JP4992459B2 - Mold flux for continuous casting of steel and continuous casting method using the mold flux - Google Patents
Mold flux for continuous casting of steel and continuous casting method using the mold flux Download PDFInfo
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- 230000004907 flux Effects 0.000 title claims description 107
- 229910000831 Steel Inorganic materials 0.000 title claims description 44
- 239000010959 steel Substances 0.000 title claims description 44
- 238000009749 continuous casting Methods 0.000 title claims description 15
- 238000000034 method Methods 0.000 title claims description 9
- 238000009736 wetting Methods 0.000 claims description 58
- 238000002425 crystallisation Methods 0.000 claims description 38
- 230000008025 crystallization Effects 0.000 claims description 38
- 239000000758 substrate Substances 0.000 claims description 6
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 5
- 229910052802 copper Inorganic materials 0.000 claims description 5
- 239000010949 copper Substances 0.000 claims description 5
- 239000000843 powder Substances 0.000 claims description 4
- 230000006835 compression Effects 0.000 claims description 3
- 238000007906 compression Methods 0.000 claims description 3
- 238000010438 heat treatment Methods 0.000 claims description 3
- 230000000630 rising effect Effects 0.000 claims description 3
- 239000000155 melt Substances 0.000 claims 1
- 238000007711 solidification Methods 0.000 description 33
- 230000008023 solidification Effects 0.000 description 33
- 239000000463 material Substances 0.000 description 13
- 238000005266 casting Methods 0.000 description 9
- 238000005259 measurement Methods 0.000 description 8
- 230000007423 decrease Effects 0.000 description 6
- 238000001816 cooling Methods 0.000 description 5
- 238000002844 melting Methods 0.000 description 5
- 230000008018 melting Effects 0.000 description 5
- 230000000704 physical effect Effects 0.000 description 5
- 229910001209 Low-carbon steel Inorganic materials 0.000 description 4
- 239000011248 coating agent Substances 0.000 description 4
- 229910002441 CoNi Inorganic materials 0.000 description 3
- 238000000576 coating method Methods 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 229910000954 Medium-carbon steel Inorganic materials 0.000 description 2
- 238000005336 cracking Methods 0.000 description 2
- 230000003111 delayed effect Effects 0.000 description 2
- 239000012528 membrane Substances 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 229910052759 nickel Inorganic materials 0.000 description 2
- 238000007747 plating Methods 0.000 description 2
- 239000007790 solid phase Substances 0.000 description 2
- 229910002555 FeNi Inorganic materials 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 238000005452 bending Methods 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 229910052804 chromium Inorganic materials 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000004927 fusion Effects 0.000 description 1
- 238000000265 homogenisation Methods 0.000 description 1
- 238000009413 insulation Methods 0.000 description 1
- 238000005461 lubrication Methods 0.000 description 1
- 230000005499 meniscus Effects 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 230000002265 prevention Effects 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 230000006641 stabilisation Effects 0.000 description 1
- 238000011105 stabilization Methods 0.000 description 1
- 238000004017 vitrification Methods 0.000 description 1
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
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- Treatment Of Steel In Its Molten State (AREA)
Description
本発明は、鋼の連続鋳造用モールドフラックス及び該モールドフラックスを使用した連続鋳造方法に関する。 The present invention relates to a mold flux for continuous casting of steel and a continuous casting method using the mold flux.
図5は鋼の縦型連続鋳造機の鋳型内の一部断面の説明図であり、鋳型内の溶鋼にモールドフラックス(湯面(表面)被覆剤又はモールドパウダとも称する)を添加した状態を示している。溶鋼1の上方には溶融フラックス3、そのさらに上方には未溶融フラックス5がある。そして、鋳型7との境界面には、鋳型7に近い方から順に、固相フラックス膜9、溶融フラックス膜11があり、そのさらに内側には凝固シェル13が形成されている。
FIG. 5 is an explanatory view of a partial cross section in a mold of a vertical continuous casting machine for steel, showing a state in which mold flux (also referred to as a molten metal (surface) coating agent or mold powder) is added to molten steel in the mold. ing. Above the molten steel 1 is a molten flux 3 and further above that is an unmelted flux 5. And in the boundary surface with the casting_mold |
モールドフラックスは、主として、(1)鋳型内の溶鋼表面の被覆保温及び酸化防止、(2)溶鋼中より浮上する非金属介在物の吸収及び溶鋼の清浄化、(3)鋳型と初期凝固シェル間の潤滑性保持、(4)凝固シェル抜熱のコントロールと均一化の目的で、添加される。 Mold flux mainly consists of (1) heat insulation and oxidation prevention on the surface of the molten steel in the mold, (2) absorption of non-metallic inclusions floating in the molten steel and cleaning of the molten steel, and (3) between the mold and the initial solidified shell. (4) It is added for the purpose of controlling the heat removal from the solidified shell and making it uniform.
