxidizing element in molten steel such as Al, so that oxygen is easily supplied to the steel (contamination of molten steel).
上記問題は、高粘度の高塩基度パウダーを開発することにより解消される。例えば１３００℃における粘度が３〜８ポアズ、塩基度（ＣａＯ／ＳｉＯ2 ）が１．３以上３．０未満である連続鋳造用パウダーが提案されているが、高粘度かつ高塩基度パウダーの設計ノウハウに関する具体的な記述は無い。
また、高塩基度パウダーに結晶化調整剤としてＡｌ2 Ｏ3 を添加する方法が提案されているが、主たる結晶カスピダイン（Cuspidine ：３ＣａＯ・２ＳｉＯ2 ・ＣａＦ2 ）の析出安定性がＡｌ2 Ｏ3 添加の影響を受けることに関する記述は無い。
高塩基度パウダーの粘度上昇には両性酸化物であるＡｌ2 Ｏ3 等の添加が有効であるが、高塩基度パウダーに単にＡｌ2 Ｏ3 等の両性酸化物を添加すると、溶融パウダーが鋳型・凝固シェル間に流入し、形成するパウダーフィルム中への結晶析出が不安定となる。 The addition of amphoteric oxides such as Al 2 O 3 is effective for increasing the viscosity of high basicity powders. However, when amphoteric oxides such as Al 2 O 3 are simply added to the high basicity powders, the molten powder becomes the mold. -It flows between the solidified shells, and crystal precipitation in the powder film to be formed becomes unstable.
パウダーフィルム中に析出する結晶は、鋳型への抜熱を抑制し、凝固シェルを緩冷却化することにより凝固の均一性を高めるという重要な役割を果たしている。ゆえに、不安定な結晶析出は、シェルの不均一凝固を引き起こし、鋳片に縦割れ等の欠陥が生じる原因となる。或いは、鋳型温度が大きく変動しブレークアウト予知システムが誤作動するなど、操業性が悪化する。 Crystals deposited in the powder film play an important role of suppressing heat removal to the mold and increasing the uniformity of solidification by slowly cooling the solidified shell. Therefore, unstable crystal precipitation causes uneven solidification of the shell and causes defects such as vertical cracks in the slab. Alternatively, the operability deteriorates, for example, the mold temperature fluctuates greatly and the breakout prediction system malfunctions.
このように、従来技術においては、清浄鋼用の連続鋳造用パウダーに求められる高粘度と高塩基度（低ＳｉＯ2 ）という条件を同時に満たすパウダーが、実用に耐える結晶析出の安定性を併せ持つということができなかった。 Thus, in the prior art, a powder that simultaneously satisfies the conditions of high viscosity and high basicity (low SiO 2 ) required for powder for continuous casting for clean steel has the stability of crystal precipitation that can withstand practical use. I couldn't.
かかる問題を解消するべく、本発明者らは、特願２００２−０２８２１１において、溶融スラグの凝固時にゲーレナイト（Gehlenite ：２ＣａＯ・Ａｌ2 Ｏ3 ・ＳｉＯ2 ）、アケルマナイト（Akermanite：２ＣａＯ・ＭｇＯ・２ＳｉＯ2 ）、或いは、両者の全率固溶体であるメリライト（Melilite）を主な結晶組成として析出させる連続鋳造用パウダーを提案している。本発明者はその後の研究開発結果を反映し、上記提案したパウダーに対しＣａＯ／ＳｉＯ2 や凝固温度、粘度、ＴｉＯ2 農度、アルカリ金属酸化物（Ｎａ2 Ｏ＋Ｋ2 Ｏ＋Ｌｉ2 Ｏ）の範囲を調整すると共に、Ｆ濃度の下限値、Ａｌ2 Ｏ3 とＭｇＯとの濃度和、ＦｅＯとＭｎＯとの濃度和、Ｓ濃度や膨張性黒鉛添加について新たに具体的に規定した本発明を成立するに到った。 To solve such a problem, the present inventors have found that in Japanese Patent Application No. 2002-028211, gehlenite during solidification of the molten slag (Gehlenite: 2CaO · Al 2 O 3 · SiO 2), Akerumanaito (Akermanite: 2CaO · MgO · 2SiO 2 Or a powder for continuous casting in which melilite, which is a solid solution of both, is precipitated as a main crystal composition. The present inventor reflected the results of subsequent research and development, and added CaO / SiO 2 , solidification temperature, viscosity, TiO 2 agricultural strength, and alkali metal oxide (Na 2 O + K 2 O + Li 2 O) ranges to the proposed powder. In addition to the adjustment, the lower limit of the F concentration, the sum of the concentrations of Al 2 O 3 and MgO, the sum of the concentrations of FeO and MnO, the S concentration, and the addition of expansive graphite are newly established. Arrived.
本発明者は他に、上述の先に提案したパウダーから派生したものとして、特願２００２−０７０２７６を提案している。このパウダーは、一旦溶融した後、凝固したパウダーフィルム中に析出する結晶の内、１種類の「主な結晶」の析出量が他種結晶の析出量の２倍以上であることを（請求項１）、また、一旦溶融した後凝固したパウダーフィルム中に析出する結晶の内、少なくとも２種類の結晶組が全率固溶体を形成し実質的に１種類の「主な結晶」をなすこと（請求項３）を、また、Ｆ濃度が４質量％以下であること（請求項６）を、また、「主な結晶」がアケルマナイト、ゲーレナイト、メリライト等のうちのいずれか１種であること（請求項７）を、それぞれ特徴とする連続鋳造用パウダーである。しかしながら、これらのパウダーは、結晶析出或いは晶出が安定化する、より一般的な条件について規定したパウダーの一部を成すものであり、本発明とは異なる発明である。 In addition, the present inventor has proposed Japanese Patent Application No. 2002-070276 as being derived from the previously proposed powder. After the powder is once melted, the amount of precipitation of one kind of “main crystals” among the crystals precipitated in the solidified powder film is more than twice the amount of precipitation of other types of crystals. 1) In addition, among the crystals precipitated in the powder film which has been once melted and solidified, at least two types of crystals form a complete solid solution to form substantially one type of “main crystals” (claims) Item 3), the F concentration being 4% by mass or less (Claim 6), and the “main crystals” being any one of akermanite, gehlenite, melilite, etc. Item 7) is a powder for continuous casting characterized by each. However, these powders are part of powders that are defined for more general conditions in which crystal precipitation or crystallization is stabilized, and are different from the present invention.