近年では、生産性の向上のため、鋳造速度がより高速化傾向にあり、このため、溶鋼の鋳型内滞留時間が短くなるので、鋳型出口での鋼の凝固シェル厚みも薄肉化傾向にある。そのため、モールドフラックスによる凝固シェル抜熱のコントロールによって鋳型内凝固を促進することが求められる。
しかしながら、従来、鋳型内での潤滑の安定化技術に関する方法の提案は多いが、鋳型内凝固を促進する方法は、モールドフラックスの凝固温度の低下や、溶融モールドフラックスの凝固後にガラス化傾向する成分系にする方法程度で、その方法は少なかった(特許文献1参照)。
However, there have been many proposals for methods related to stabilization of lubrication in the mold, but methods for promoting in-mold solidification include components that tend to vitrify after the solidification temperature of the mold flux decreases or the solidification of the molten mold flux. There were few methods (refer to patent document 1).
従来例においては、鋼の凝固に与えるモールドフラックスの影響として、フラックスの結晶化温度、ガラス化度(結晶化度合い)、結晶の種類等、複数の要因を考慮する必要がある。このように複数の要因を考慮するという方法では、必ずしも、実機で予想通りの結果が得られるとは限らない。そのため、高速鋳造時において結晶化温度を低く設計して、抜熱能力を強化したフラックス設計にした場合であっても、実際に使用すると鋳型抜熱量が増加せず、鋳型内凝固を十分に促進することができない場合もあった。
また、逆に抜熱量が予想以上に高すぎて、凝固の不均一を却って助長してしまうという問題もあった。
In the conventional example, as the influence of the mold flux on the solidification of the steel, it is necessary to consider a plurality of factors such as the crystallization temperature of the flux, the vitrification degree (crystallization degree), and the type of crystal. As described above, the method of considering a plurality of factors does not always provide the expected result with an actual machine. For this reason, even when the flux design is designed with a low crystallization temperature during high speed casting to enhance the heat removal capability, the amount of heat removal from the mold does not increase when actually used, and solidification within the mold is sufficiently accelerated. In some cases, it was not possible.
On the other hand, there is also a problem that the amount of heat removal is excessively higher than expected, which promotes nonuniform solidification.
本発明は、前記従来の問題点を解消するべくなされたもので、鋳型内での凝固を安定に促進して、高速鋳造を安定化することができる鋼の連続鋳造用モールドフラックスを提供することを目的とする。 The present invention has been made to solve the above-described conventional problems, and provides a mold flux for continuous casting of steel that can stably promote solidification in a mold and stabilize high-speed casting. With the goal.
発明者らは、溶融したモールドフラックスの鋳型表面材に対する濡れ角θ(以下、単に「濡れ角θ」、「モールドフラックスの濡れ角θ」という場合あり)と、モールドフラックスを介した鋼の凝固特性の関係を鋭意研究し、その結果、鋼の鋳型内凝固速度が、フラックスの結晶化温度Tcs以外に濡れ角θにも大きく影響されることを見出した。
そして、発明者等は、上記の知見を前提として、極低炭素鋼スラブを高速にて鋳造し、モールドフラックスの濡れ角θと結晶化温度Tcsの関係におけるブレークアウト(BO)発生の関係を鋭意調査し、濡れ角θと結晶化温度Tcsの関係においてブレークアウト(BO)発生の有無が明確に整理できることを見出し、鋼の初期凝固が速く、且つ、均一・安定化するモールドフラックスの物性条件を発見して、本発明に至った。
The inventors have determined that the wetting angle θ of the molten mold flux with respect to the mold surface material (hereinafter sometimes simply referred to as “wetting angle θ” or “wetting angle θ of the mold flux”) and the solidification characteristics of the steel via the mold flux. As a result, it was found that the solidification rate of steel in the mold is greatly influenced by the wetting angle θ in addition to the crystallization temperature Tcs of the flux.
Based on the above knowledge, the inventors have cast an ultra-low carbon steel slab at high speed, and are keenly aware of the relationship between the occurrence of breakout (BO) in the relationship between the mold flux wetting angle θ and the crystallization temperature Tcs. Investigated and found that the presence or absence of breakout (BO) can be clearly arranged in the relationship between the wetting angle θ and the crystallization temperature Tcs, and the physical properties of the mold flux to make the initial solidification of steel fast and uniform and stable. It discovered and came to this invention.
(1)本発明に係る鋼の連続鋳造用モールドフラックスは、溶融フラックスの濡れ角θ(°)が、フラックスの結晶化温度Tcs(℃)の関数として、次式で与えられることを特徴とするものである。
0.12(Tcs−800)≦θ≦70
(1) The mold flux for continuous casting of steel according to the present invention is characterized in that the wetting angle θ (°) of the molten flux is given by the following equation as a function of the crystallization temperature Tcs (° C.) of the flux. Is.
0.12 (Tcs−800) ≦ θ ≦ 70
ここで濡れ角θとは、1430℃で60分保持した溶融フラックスを、銅板上に凝固させ、100メッシュアンダー粉末とした0.5gを、10φ×3mmのタブレット状に圧縮力1トンで圧縮整形したものを、図1に示す如く、Co85%Ni15%めっきしたSUS304基板上にセットし、横型管状炉内でArガスを導入しながら昇温速度5〜10℃/分で加熱途中の1140℃における溶融フラックスをビデオ撮影し、その接触角θとして定義される。 Here, the wetting angle θ means that the molten flux held at 1430 ° C. for 60 minutes is solidified on a copper plate and 0.5 g made into 100 mesh under powder is compressed into a 10φ × 3 mm tablet with a compression force of 1 ton. As shown in FIG. 1, it is set on a SUS304 substrate plated with Co85% Ni15%, and heated at 1140 ° C. during heating at a temperature rising rate of 5-10 ° C./min while introducing Ar gas in a horizontal tubular furnace. The molten flux is filmed and defined as its contact angle θ.