解決しようとする問題点は、高粘度および高塩基度（低ＳｉＯ2 ）、という鋼を清浄に連続鋳造するためのパウダーに求められる特性を同時に満たしつつ、パウダーフィルム中への安定な結晶析出をも同時に実現できない点である。 The problem to be solved is to achieve stable crystal precipitation in the powder film while simultaneously satisfying the properties required for powder for continuous casting of steel with high viscosity and high basicity (low SiO 2 ). Cannot be realized at the same time.
本発明は、アケルマナイト、ゲーレナイト、或いは、両者の全率固溶体であるメリライトを、溶融スラグ凝固時に主な結晶組成として析出し、ＣａＯ濃度とＳｉＯ2 濃度の比、ＣａＯ／ＳｉＯ2 が１．０〜１．５、Ａｌ2 Ｏ3 とＭｇＯの濃度合計が１５〜２７質量％、Ｎａ2 ＯとＬｉ2 ＯとＫ2 Ｏの濃度合計が１〜１３質量％、Ｆ濃度が１〜５質量％、ＦｅＯとＭｎＯの濃度合計が３質量％以下、Ｓ濃度が０．５質量％以下、凝固温度が１１００℃〜１２６０℃、１３００℃における粘度が０．２〜１．３Ｐａ・ｓであることを最も主要な特徴としている。 In the present invention, akermanite, gehlenite, or melilite, which is a solid solution of both, is precipitated as a main crystal composition during solidification of molten slag, and the ratio of CaO concentration to SiO 2 concentration, CaO / SiO 2 is 1.0 to 1.5, the total concentration of Al 2 O 3 and MgO is 15 to 27% by mass, the total concentration of Na 2 O, Li 2 O and K 2 O is 1 to 13% by mass, the F concentration is 1 to 5% by mass, It is most preferable that the total concentration of FeO and MnO is 3% by mass or less, the S concentration is 0.5% by mass or less, the solidification temperature is 1100 ° C. to 1260 ° C., and the viscosity at 1300 ° C. is 0.2 to 1.3 Pa · s. Main features.
本発明によれば、粘度が高く、塩基度が高く、パウダーフィルムの結晶化が安定しているという、鋼を清浄に連続鋳造することができるモールドパウダーが具備すべき特性を併せ持つことが可能である。 According to the present invention, it is possible to have the characteristics to be possessed by a mold powder capable of continuously casting clean steel, such as high viscosity, high basicity, and stable crystallization of a powder film. is there.
高塩基度パウダーの粘度を上げようとして両性酸化物であるＡｌ2 Ｏ3 等を添加すると、鋳型内で溶融スラグとなったモールドパウダーが鋳型・凝固シェル間に流入し、形成するパウダーフィルム中における結晶析出が不安定となる。この問題は、多量に含まれるＡｌ2 Ｏ3 等の両性酸化物がパウダーフィルム中に析出する代表的結晶であるカスピダインの析出を阻害していることに起因していると考えた。 When Al 2 O 3 that is an amphoteric oxide is added to increase the viscosity of the high basicity powder, the mold powder that has become molten slag in the mold flows between the mold and the solidified shell, and in the powder film that forms. Crystal precipitation becomes unstable. This problem was thought to be due to the fact that amphoteric oxides such as Al 2 O 3 contained in a large amount hindered the precipitation of caspodyne, which is a typical crystal precipitated in the powder film.
本発明者は、Ａｌ2 Ｏ3 を多く含有するモールドパウダーのフィルム中結晶析出を安定させるには、Ａｌ2 Ｏ3 を構成成分に持つ結晶を析出させる他にないと考え、Ａｌ2 Ｏ3 を含む適当な結晶を探した。適当な結晶とは、塩基度（ＣａＯ／ＳｉＯ2 ）が１．０以上であり、融点が鋼の融点より２００℃程度の低い範囲、すなわち１３００℃〜１５５０℃程度であり、構成成分が工業的に安く入手できる結晶である。その結果、発明者はゲーレナイトとアケルマナイトとの全率固溶体であるメリライト（表１参照）を見出した。 The present inventor has, in order to stabilize the film during crystallization of the mold powder containing a large amount of Al 2 O 3, not considered in addition to precipitate crystals having a component of Al 2 O 3, the Al 2 O 3 Searched for suitable crystals to contain. Appropriate crystals have a basicity (CaO / SiO 2 ) of 1.0 or more, a melting point of about 200 ° C. lower than the melting point of steel, that is, about 1300 ° C. to 1550 ° C., and the constituent components are industrial. It is a crystal that can be obtained cheaply. As a result, the inventor found melilite (see Table 1), which is a solid solution of gelenite and akermanite.
次に、メリライトを安定して析出させることができるモールドパウダー組成に調整した。結晶は、その純組成に近い溶融スラグからは安定して析出するので、例えば、ゲーレナイトとアケルマナイトとが５０：５０の割合で固溶したメリライト、すなわち、表１中のゲーレナイトとアケルマナイトとの中間組成であるＣａＯ／ＳｉＯ2 が１．２４、Ａｌ2 Ｏ3 が１８．６質量％、ＭｇＯが７．３５質量％を主成分とし、それに物性調整上必要なアルカリ金属酸化物（Ｎａ2 Ｏ等）やＦなどを加えた組成を基材とする手法で以下の本発明の組成を決定した。 Next, it adjusted to the mold powder composition which can deposit melilite stably. Since crystals are stably precipitated from molten slag close to its pure composition, for example, melilite in which gehlenite and akermanite are dissolved in a ratio of 50:50, that is, an intermediate composition of gehlenite and akermanite in Table 1 CaO / SiO 2 is 1.24%, Al 2 O 3 is 18.6% by mass, MgO is 7.35% by mass, and alkali metal oxides (Na 2 O, etc.) necessary for adjusting the physical properties thereof. The following composition of the present invention was determined by a method using a composition to which F and F were added as a base material.