(2)本発明に係る連続鋳造方法は、上記(1)に記載した連続鋳造用モールドフラックスを用いることを特徴とするものである。 (2) The continuous casting method according to the present invention is characterized by using the mold flux for continuous casting described in (1) above.
本発明によれば、鋳片冷却の均一化を図れると共に、鋳型内での凝固を安定的に促進して、高速の連続鋳造を安定化することができる。 According to the present invention, slab cooling can be made uniform and solidification in the mold can be stably promoted to stabilize high-speed continuous casting.
前述のように、発明者らは、溶融したモールドフラックスの鋳型表面材に対する濡れ角θと、モールドフラックスを介した鋼の凝固特性の関係を鋭意研究し、その結果、鋼の鋳型内凝固速度が、モールドフラックスの濡れ角θとモールドフラックスの結晶化温度Tfcsに大きく影響されることを発見した。 As described above, the inventors diligently studied the relationship between the wetting angle θ of the molten mold flux with respect to the mold surface material and the solidification characteristics of the steel through the mold flux. It was discovered that the mold flux was greatly affected by the wetting angle θ of the mold flux and the crystallization temperature Tfcs of the mold flux.
図2は、濡れ角θと鋼の凝固特性の関係を模式的に示すグラフであり、横軸が濡れ角θを示し、縦軸が上段から順に、伝熱抵抗(上段)、シェル不均一度(中段)、シェル厚(下段)を示している。
以下においては、図2を参照しながら、溶融したモールドフラックスの鋳型表面材に対する濡れ角θと、モールドフラックスを介した鋼の凝固特性について説明する。
なお、図2中に示した、Rは凝固シェル・鋳型間での総括熱抵抗、λfはフラックスの熱伝導率、Rintはフラックスと鋳型間の界面熱抵抗、dfはフラックス全厚みである。
FIG. 2 is a graph schematically showing the relationship between the wetting angle θ and the solidification characteristics of steel. The horizontal axis indicates the wetting angle θ, and the vertical axis indicates the heat transfer resistance (upper stage) and the shell nonuniformity in order from the upper stage. (Middle stage) and shell thickness (lower stage) are shown.
Hereinafter, the wetting angle θ of the melted mold flux with respect to the mold surface material and the solidification characteristics of the steel through the mold flux will be described with reference to FIG.
2, R is the overall thermal resistance between the solidified shell and the mold, λf is the thermal conductivity of the flux, Rint is the interface thermal resistance between the flux and the mold, and df is the total thickness of the flux.
溶融したモールドフラックスが鋳型に対して濡れやすい(濡れ角が小さい)場合、溶融したモールドフラックスと鋳型との接触面積が増大(界面熱抵抗Rintが減少)し、接触直後の鋳型への伝熱が促進される。このため、溶融したモールドフラックスの凝固が速く進行し、鋳型〜凝固シェル間のフラックス厚みdfが厚く成長する結果、伝熱抵抗が増大する(上段の図参照)。
よって、その後に凝固する溶鋼は、一層均一に凝固シェルが成長しやすくなる(中段の図参照)。
しかしながら、伝熱抵抗が大きいために、シェル成長速度が抑制されシェル厚は厚くならない(下段の図参照)。
一方、濡れが良すぎ、かつフラックス結晶化温度Tcsが小さいフラックスの場合も同様の結果となる。この場合も、界面熱抵抗Rintが小さいもののフラックス厚みdfは増加しづらい。このため、一層伝熱抵抗が小さくなり、凝固する鋼の冷却速度が増大する結果、凝固シェルは不均一に成長し易くなり、シェル厚は厚く成長しない。
When the melted mold flux is easily wetted with the mold (the wetting angle is small), the contact area between the melted mold flux and the mold is increased (interfacial thermal resistance Rint is decreased), and the heat transfer to the mold immediately after contact is increased. Promoted. For this reason, solidification of the melted mold flux proceeds rapidly, and the flux thickness df between the mold and the solidified shell grows thick. As a result, the heat transfer resistance increases (see the upper diagram).
Therefore, in the molten steel that solidifies thereafter, the solidified shell is more likely to grow more uniformly (see the middle figure).
However, since the heat transfer resistance is large, the shell growth rate is suppressed and the shell thickness does not increase (see the lower figure).
On the other hand, the same result is obtained when the flux is too wet and the flux crystallization temperature Tcs is low. Also in this case, although the interfacial thermal resistance Rint is small, the flux thickness df is difficult to increase. For this reason, the heat transfer resistance is further reduced and the cooling rate of the solidified steel is increased. As a result, the solidified shell tends to grow unevenly, and the shell thickness does not grow thick.