すなわち、第１の本発明の鋼の連続鋳造用モールドパウダーは、アケルマナイト、ゲーレナイト、或いは、両者の全率固溶体であるメリライトを、溶融スラグ凝固時に主な結晶組成として析出し、ＣａＯ濃度とＳｉＯ2 濃度の比、ＣａＯ／ＳｉＯ2 を１．０〜１．５、Ａｌ2 Ｏ3 とＭｇＯの濃度合計を１５〜２７質量％、Ｎａ2 ＯとＬｉ2 ＯとＫ2 Ｏの濃度合計を１〜１３質量％、Ｆ濃度を１〜５質量％、ＦｅＯとＭｎＯの濃度合計を３質量％以下、Ｓ濃度を０．５質量％以下、凝固温度を１１００℃〜１２６０℃、１３００℃における粘度を０．２〜１．３Ｐａ・ｓとしたものである。 That is, the mold powder for continuous casting of steel according to the first aspect of the present invention precipitates akermanite, gehlenite, or melilite, which is a solid solution of both, as a main crystal composition during solidification of molten slag, and the CaO concentration and SiO 2 Concentration ratio, CaO / SiO 2 1.0 to 1.5, Al 2 O 3 and MgO total concentration 15 to 27% by mass, Na 2 O, Li 2 O and K 2 O total concentration 1 to 13 mass%, F concentration is 1-5 mass%, total concentration of FeO and MnO is 3 mass% or less, S concentration is 0.5 mass% or less, solidification temperature is 1100 ° C to 1260 ° C, viscosity at 1300 ° C is 0 2 to 1.3 Pa · s.
本発明において、ＣａＯ／ＳｉＯ2 を１．０〜１．５としたのは、１．０未満ではＳｉＯ2 活量が高くなり、低級酸化物であるＳｉＯ2 による溶鋼汚染が大きくなるためである。一方、ＣａＯ／ＳｉＯ2 が１．５を超えると、凝固温度が高くなり過ぎて操業に適さないためである。 In the present invention, the reason why CaO / SiO 2 is set to 1.0 to 1.5 is that if it is less than 1.0, the SiO 2 activity is high, and the contamination of molten steel by SiO 2 which is a lower oxide increases. . On the other hand, if CaO / SiO 2 exceeds 1.5, the solidification temperature becomes too high and it is not suitable for operation.
また、Ａｌ2 Ｏ3 とＭｇＯとの濃度合計を１５〜２７質量％としたのは、メリライトがＡｌ2 Ｏ3 あるいはＭｇＯを主な組成のひとつとして含む結晶であることから、メリライトの安定析出にはＡｌ2 Ｏ3 とＭｇＯとの濃度合計が１５質量％必要であるためである。しかしながら、Ａｌ2 Ｏ3 とＭｇＯとの濃度合計が２７質量％を超えると、凝固温度が高くなり過ぎて適当でないので、２７質量％以下とした。 The reason why the total concentration of Al 2 O 3 and MgO is 15 to 27% by mass is that the melilite is a crystal containing Al 2 O 3 or MgO as one of the main compositions. This is because 15% by mass of the total concentration of Al 2 O 3 and MgO is necessary. However, if the total concentration of Al 2 O 3 and MgO exceeds 27% by mass, the solidification temperature becomes too high to be appropriate, so the content was set to 27% by mass or less.
また、Ｎａ2 ＯとＬｉ2 ＯとＫ2 Ｏとの濃度合計を１〜１３質量％としたのは、これが１質量％以下では、パウダーフィルム中の液相が不足しやすくなり、鋳型内潤滑性が悪化するためである。逆に１３質量％を超えると、凝固温度が低下しすぎたり、アルカリ金属酸化物を含む他の結晶が析出したり、これらアルカリ金属酸化物がＳｉＯ2 と反応して約８００℃で生成する液相がバインダとなって鋳型内のパウダーの焼結が進行し、流動性が悪化するなど、操業に悪影響を及ぼすからである。 Moreover, the total concentration of Na 2 O, Li 2 O and K 2 O was set to 1 to 13% by mass. If this is 1% by mass or less, the liquid phase in the powder film tends to be insufficient, and lubrication within the mold is performed. This is because sex deteriorates. On the other hand, if it exceeds 13% by mass, the solidification temperature is too low, other crystals containing alkali metal oxides are precipitated, or these alkali metal oxides react with SiO 2 to form at about 800 ° C. This is because the phase becomes a binder and the sintering of the powder in the mold proceeds and the fluidity is deteriorated.
さらには、肥大化したスラグベアが、鋳型のオシレーション（上下振動）に伴い凝固シェル先端を押し込むことで局部的なメニスカスの乱れを引き起こし、パウダー巻込欠陥が発生する。Ｎａ2 ＯとＬｉ2 ＯとＫ2 Ｏとの濃度合計は２〜１０質量％であればさらに好ましい。さらに、鋳型断面の小さいビレットの連続鋳造では、鋳型壁から庇状に成長したパウダー焼結体であるスラグべアが鋳型表面を覆って操業を阻害しやすいので、Ｎａ2 ＯとＬｉ2 ＯとＫ2 Ｏとの濃度合計は４質量％に上限値を抑えることが望ましい。 Furthermore, when the enlarged slag bear pushes the tip of the solidified shell with the oscillation of the mold (vertical vibration), local disturbance of the meniscus is caused and a powder entrainment defect occurs. More preferably, the total concentration of Na 2 O, Li 2 O and K 2 O is 2 to 10% by mass. Furthermore, in continuous casting of a billet with a small mold section, a slag bear, which is a powder sintered body grown like a bowl from the mold wall, covers the mold surface and tends to hinder the operation, so Na 2 O and Li 2 O The total concentration with K 2 O is desirably 4% by mass and the upper limit is preferably suppressed.
Ｆ濃度を１〜５質量％としたのは、これが１質量％未満では凝固温度が高くなり過ぎ、鋳型内潤滑性が悪化するためである。但し、５質量％を超えると、パウダーフィルム中において主たる結晶であるメリライトと競合してＦを含むカスピダインが多く析出するようになり、互いの結晶界面の不整合性に起因する融点低下を引き起こし、結晶析出が不安定になるので好ましくないからである。Ｆ濃度は１．５〜４質量％の範囲内であればさらに望ましい。 The reason why the F concentration is set to 1 to 5% by mass is that if it is less than 1% by mass, the solidification temperature becomes too high and the in-mold lubricity deteriorates. However, when it exceeds 5% by mass, a large amount of caspidyne containing F competes with melilite, which is the main crystal in the powder film, to cause a melting point decrease due to inconsistency of the mutual crystal interface, This is because crystal precipitation becomes unstable, which is not preferable. The F concentration is more preferably in the range of 1.5 to 4% by mass.
これらアルカリ金属酸化物とＦ濃度との比は、カスピダイン析出を抑制するという観点からは、溶融スラグ中においてアルカリ金属がＦと優先的に結合し（例えばＮａＦとなり）、カスピダインの析出を抑制するという現象を活用するべく、含有するＦと等モル濃度以上のアルカリ金属を含有するよう調整することがより好ましい。 The ratio between the alkali metal oxide and the F concentration is that, from the viewpoint of suppressing caspidine precipitation, the alkali metal preferentially binds to F (for example, NaF) in the molten slag, thereby suppressing caspidyne precipitation. In order to utilize the phenomenon, it is more preferable to adjust so as to contain an alkali metal at an equimolar concentration or more with F contained.
ＦｅＯとＭｎＯとの濃度合計を３質量％以下にするのは、ＳｉＯ2 よりもさらに低級、すなわち酸素を放出しやすいＦｅＯ或いはＭｎＯの濃度が高いと、高塩基度（高ＣａＯ／ＳｉＯ2 ）化し、溶鋼汚染を低減する効果が損なわれてしまうからである。ＦｅＯとＭｎＯとの濃度合計は２質量％以下であればさらに好ましい。 The reason why the total concentration of FeO and MnO is 3% by mass or less is lower than that of SiO 2 , that is, when the concentration of FeO or MnO that easily releases oxygen is high, the basicity (high CaO / SiO 2 ) is increased. This is because the effect of reducing molten steel contamination is impaired. More preferably, the total concentration of FeO and MnO is 2% by mass or less.
Ｓ濃度を０．５質量％以下とするのは、パウダー中のＳ濃度が高い場合には、界面活性元素であるＳがパウダー溶融スラグ層と溶鋼との界面に集まって界面張力を低下させ、パウダーが溶鋼中に巻き込まれ易くなるからである。Ｓ濃度は０．３質量％以下であればさらに好ましい。 The S concentration is 0.5% by mass or less when the S concentration in the powder is high, the surface active element S gathers at the interface between the powder molten slag layer and the molten steel to reduce the interfacial tension, This is because the powder is easily caught in the molten steel. The S concentration is more preferably 0.3% by mass or less.
凝固温度を１１００℃〜１２６０℃とするのは、凝固温度が１１００℃未満であると、凝固シェルと鋳型との間隙に位置するパウダーフィルムが凝固しにくくなり、パウダーフィルム中の結晶析出が不足して、パウダーフィルムを介した凝固シェルから鋳型への輻射熱伝導が増加し、凝固シェルを急激に冷却しすぎて縦割れ等の割れ性欠陥が鋳片表面に生じ易くなるからである。逆に凝固温度が１２６０℃を超えると、パウダーフィルムの凝固が進行しすぎて液相が不足し、潤滑性が悪化する結果、凝固シェルの破断等のトラブルを生じるので好ましくないからである。 The solidification temperature is set to 1100 ° C. to 1260 ° C. If the solidification temperature is less than 1100 ° C., the powder film located in the gap between the solidification shell and the mold becomes difficult to solidify, and crystal precipitation in the powder film is insufficient. This is because radiant heat conduction from the solidified shell to the mold through the powder film increases, and the solidified shell is rapidly cooled too much, so that cracking defects such as vertical cracks are likely to occur on the surface of the slab. Conversely, if the solidification temperature exceeds 1260 ° C., the solidification of the powder film proceeds excessively, the liquid phase becomes insufficient, and the lubricity deteriorates, resulting in problems such as breakage of the solidified shell, which is not preferable.
一般に凝固初期の収縮が大きな鋼種ほど縦割れ等の割れ性欠陥を鋳片表面に生じ易く、逆に凝固初期の収縮が小さな鋼種ほど凝固シェルと鋳型との間隙が小さくなるので、パウダーフィルムが薄くなり、潤滑性が悪化し易い。ゆえに凝固温度は１１００℃〜１２６０℃の間で、凝固初期の収縮が大きな鋼種では高めに、凝固初期の収縮が小さな鋼種では低めに調整するとさらに良い結果が得られる。 In general, steel types with large shrinkage at the beginning of solidification tend to cause cracking defects such as vertical cracks on the surface of the slab. Conversely, steel types with small shrinkage at the beginning of solidification have a smaller gap between the solidified shell and the mold, so the powder film is thinner. Therefore, lubricity tends to deteriorate. Therefore, a better result can be obtained by adjusting the solidification temperature between 1100 ° C. and 1260 ° C. and adjusting it higher for a steel type having a large initial shrinkage and lower for a steel type having a small initial shrinkage.