このような場合において、フラックス結晶化温度Tcsが高いと、伝熱抵抗がより増大して均一化効果が促進されるが、一方で凝固する鋼のシェル成長速度が抑制され過ぎてブレークアウト(BO)の危険が増す。
よって、例えば中炭素鋼など表面割れの発生し易い鋼の高速鋳造時に、割れ防止のため敢えて結晶化温度Tcsの高いフラックスを使用する場合は、このようなシェル肉薄現象を抑制するため、濡れ角の大きなフラックスを使用してフラックスの凝固を抑制する必要がある。つまり、ブレークアウト(BO)を防止する最小の濡れ角は結晶化温度Tcsの増加につれて大きくなる。
In such a case, if the flux crystallization temperature Tcs is high, the heat transfer resistance is further increased and the homogenization effect is promoted. On the other hand, the shell growth rate of the solidified steel is excessively suppressed and breakout (BO ) Is increased.
Therefore, for example, when using a flux with a high crystallization temperature Tcs to prevent cracking during high-speed casting of steel that is prone to surface cracking, such as medium carbon steel, the wetting angle is used to suppress such a shell thinning phenomenon. It is necessary to suppress the solidification of the flux using a large flux. That is, the minimum wetting angle for preventing breakout (BO) increases as the crystallization temperature Tcs increases.
一方、濡れが悪い(濡れ角が大きい)場合、濡れが良い場合とは逆の現象が起こる。つまり、溶融フラックスと鋳型との接触面積が減少(界面熱抵抗Rintが増加)するため、接触直後の鋳型への伝熱は適度に抑制され、溶融フラックスの凝固も遅くなる。このため、鋳型〜凝固シェル間の全フラックス厚みdfは、濡れが良い場合と比較して薄くなる。その結果、全体(凝固シェル〜鋳型間)の総括伝熱抵抗が低下する(上段の図参照)。
総括伝熱抵抗が低下することにより、鋼の凝固が促進され、シェル厚は厚くなる(下段の図参照)。
濡れが少し悪くなってもシェル不均一度への影響は少ないが、濡れが更に悪くなると、鋳型へのフラックスの接触状態の不均一化も手伝って、鋼の凝固の不均一性が助長され、シェル厚が薄くなる(中段の図参照)。その結果、ブレークアウト(BO)が発生し易くなる。
よって、鋼の凝固の均一性を確保するためには濡れ角に上限が存在することとなる。
本発明において、濡れ角の最適値に上限70°があるのは、このような理由からである。
On the other hand, when wetting is poor (wetting angle is large), the opposite phenomenon occurs when wetting is good. That is, since the contact area between the molten flux and the mold decreases (interfacial thermal resistance Rint increases), heat transfer to the mold immediately after contact is moderately suppressed, and solidification of the molten flux is also delayed. For this reason, the total flux thickness df between the mold and the solidified shell is reduced compared to the case where wetting is good. As a result, the overall heat transfer resistance of the whole (between the solidified shell and the mold) decreases (see the upper diagram).
By reducing the overall heat transfer resistance, solidification of the steel is promoted and the shell thickness is increased (see the lower figure).
Even if wetting is a little worse, there is little impact on the non-uniformity of the shell, but when wetting gets worse, the non-uniformity of the solidification of the steel is promoted, helping the non-uniformity of the contact state of the flux to the mold, The shell thickness is reduced (see the middle figure). As a result, breakout (BO) is likely to occur.
Therefore, there is an upper limit on the wetting angle in order to ensure the solidification uniformity of the steel.
In the present invention, the optimum value of the wetting angle has an upper limit of 70 ° for this reason.
なお、抜熱量:H、鋼の凝固シェル表面温度:Ts、鋳型表面温度:Tc、凝固シェル・鋳型間での総括熱抵抗:R、フラックスの熱伝導率:λf、フラックスと鋳型間の界面熱抵抗:Rint、フラックス全厚み:dfの関係を簡略化した数式で表現すると次式に示す如くなる。
H=(Ts−Tc)/R=(Ts―Tc)/(Rint+df/λf)
The amount of heat removal: H, the solidified shell surface temperature of steel: Ts, the mold surface temperature: Tc, the overall thermal resistance between the solidified shell and the mold: R, the thermal conductivity of the flux: λf, the interfacial heat between the flux and the mold When the relationship between the resistance: Rint and the total flux thickness: df is expressed by a simplified formula, the following formula is obtained.
H = (Ts−Tc) / R = (Ts−Tc) / (Rint + df / λf)
以上のように、フラックスの結晶化温度Tcs以外に濡れ角θが、鋼の凝固に大きく影響されることを見出した。 As described above, it has been found that the wetting angle θ is greatly influenced by the solidification of the steel other than the crystallization temperature Tcs of the flux.