１３００℃における粘度を０．２〜１．３Ｐａ・ｓとするのは、粘度が０．２Ｐａ・ｓ未満の場合には粘度が低すぎるので、パウダー溶融スラグが溶鋼中へ巻き込まれ易くなり、一方、粘度が１．３Ｐａ・ｓを超えると粘度が高すぎて潤滑性が悪化するからである。粘度は０．３〜１．０Ｐａ・ｓであればさらに好ましい。 The reason why the viscosity at 1300 ° C. is 0.2 to 1.3 Pa · s is that the viscosity is too low when the viscosity is less than 0.2 Pa · s, so that the powder molten slag is likely to be caught in the molten steel, This is because if the viscosity exceeds 1.3 Pa · s, the viscosity is too high and the lubricity deteriorates. More preferably, the viscosity is 0.3 to 1.0 Pa · s.
上記に加え、凝固温度を低下させる成分調整としてＴｉＯ2 を１〜８質量％含有させることも有効である。ＴｉＯ2 濃度が１質量％未満では、凝固温度の調整効果が小さく、一方、８質量％を超えると、単体で１９８０℃と高い融点を持つペロブスカイト（Perovskite：ＣａＯ・ＴｉＯ2 ）が多く析出して凝固温度が上昇に転じるので好ましくないからである。さらに望ましいＴｉＯ2 含有量は２〜６質量％である。これが、第２の本発明である。 In addition to the above, it is also effective to contain 1 to 8% by mass of TiO 2 as component adjustment for lowering the solidification temperature. When the TiO 2 concentration is less than 1% by mass, the effect of adjusting the solidification temperature is small. On the other hand, when it exceeds 8% by mass, a large amount of perovskite (Perovskite: CaO · TiO 2 ) having a high melting point of 1980 ° C. is precipitated. This is because the coagulation temperature starts to rise. A more desirable TiO 2 content is 2 to 6% by mass. This is the second aspect of the present invention.
モールドパウダーは、上述のように成分調整した基材に、滓化速度調整用の骨材としてカーボンブラックやコークス粉などのカーボンを加えたものが一般に用いられる。この骨材として膨張性黒鉛を１〜５質量％添加すると、鋳型内におけるパウダーの焼結が進行せず、特に小断面鋳型を使用したビレット製造の連続鋳造で問題となるスラグベアの成長が抑制されることが判明した。あるいは、肥大化したスラグベアが、鋳型のオシレーション（上下振動）に伴い凝固シェル先端を押し込むことで、局部的なメニスカスの乱れを引き起こし、パウダー巻込欠陥を発生させることも防止できる。 The mold powder is generally obtained by adding carbon such as carbon black or coke powder as an aggregate for adjusting the hatching speed to the base material whose components are adjusted as described above. When 1-5% by mass of expansive graphite is added as the aggregate, the powder does not sinter in the mold, and the growth of slag bear, which is a problem in continuous casting of billets using a small-section mold, is suppressed. Turned out to be. Alternatively, the enlarged slag bear pushes the tip of the solidified shell with the mold oscillation (vertical vibration), thereby causing local meniscus disturbance and preventing powder entrainment defects.
膨張性黒鉛とは、黒鉛の積層構造の間に、加熱時にガスを発生する硫酸等の物質を含侵させたもので、加熱すると数十倍から数百倍に体積が膨張する。膨張性黒鉛は、１質量％未満では添加効果が無く、５質量％を超えて添加すると鋳型内で膨張した黒鉛が体積の多くを占めるようになり、パウダーの流動性が悪化する。これが、第３の発明である。膨張性黒鉛は、鋳型断面が小さくスラグベアの成長が問題となる場合や、Ｎａ2 ＯとＬｉ2 ＯとＫ2 Ｏとの濃度合計が大きくパウダーが焼結し易い場合には、添加量を２乃至３質量％以上に調整することが望ましい。 Expandable graphite is a structure in which a layered structure of graphite is impregnated with a substance such as sulfuric acid that generates a gas upon heating. When heated, the volume expands several tens to several hundreds. If the expandable graphite is less than 1% by mass, there is no effect of addition, and if it is added in excess of 5% by mass, the expanded graphite in the mold occupies much of the volume, and the fluidity of the powder deteriorates. This is the third invention. In the case of expansive graphite, if the mold cross section is small and slag bear growth is a problem, or if the total concentration of Na 2 O, Li 2 O and K 2 O is large and the powder is easy to sinter, the addition amount is 2 It is desirable to adjust to 3% by mass or more.
なお、パウダー組成は上述のように金属酸化物、Ｆ、及びカーボン濃度として表している。このうち、金属酸化物で表した組成は、パウダー原料における該当金属の総濃度を酸化物濃度に換算して表したものである。例えば、ＣａＯとは、ＣａＯやＣａＦ2 に含まれる総Ｃａ濃度のＣａＯ濃度換算値であり、Ｎａ2 Ｏとは、Ｎａ2 Ｏ、ＮａＦ、Ｎａ2 ＣＯ3 に含まれる総Ｎａ濃度のＮａ2 Ｏ濃度換算値と言った具合である。また、Ｆはパウダー原料におけるＦ化合物、例えばＣａＦ2 、ＮａＦ、ＡＩＦ3 に含まれる総Ｆ濃度である。カーボンは、骨材として基材に添加される固体のカーボンを指し、Ｎａ2 ＣＯ3 等の炭酸塩中のカーボンは含まない。 The powder composition is expressed as metal oxide, F, and carbon concentration as described above. Among these, the composition represented by the metal oxide represents the total concentration of the corresponding metal in the powder raw material converted into the oxide concentration. For example, the CaO, CaO and a CaO concentration conversion value of the total Ca concentration in the CaF 2, and Na 2 O, Na 2 O, NaF, total Na concentration of Na 2 O contained in the Na 2 CO 3 This is the concentration conversion value. F is the total F concentration contained in F compounds such as CaF 2 , NaF and AIF 3 in the powder raw material. Carbon refers to solid carbon added to the base material as an aggregate, and does not include carbon in carbonates such as Na 2 CO 3 .
溶融スラグ凝固時に主に析出する結晶組成とは、鋳型から回収したパウダーフィルムや、同組成の溶融スラグを徐冷した固形物を、Ｘ線回折試験に供し、回折ピークが最も高い結晶組成を調査することにより明らかとなる。本発明においては、同組成の溶融スラグを１００〜４００℃／ｈｒで徐冷した固形物を用いて調査した。 The crystal composition that mainly precipitates during solidification of molten slag is to examine the crystal composition with the highest diffraction peak by subjecting the powder film recovered from the mold and solids obtained by slow cooling of molten slag of the same composition to the X-ray diffraction test. It becomes clear by doing. In this invention, it investigated using the solid substance which annealed the molten slag of the same composition at 100-400 degreeC / hr.
アケルマナイトとゲーレナイトの結晶構造が酷似している結果、両者がメリライトという全率固溶体を形成するということから、析出結晶がアケルマナイトかゲーレナイトかメリライトか厳密に区別することは難しい。ゆえに本発明においてアケルマナイト、ゲーレナイト、またはメリライトが析出する場合、パウダー中のＭｇＯ含有量がＡｌ2 Ｏ3 含有量に対して３倍以上の場合にアケルマナイト、パウダー中のＡｌ2 Ｏ3 含有量がＭｇＯ含有量の３倍以上の場合にゲーレナイト、その他の場合にはメリライトが析出していると便宜的に定義し、以下の実施例を説明している。 As a result of the crystal structures of akermanite and gehlenite being very similar, both form a solid solution of melilite, so it is difficult to strictly distinguish whether the precipitated crystal is akermanite, gehlenite or melilite. Therefore Akerumanaito In the present invention, gehlenite or if melilite is precipitated, Akerumanaito when MgO content in the powder is more than 3 times the content of Al 2 O 3, content of Al 2 O 3 is MgO in the powder, For convenience, it is defined that gehlenite is precipitated when the content is 3 times or more, and melilite is precipitated in other cases, and the following examples are described.
下記表２及び表３のＡ〜Ｆは本発明による実施例である。 A to F in Table 2 and Table 3 below are examples according to the present invention.
実施例Ａは、第１の本発明を満たすモールドパウダーである。塩基度（ＣａＯ／ＳｉＯ2 ）及び粘度が十分に高くＳ濃度も低いので、パウダー巻込欠陥発生指数が良好であり、Ａｌ2 Ｏ3 とＭｇＯとの濃度合計が適正でＦ濃度が低くＮａ2 ＯとＬｉ2 ＯとＫ2 Ｏとの濃度合計が上限値を超えていないことに加え、凝固温度が下限値（１１００℃）以上であるので、アケルマナイトを溶融スラグ凝固時の主な結晶組成として安定して析出する。また、Ｎａ2 ＯとＬｉ2 ＯとＫ2 Ｏとの濃度合計が下限値以上であり、凝固温度が上限値（１２６０℃）を超えていないので、潤滑性も良好である。このように、実施例Ａは、第１の本発明が必要な要件を満たしているので、良好な鋳片品質及び操業性を実現できる。 Example A is a mold powder that satisfies the first aspect of the present invention. Since the basicity (CaO / SiO 2 ) and viscosity are sufficiently high and the S concentration is low, the powder entrainment defect occurrence index is good, the total concentration of Al 2 O 3 and MgO is appropriate, the F concentration is low, and Na 2 In addition to the total concentration of O, Li 2 O, and K 2 O not exceeding the upper limit, the solidification temperature is not lower than the lower limit (1100 ° C.), so that akermanite is used as the main crystal composition during molten slag solidification. Precipitates stably. Moreover, since the total concentration of Na 2 O, Li 2 O and K 2 O is not less than the lower limit and the solidification temperature does not exceed the upper limit (1260 ° C.), the lubricity is also good. Thus, since Example A satisfies the requirements of the first aspect of the present invention, good slab quality and operability can be realized.
実施例Ｅ及びＧは、第１及び第２の本発明が必要な要件を満たすモールドパウダーである。これらは第１の本発明が必要な要件を満たすので、実施例Ａと同様に優れた鋳片品質及び操業性を実現できた。さらに第２の本発明が必要な要件をも満たす、すなわちＴｉＯ2 を適正量含有するので、凝固温度を下げることもできた。 Examples E and G are mold powders that satisfy the requirements of the first and second aspects of the present invention. Since these satisfy the requirements of the first aspect of the present invention, excellent slab quality and operability can be realized as in Example A. Furthermore, since the second present invention satisfies the necessary requirements, that is, it contains an appropriate amount of TiO 2 , the solidification temperature can be lowered.
一般に塩基度（ＣａＯ／ＳｉＯ2 ）を高めると凝固温度が高くなるので、ＴｉＯ2 添加により凝固温度を下げることができれば、ＴｉＯ2 を添加しない場合に比べて高塩基度化（高ＣａＯ／ＳｉＯ2 化）し易くなる。ＴｉＯ2 添加の効果により実施例Ｅ及びＧは実施例Ａよりも容易に高塩基度化することができた。高塩基度化の結果、パウダー巻込欠陥発生指数は実施例Ａに比べさらに優良となる。 Since generally the solidification temperature increase basicity (CaO / SiO 2) is higher, if it is possible to lower the freezing temperature by TiO 2 addition, compared with the case of no addition of TiO 2 high basicity (higher CaO / SiO 2 ). Due to the effect of addition of TiO 2, Examples E and G could be made more basic than Example A. As a result of the increase in basicity, the powder entrainment defect occurrence index becomes even better than in Example A.