発明者等は、上記の知見を前提に、垂直曲げ型の鋼の連鋳機において、極低炭素鋼(ULC)(C:0.0010〜0.0030,Si<0.20,Mn:0.1〜0.5,P:0.005〜0.030,S:0.0001〜0.015,Al:0.01〜0.04質量%)スラブ(サイズ220〜235mm×1000〜1800mm)を、鋳造速度2.0〜2.6m/分で鋳造し、ブレークアウト発生率を調査した。
表1は、使用したモールドフラックス別のブレークアウト(BO)発生率(1チャージ当りのBO発生数)をまとめて示したものである。
Based on the above knowledge, the inventors of the present invention used an ultra-low carbon steel (ULC) (C: 0.0010 to 0.0030, Si <0.20, Mn = 0) in a vertical bending type steel continuous casting machine. 0.1 to 0.5, P: 0.005 to 0.030, S: 0.0001 to 0.015, Al: 0.01 to 0.04% by mass) Slab (size 220 to 235 mm × 1000 to 1800 mm) Was cast at a casting speed of 2.0 to 2.6 m / min, and the occurrence rate of breakout was investigated.
Table 1 summarizes the breakout (BO) generation rate (number of BO generation per charge) for each mold flux used.
また、表1の結果を、濡れ角θ(°)と結晶化温度Tcs(℃)の関係におけるブレークアウト(BO)発生の有無を示すグラフで示したものが図3である。図3においては、縦軸が濡れ角θ(°)を示し、横軸が結晶化温度Tcs(℃)を示している。また、図3において、白丸がブレークアウト(BO)の発生がない場合を示し、黒丸がブレークアウト(BO)の発生が有る場合を示している。 Further, FIG. 3 shows the result of Table 1 as a graph showing the occurrence of breakout (BO) in the relationship between the wetting angle θ (°) and the crystallization temperature Tcs (° C.). In FIG. 3, the vertical axis indicates the wetting angle θ (°), and the horizontal axis indicates the crystallization temperature Tcs (° C.). In FIG. 3, a white circle indicates a case where no breakout (BO) occurs, and a black circle indicates a case where a breakout (BO) occurs.
図3に示すグラフから、モールドフラックスの濡れ角θと結晶化温度Tcsの関係においてブレークアウト(BO)発生の有無が明確に整理できることがわかる。
そして、ブレークアウト(BO)発生を防止するためには、図3における白丸の領域になるように、モールドフラックスの濡れ角θ(°)と結晶化温度Tcs(℃)の関係を設定すればよい。
すなわち、鋼の初期凝固が速く、且つ、均一・安定化してブレークアウト(BO)の発生を防止できるモールドフラックスの物性条件として、モールドフラックスの濡れ角θ(°)と結晶化温度Tcs(℃)の関係が、図3における破線で囲まれる範囲になるように設定すればよい。この関係を数式で示すと、以下の(1)式になる。
0.12(Tcs−800)≦θ≦70 ・・・・・ (1)
From the graph shown in FIG. 3, it can be seen that the presence or absence of breakout (BO) can be clearly arranged in the relationship between the wetting angle θ of the mold flux and the crystallization temperature Tcs.
In order to prevent the occurrence of breakout (BO), the relationship between the mold flux wetting angle θ (°) and the crystallization temperature Tcs (° C.) may be set so as to be the white circle region in FIG. .
That is, the mold flux wetting angle θ (°) and the crystallization temperature Tcs (° C.) are the physical properties of the mold flux that can quickly solidify and stabilize the steel to prevent the occurrence of breakout (BO). May be set so as to be in a range surrounded by a broken line in FIG. This relationship is expressed by the following equation (1).
0.12 (Tcs−800) ≦ θ ≦ 70 (1)
図4は、図3のグラフにおける領域をA〜Fの6つの領域に分けて示し、各領域に相当する物性条件を有するモールドフラックスを使用した場合における鋳造時のモールドフラックス及び凝固シェルの状態を模式的に示した図である。以下においては、図4に基づいて、図4の各領域におけるモールドフラックス及び凝固シェルの状態について説明する。
なお、上述の説明からも分かるように、モールドフラックスの結晶化温度Tcsが高くなると、溶鋼の凝固速度が小さくなり、逆にモールドフラックスの結晶化温度Tcsが低くなると、溶鋼の凝固速度が大きくなる。
また、濡れ角θが大きくなる(濡れ性が悪くなる)と、不均一凝固の傾向になると共に冷却抑制の傾向になる。逆に、濡れ角θが小さくなる(濡れ性が良くなる)と、均一凝固の傾向になると共に冷却促進の傾向になる。
FIG. 4 shows the region in the graph of FIG. 3 divided into six regions A to F, and shows the state of the mold flux and the solidified shell at the time of casting when a mold flux having physical property conditions corresponding to each region is used. It is the figure shown typically. Below, based on FIG. 4, the state of the mold flux and the solidified shell in each area | region of FIG. 4 is demonstrated.
As can be seen from the above description, when the mold flux crystallization temperature Tcs increases, the solidification rate of the molten steel decreases. Conversely, when the mold flux crystallization temperature Tcs decreases, the solidification rate of the molten steel increases. .
Further, when the wetting angle θ is increased (wetting property is deteriorated), the tendency to non-uniform solidification and the tendency to suppress cooling. On the other hand, when the wetting angle θ is small (wetting property is improved), the tendency to uniform solidification and the tendency to promote cooling are obtained.
(1)A領域
A領域の物性条件は、結晶化温度Tcsが高く、濡れ角θが小さいものである。この領域では、結晶化温度Tcsが高いことからモールドフラックスの凝固が早期に起こり、フラックス厚みdfが厚くなる。また、濡れ角θが小さいことから、フラックス、鋼ともに均一凝固の傾向が強い。
しかし、フラックス厚みdfが厚いので、溶鋼の凝固の進行が遅く凝固シェル厚みdsが薄く、ブレークアウト(BO)発生の危険がある。
(1) Region A The physical properties of the region A are that the crystallization temperature Tcs is high and the wetting angle θ is small. In this region, since the crystallization temperature Tcs is high, the mold flux is quickly solidified, and the flux thickness df is increased. Moreover, since the wetting angle θ is small, the tendency of uniform solidification is strong for both flux and steel.
However, since the flux thickness df is large, the solidification of the molten steel is slow and the solidified shell thickness ds is thin, which may cause a breakout (BO).
(2)B領域
B領域は、A領域と結晶化温度Tcsは同じであるが、濡れ角θを大きくしたものである。濡れ角θを大きくしたことにより、接触直後における鋳型への伝熱が抑制され、溶融フラックスの凝固が遅くなるため、フラックス厚みdfが薄くなり、伝熱抵抗は減少する。そのため、溶鋼は不均一凝固の傾向にはなるが、凝固シェル厚みdsがA領域の場合よりも大きくなり、ブレークアウト(BO)発生が回避される。
(2) B region The B region has the same crystallization temperature Tcs as the A region, but has a larger wetting angle θ. By increasing the wetting angle θ, heat transfer to the mold immediately after contact is suppressed, and solidification of the molten flux is delayed, so that the flux thickness df is reduced and the heat transfer resistance is reduced. Therefore, the molten steel tends to be non-uniformly solidified, but the solidified shell thickness ds becomes larger than that in the region A, and breakout (BO) is avoided.
(3)C領域
C領域は、A、B領域と結晶化温度Tcsは同じであるが、濡れ角θをB領域よりもさらに大きくしたものである。濡れ角θをさらに大きくしたことにより、鋳型へのフラックスの接触状態がさらに不均一になり、フラックスと鋳型間での熱抵抗(界面熱抵抗Rint)が大きくなる。その結果、フラックス厚みdfがB領域の場合よりも薄くなるが、総括伝熱抵抗Rは増大することになる。よって、凝固シェル厚みdsは薄く、かつ、不均一となり、ブレークアウト(BO)発生の危険が発生する。
(3) C region The C region has the same crystallization temperature Tcs as the A and B regions, but the wetting angle θ is larger than that of the B region. By further increasing the wetting angle θ, the contact state of the flux with the mold becomes more uneven, and the thermal resistance between the flux and the mold (interfacial thermal resistance Rint) increases. As a result, the flux thickness df becomes thinner than that in the B region, but the overall heat transfer resistance R increases. Therefore, the solidified shell thickness ds is thin and non-uniform, and a risk of breakout (BO) occurs.
(4)D領域
D領域は、A領域の場合と濡れ角θが同じであるが、結晶化温度Tcsを低くしたものである。結晶化温度Tcsが低く、かつ濡れ角θが小さいので、フラックス厚みdfは均一かつ薄く成長するものの鋼は急冷される。その結果、凝固シェルの熱収縮が増し不均一凝固が助長される。この場合、凝固シェルの平均厚みはA領域の場合よりも大きいが、最小の厚みはA領域の場合と大差なく、ブレークアウト(BO)発生の危険がある。
(4) D region The D region has the same wetting angle θ as in the A region, but has a lower crystallization temperature Tcs. Since the crystallization temperature Tcs is low and the wetting angle θ is small, the steel is rapidly cooled although the flux thickness df grows uniformly and thinly. As a result, the thermal shrinkage of the solidified shell is increased and nonuniform solidification is promoted. In this case, the average thickness of the solidified shell is larger than that in the A region, but the minimum thickness is not much different from that in the A region, and there is a risk of occurrence of breakout (BO).
(5)E領域
E領域は、D領域の場合と結晶化温度Tcsが同じであるが、濡れ角θを大きくしたものである。結晶化温度Tcsが低いためフラックス厚みdfが薄いが、濡れ角θを大きくしたことにより、界面熱抵抗Rintが増し、溶鋼の冷却速度がD領域の場合よりも緩和され、溶鋼の不均一凝固が緩和される。そのため、凝固シェルが均一に厚くなり、ブレークアウト(BO)発生が回避される。
(5) E region The E region has the same crystallization temperature Tcs as in the D region, but has a larger wetting angle θ. Since the crystallization temperature Tcs is low, the flux thickness df is thin, but by increasing the wetting angle θ, the interfacial thermal resistance Rint is increased, the cooling rate of the molten steel is less than in the D region, and the non-uniform solidification of the molten steel is caused. Alleviated. For this reason, the solidified shell is uniformly thickened, and the occurrence of breakout (BO) is avoided.