実施例Ｂ、Ｃ、Ｄ、Ｆは、第１〜第３の本発明が必要な要件満たすモールドパウダーである。これらは第１及び第２の本発明が必要な要件を満たすので、実施例Ｅ及びＧ同様に、優良な鋳片品質及び操業性を実現する。さらに、第３の本発明が必要な要件をも満たす、すなわち膨張性黒鉛を適正量添加したので、小断面の連続鋳造機でのスラグベア肥大による操業阻害や、肥大化したスラグベアが鋳型のオシレーション（上下振動）に伴って、凝固シェル先端を押し込むことで局部的なメニスカスの乱れを引き起こし発生するパウダー巻込欠陥を効果的に防止できる。 Examples B, C, D, and F are mold powders that satisfy the requirements of the first to third aspects of the present invention. Since these satisfy the requirements of the first and second aspects of the present invention, excellent slab quality and operability are realized as in Examples E and G. Furthermore, since the third aspect of the present invention satisfies the necessary requirements, that is, an appropriate amount of expansive graphite is added, the operation is hindered due to the enlargement of the slag bear in the continuous casting machine with a small cross section, and the enlarged slag bear is the oscillation of the mold. Along with (vertical vibration), by pushing in the tip of the solidified shell, it is possible to effectively prevent a powder entrainment defect caused by local disturbance of the meniscus.
一方、表２及び表３のＨ〜Ｎは、表２に＊印を付したものが、本発明の範囲を外れた比較例を示したものである。
比較例Ｈは、凝固温度が本発明の上限値より高いため潤滑性が悪く実操業に耐えない例である。
On the other hand, H to N in Table 2 and Table 3 show comparative examples in which the mark * in Table 2 is out of the scope of the present invention.
Comparative Example H is an example in which the solidification temperature is higher than the upper limit of the present invention, so that the lubricity is poor and the actual operation cannot be endured.
また、比較例Ｉ及びＪは、Ａｌ2 Ｏ3 とＭｇＯとの濃度合計が本発明の下限値よりも小さいので、カスピダインが主な結晶として析出した例である。比較例ＩではＦ濃度が本発明の上限値より高いこともカスピダインが析出する要因である。上記のＡｌ2 Ｏ3 とＭｇＯとの濃度合計が小さいことに加えて、比較例Ｉのように更にＡｌ2 Ｏ3 濃度が１０質量％と高い場合や、比較例ＪのようにＦ濃度が２質量％と低い場合には、たとえ主な結晶としてカスピダインが析出しても、析出が不安定になり易い。 Comparative Examples I and J are examples in which caspidine was precipitated as main crystals because the total concentration of Al 2 O 3 and MgO was smaller than the lower limit of the present invention. In Comparative Example I, the fact that the F concentration is higher than the upper limit of the present invention is also a factor for the precipitation of cuspidyne. In addition to the small concentration of Al 2 O 3 and MgO, when the Al 2 O 3 concentration is as high as 10% by mass as in Comparative Example I, or when the F concentration is 2 as in Comparative Example J, When the content is as low as mass%, the precipitation is likely to be unstable even if caspidine is precipitated as the main crystal.
すなわち、凝固シェルと鋳型との間隙に位置するパウダーフィルム中の結晶析出の不安定さに起因して、パウダーフィルムを介した凝固シェルから鋳型への輻射熱伝導の変動が増大するので、凝固シェルの成長が不均等になり、鋳片表面に割れ性欠陥が発生し易くなるという問題が生じる。 In other words, due to the instability of crystal precipitation in the powder film located in the gap between the solidified shell and the mold, the variation in radiant heat conduction from the solidified shell to the mold via the powder film increases. There arises a problem that the growth becomes uneven and cracking defects are likely to occur on the surface of the slab.
また、比較例Ｋは、Ａｌ2 Ｏ3 とＭｇＯとの濃度合計が本発明の下限値よりも小さく、ＴｉＯ2 濃度が２０．０質量％と過度に高いので、チタナイト（Titanite：ＣａＯ・ＳｉＯ2 ・ＴｉＯ2 ）が主な結晶として析出した例である。この場合、チタナイトの他にカスピダインやペロブスカイトが競合して析出し、異種結晶界面における大幅な融点低下に起因して結晶析出が不安定となり、比較例Ｉ及びＪと同様に鋳片表面に割れ性欠陥が発生し易くなるという問題が生じる。 In Comparative Example K, since the total concentration of Al 2 O 3 and MgO is smaller than the lower limit of the present invention and the TiO 2 concentration is excessively high at 20.0% by mass, titanite (Titanite: CaO · SiO 2). This is an example in which TiO 2 ) is precipitated as main crystals. In this case, caspidyne and perovskite, in addition to titanite, compete and precipitate, resulting in unstable crystal precipitation due to a significant decrease in melting point at the interface between different crystals, and cracking on the slab surface as in Comparative Examples I and J. There arises a problem that defects are likely to occur.
比較例Ｌは、主な結晶としてメリライトが析出するものの、Ｎａ2 ＯとＬｉ2 ＯとＫ2 Ｏとの濃度合計が１質量％未満と本発明の下限値よりも小さいので、鋳型内における潤滑性が悪化する例である。加えて、ＦｅＯ＋ＭｎＯ濃度が高いので、溶鋼汚染が大きい例である。 In Comparative Example L, melilite precipitates as main crystals, but the total concentration of Na 2 O, Li 2 O, and K 2 O is less than 1% by mass, which is smaller than the lower limit of the present invention. This is an example of worsening sex. In addition, since the FeO + MnO concentration is high, molten steel contamination is an example.