(6)F領域
F領域は、D、E領域と結晶化温度Tcsは同じであるが、濡れ角θをE領域よりもさらに大きくしたものである。濡れ角θをさらに大きくしたことにより、鋳型へのフラックスの接触状態がさらに不均一になり、フラックスと鋳型間での熱抵抗が大きくなる。その結果、フラックス厚みdfはE領域の場合よりも薄くなるが不均一になるため、凝固シェル厚みdsも薄くなり、また溶鋼の凝固も不均一となり、ブレークアウト(BO)発生の危険が発生する。
(6) F region The F region has the same crystallization temperature Tcs as the D and E regions, but the wetting angle θ is larger than that of the E region. By further increasing the wetting angle θ, the contact state of the flux with the mold becomes more uneven, and the thermal resistance between the flux and the mold increases. As a result, the flux thickness df becomes thinner than that in the E region but becomes non-uniform, so the solidified shell thickness ds also becomes thin, and the solidification of the molten steel becomes non-uniform, which causes a risk of breakout (BO). .
以上のように、A〜F領域のうちのB、E領域ではブレークアウト(BO)発生の危険が回避されることが定性的に説明でき、これは上述した(1)式の関係を満たすモールドフラックスを使用することにより、ブレークアウト(BO)発生を回避できることの理論的な裏づけとなる。 As described above, it can be qualitatively explained that the risk of occurrence of breakout (BO) is avoided in the B and E regions in the A to F regions, which is a mold that satisfies the relationship of the above-described equation (1). The use of flux provides a theoretical support for the ability to avoid the occurrence of breakout (BO).
なお、図1に示すθで定義される濡れ角は、一般に温度依存性がある。よって、本発明では、1140℃で5〜10℃/分における値とした。これは、1140℃以上ではθが小さくなり過ぎ、測定困難になるためである。 Note that the wetting angle defined by θ shown in FIG. 1 generally has temperature dependence. Therefore, in this invention, it was set as the value in 5-10 degree-C / min at 1140 degreeC. This is because at 1140 ° C. or higher, θ becomes too small and measurement becomes difficult.
基板材質としては、一般的に鋳型銅板表面に使用されているコーティング材(Cr、Ni、FeNi、CoNiなど)が理想であるが、前述した高温でのフラックスの反応が殆ど無いCoNiメッキが最適である。 The substrate material is ideally a coating material (Cr, Ni, FeNi, CoNi, etc.) that is generally used on the surface of the mold copper plate, but CoNi plating that has almost no flux reaction at the above-mentioned temperature is optimal. is there.
濡れ角測定用のフラックスとしては、実際の現象を考慮し、一旦溶融したフラックスを凝固させたものを使用することで、測定ばらつきを抑制できる。又、一般的に一旦溶融させたものを再度溶融(2度溶融)させると、結晶化温度Tcsが低下する現象があるため、1度目の溶融後に測定されるフラックスの結晶化温度Tcs(粘度が急上昇する温度)よりも低温側から溶融する。よって、一度目の溶融後に測定する結晶化温度Tcsよりも低い1140℃でも接触角が測定できる。本発明で定義する結晶化温度Tcsは、2回目の溶融後に測定される結晶化温度Tcsであり、一般的に温度降下時(5〜10℃/分)の粘度が急激に上昇する温度を指す。
本発明では、回転粘度計で温度降下速度5℃/minで連続測定し、粘度が急激に上昇する温度を結晶化温度Tcsとした。
As the wetting angle measurement flux, in consideration of the actual phenomenon, measurement flux can be suppressed by using a solidified flux once melted. In general, once the melted material is melted again (melted twice), there is a phenomenon that the crystallization temperature Tcs is lowered. Therefore, the flux crystallization temperature Tcs (viscosity is measured after the first melting). Melting from the lower temperature side than the rapidly rising temperature). Therefore, the contact angle can be measured even at 1140 ° C. lower than the crystallization temperature Tcs measured after the first melting. The crystallization temperature Tcs defined in the present invention is the crystallization temperature Tcs measured after the second melting, and generally refers to the temperature at which the viscosity rapidly rises when the temperature drops (5 to 10 ° C./min). .
In the present invention, continuous measurement was performed at a temperature drop rate of 5 ° C./min with a rotary viscometer, and the temperature at which the viscosity increased rapidly was defined as the crystallization temperature Tcs.
よって、本発明の濡れ角θは、1430℃で60分保持した溶融モールドフラックスを銅板上に凝固させ、100メッシュアンダー粉末とした0.5gを10φ×3mmのタブレット状に圧縮力1トンで圧縮整形したものを、Co85%Ni15%めっき(厚み0.2mm)したSUS304基板(板厚0.8〜1.0mm冷延板)上にセットし、横型管状炉内でArガス(純度99.999%、流量1Nl/分)を導入しながら昇温速度5〜10℃/分で加熱途中の1140℃における溶融フラックスの形状をビデオ撮影し、その接触角θとして定義した。 Therefore, the wetting angle θ of the present invention is obtained by solidifying the molten mold flux held at 1430 ° C. for 60 minutes on a copper plate and compressing 0.5 g of 100 mesh under powder into a 10φ × 3 mm tablet with a compression force of 1 ton. The shaped product is set on a SUS304 substrate (plate thickness 0.8-1.0 mm cold-rolled plate) plated with Co 85% Ni 15% (thickness 0.2 mm), and Ar gas (purity 99.999) in a horizontal tubular furnace. The shape of the molten flux at 1140 ° C. during heating was introduced at a rate of temperature increase of 5-10 ° C./min while introducing a flow rate of 1 Nl / min) and defined as the contact angle θ.