比較例Ｍ及びＮは、塩基度すなわちＣａＯ濃度とＳｉＯ2 濃度との比ＣａＯ／ＳｉＯ2 が１．０未満と本発明の下限値よりも小さいので、溶鋼汚染が大きいという問題を有する。加えて比較例Ｍはパウダー中のＳ濃度が本発明の上限値よりも高いので溶鋼中への巻き込みが発生しやすい。 Comparative Examples M and N have a problem that the contamination of molten steel is large because the basicity, that is, the ratio CaO / SiO 2 between the CaO concentration and the SiO 2 concentration is less than 1.0 and lower than the lower limit of the present invention. In addition, in Comparative Example M, the S concentration in the powder is higher than the upper limit of the present invention, so that the entrainment in the molten steel is likely to occur.
本発明の効果を実証するべく、以下のように実機において比較実験を行った。
まず、実施例Ｂと比較例Ｎとを用い、鋳型径がφ３１０ｍｍの丸ビレツト連続鋳造機において０．２質量％Ｃ−１．３質量％Ｍｎのアルミ脱酸普通鋼を、鋳型内を電磁攪拌しつつ引抜速度１．４ｍ／ｍｉｎで鋳造し、鋳造したビレットをシームレス製管に供し、製品パイプにおけるパウダー巻込欠陥発生率を比較した。
In order to verify the effect of the present invention, a comparative experiment was performed on an actual machine as follows.
First, using Example B and Comparative Example N, 0.2 mass% C-1.3 mass% Mn aluminum deoxidized ordinary steel was used in a round billet continuous casting machine having a mold diameter of 310 mm, and the inside of the mold was electromagnetically stirred. While casting at a drawing speed of 1.4 m / min, the cast billet was used for seamless pipe making, and the occurrence rate of powder entrainment defects in the product pipe was compared.
その結果、パウダー巻込欠陥発生率は、比較例Ｎを用いた鋳片から製造したパイプに対し実施例Ｂを用いたものでは、１／６に軽減する効果が確認された。また、実施例Ｂと比較例Ｉとを用い、鋳型径がφ２２５ｍｍの丸ビレット連続鋳造において０．２質量％Ｃ−０．６質量％Ｍｎのアルミ脱酸普通鋼を、鋳型内を電磁攪拌しつつ引抜速度２．４ｍ／ｍｉｎで鋳造した結果、鋳型銅チューブ温度の変動が、比較例Ｉを用いた鋳型においては３０℃以上あり操業に支障をきたしたのに対し、実施例Ｂを用いた鋳型においては１０℃以下に抑制され、安定した鋳造が可能であった。鋳型銅チューブ温度はメニスカス下１５０ｍｍ、鋳型表面から５ｍｍの点において測定した。 As a result, the powder entrapment defect occurrence rate was confirmed to be reduced to 1/6 in the case where Example B was used for the pipe manufactured from the slab using Comparative Example N. Also, using Example B and Comparative Example I, 0.2% by mass C-0.6% by mass Mn aluminum deoxidized ordinary steel was cast in a round billet continuous casting with a mold diameter of φ225 mm, and the inside of the mold was electromagnetically stirred. However, as a result of casting at a drawing speed of 2.4 m / min, the variation of the mold copper tube temperature was 30 ° C. or more in the mold using Comparative Example I, which hindered operation, but Example B was used. The mold was suppressed to 10 ° C. or lower, and stable casting was possible. The mold copper tube temperature was measured at a point 150 mm below the meniscus and 5 mm from the mold surface.
あるいは、実施例Ｆと比較例Ｍとを用い、鋳型断面が２３０ｍｍ厚×１２５０ｍｍ幅のスラブ連続鋳造機において、低炭素アルミ脱酸普通鋼を引抜速度１．４ｍ／ｍｉｎで鋳造し、鋳造したスラブの表層から１０ｍｍの範囲におけるパウダー性介在物の量を比較した結果、比較例Ｍを用いたスラブに比べ実施例Ｆを用いたスラブでは、介在物が１／５に減少していることが確認された。 Alternatively, using Example F and Comparative Example M, in a slab continuous casting machine having a mold cross section of 230 mm thickness x 1250 mm width, low carbon aluminum deoxidized ordinary steel was cast at a drawing speed of 1.4 m / min, and the slab was cast. As a result of comparing the amount of powdery inclusions in the range of 10 mm from the surface layer of the slab, it was confirmed that the inclusions were reduced to 1/5 in the slab using Example F compared to the slab using Comparative Example M It was done.
また、実施例Ｅと比較例Ｊを用いて鋳型断面が２３０ｍｍ厚×１１５０ｍｍ幅のスラブ連続鋳造機において、低炭素アルミ脱酸普通鋼を引抜速度１．６ｍ／ｍｉｎで鋳造した結果、鋳型銅板温度の変動が、比較例Ｊを用いた鋳型においては１５℃以上あり、ブレークアウト予知システムの誤作動を引き起こしたのに対し、実施例Ｅを用いた鋳型においては５℃以下に抑制され、安定した鋳造が可能であった。鋳型銅チューブ温度はメニスカス下１００ｍｍ、鋳型表面から１５ｍｍの点において測定した。 Moreover, as a result of casting low carbon aluminum deoxidized ordinary steel at a drawing speed of 1.6 m / min in a slab continuous casting machine having a mold cross section of 230 mm thickness × 1150 mm width using Example E and Comparative Example J, the mold copper plate temperature The fluctuation in the mold using Comparative Example J was 15 ° C. or higher and caused the malfunction of the breakout prediction system, whereas the mold using Example E was suppressed to 5 ° C. or lower and stabilized. Casting was possible. The mold copper tube temperature was measured at a point 100 mm below the meniscus and 15 mm from the mold surface.
以上のように、本発明に係るモールドパウダーは、ビレットやスラブを連続鋳造する際に使用するモールドパウダーとして有用であり、特に清浄な鋼を連続鋳造するためのパウダーとして適している。 As described above, the mold powder according to the present invention is useful as a mold powder used when continuously casting billets and slabs, and is particularly suitable as a powder for continuously casting clean steel.
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