測定温度1140℃は1つの基準であるが、この値である必要性は特になく、フラックスの結晶化温度Tcsが高くなりすぎたり、逆に極端に低くなりすぎたりした場合には、測定不能になるので、これを避けるため、基準温度(1140℃)を上下させて、測定が可能な温度に設定すればよい。その場合は、最適な濡れ角も測定温度の高低に影響されて減増することはいうまでもない。 The measurement temperature of 1140 ° C. is one standard, but this value is not particularly necessary. If the crystallization temperature Tcs of the flux becomes too high or extremely low, the measurement becomes impossible. Therefore, in order to avoid this, the reference temperature (1140 ° C.) may be raised and lowered to a temperature at which measurement is possible. In that case, needless to say, the optimum wetting angle also decreases depending on the measurement temperature.
濡れ角θは、基板材質にも影響されるが、実際に実機で使用中の鋳型表面温度は250〜400℃と低温であるため、鋳型表面材が金属や合金の場合、鋳型表面材の濡れ角への影響は無視できる。よって、CoNiめっきを基板として使用して測定した濡れ角を基準としても、ブレークアウト(BO)に及ぼす濡れ角の影響の程度が、実際に使用する鋳型表面材の影響を受けることは無視できる。 Although the wetting angle θ is affected by the substrate material, the mold surface temperature during actual use in an actual machine is as low as 250 to 400 ° C. Therefore, when the mold surface material is a metal or alloy, the mold surface material is wet. The effect on the corner is negligible. Therefore, even if the wetting angle measured using CoNi plating as a substrate is used as a reference, it can be ignored that the degree of the effect of the wetting angle on the breakout (BO) is influenced by the mold surface material actually used.
又、鋳型メニスカス部の表面のコーティング材の厚みは、0.2μm〜0.5mmと薄いため、鋳型銅板全厚(20〜50mm)に占める割合が小さく、それ自体の熱抵抗は無視し得る。よって、表面材の厚みの違いによって本発明で発見した最適な濡れ角が変化することはない。 Moreover, since the thickness of the coating material on the surface of the mold meniscus portion is as thin as 0.2 μm to 0.5 mm, the ratio of the coating material to the total thickness of the mold copper plate (20 to 50 mm) is small, and its own thermal resistance can be ignored. Therefore, the optimum wetting angle discovered in the present invention does not change due to the difference in the thickness of the surface material.
なお、本発明のモールドフラックスは不均一凝固しやすい鋼の高速鋳造時のBO発生防止に好適であり、一般的な極低炭素鋼や中炭素鋼の鋳造に適用できる。
なお、一般的な極低炭素鋼の成分組成範囲を以下に示す。
C:0.0010〜0.0030,Si<0.20,Mn:0.1〜0.5,P:0.005〜0.030,S:0.0001〜0.015,Al:0.01〜0.04質量%
The mold flux of the present invention is suitable for preventing the occurrence of BO during high-speed casting of steel that tends to solidify unevenly, and can be applied to casting of general ultra-low carbon steel and medium carbon steel.
In addition, the component composition range of a general very low carbon steel is shown below.
C: 0.0010 to 0.0030, Si <0.20, Mn: 0.1 to 0.5, P: 0.005 to 0.030, S: 0.0001 to 0.015, Al: 0. 01-0.04 mass%
1 溶鋼
3 溶融フラックス
5 未溶融フラックス
7 鋳型
9 固相フラックス膜
11 溶融フラックス膜
13 凝固シェル
DESCRIPTION OF SYMBOLS 1 Molten steel 3 Molten flux 5
Claims (2)
0.12(Tcs−800)≦θ≦70
但し、濡れ角θとは、1430℃で60分保持した溶融フラックスを、銅板上に凝固させ、100メッシュアンダー粉末とした0.5gを、10φ×3mmのタブレット状に圧縮力1トンで圧縮整形したものを、Co85%Ni15%めっきしたSUS304基板上にセットし、横型管状炉内でArガスを導入しながら昇温速度5〜10℃/分で加熱途中の1140℃における溶融フラックスの接触角θとして定義される。 A mold flux for continuous casting of steel, characterized in that the wetting angle θ (°) of the molten flux is given by the following equation as a function of the crystallization temperature Tcs (° C) of the flux.
0.12 (Tcs−800) ≦ θ ≦ 70
However, the wetting angle θ means that the molten flux held at 1430 ° C. for 60 minutes is solidified on a copper plate, and 0.5 g of 100 mesh under powder is compressed into a 10φ × 3 mm tablet with a compression force of 1 ton. This was set on a SUS304 substrate plated with Co85% Ni15%, and the contact angle θ of the melt flux at 1140 ° C. during heating at a temperature rising rate of 5-10 ° C./min while introducing Ar gas in a horizontal tubular furnace. Is defined as
A continuous casting method for steel using the mold flux for continuous casting according to claim 1.
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