JP2007111721A - Heat-retaining material for molten steel surface, and continuous casting method for steel using the same - Google Patents
Heat-retaining material for molten steel surface, and continuous casting method for steel using the same Download PDFInfo
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本発明は、連続鋳造用タンディッシュや取鍋などにより溶鋼を移送、又は精錬処理を行う際に、断熱・保温あるいは空気酸化防止を目的として溶鋼表面を被覆する溶鋼表面保温材およびそれを用いた連続鋳造方法に関するものである。 The present invention uses a molten steel surface heat insulating material that coats the molten steel surface for the purpose of heat insulation / heat retention or air oxidation prevention when the molten steel is transferred or refined by a tundish or ladle for continuous casting, and the like. The present invention relates to a continuous casting method.
連続鋳造用タンディッシュや取鍋などにより溶鋼を移送、又は精錬処理を行う際、保温材を用いて溶鋼表面を被覆し溶鋼からの熱放散と外気の溶鋼への侵入を防止している。従来から保温材として、籾殻を蒸し焼きにした焼籾が主に用いられ、その主成分はSiO2とCである。SiO2は熱伝導率が低く保温効果に、Cは酸素をCOガスに変えるため酸素の遮断効果に優れている。このため、焼籾は保温効果及び空気遮断効果を有し、しかも安価であることを特徴とする保温材である。しかしながら、加工性向上の目的から鋼板中のC濃度を極力低下させた、例えばC濃度が50ppm以下の極低炭素鋼において、保温材中のC成分が溶鋼中にピックアップされ、鋼材の特性を低下させる欠点が知られている。また、保温材中のSiO2成分は溶鋼中のAlと反応してAl2O3系の介在物を生成するため、表面欠陥を増大させるといった問題も生じる。従来、焼籾のこれらの欠点を解決するため、C及びSiO2成分の少ない保温材として、例えば特許文献1に記載されているように、MgO系の保温材が使用されている。また、MgO自体は熱伝導率が高いため、これに断熱性を付与した発泡MgOの製造方法についても種々検討され、特許文献2等に記載されている。 When the molten steel is transferred or refined by a tundish for continuous casting or a ladle, the surface of the molten steel is covered with a heat insulating material to prevent heat dissipation from the molten steel and intrusion of outside air into the molten steel. Conventionally, shochu obtained by steaming rice husk is mainly used as a heat insulating material, and the main components are SiO 2 and C. SiO 2 has a low thermal conductivity and has a heat retention effect, and C has an excellent oxygen blocking effect because it converts oxygen to CO gas. For this reason, shochu is a heat insulating material characterized by having a heat insulating effect and an air blocking effect and being inexpensive. However, for the purpose of improving workability, the C concentration in the steel sheet has been reduced as much as possible, for example, in an extremely low carbon steel having a C concentration of 50 ppm or less, the C component in the heat insulating material is picked up in the molten steel, and the characteristics of the steel material are reduced. There are known drawbacks. Further, since the SiO 2 component in the heat insulating material reacts with Al in the molten steel to generate Al 2 O 3 -based inclusions, there is a problem of increasing surface defects. Conventionally, in order to solve these drawbacks of shochu, an MgO-based heat insulating material is used as a heat insulating material having a small amount of C and SiO 2 components, as described in Patent Document 1, for example. In addition, since MgO itself has a high thermal conductivity, various methods for producing foamed MgO imparted with heat insulation properties have been studied and described in Patent Document 2 and the like.
しかしながら、特許文献1や特許文献2のようなMgOを主成分とする保温材は融点が高く、使用温度では主に粉末或いは焼結状の固相として存在しているため、溶鋼表面の均一な被覆状態が得られず、外気と溶鋼との反応によりAl2O3系介在物を生成する。これに対し、MgOの一部をSiO2、Na2O、或いはCaF2等の低融点化材に置き換えて保温材を溶融させ、溶鋼表面を均一に被覆する方法が考えられるが、この場合SiO2やNa2Oは溶鋼中のAlと反応してAl2O3系介在物を生成し、CaF2はタンディッシュ耐火物を溶損させることにより耐火物起因の介在物を増大させる。 However, since the heat insulating material mainly composed of MgO such as Patent Document 1 and Patent Document 2 has a high melting point and exists mainly as a powder or sintered solid phase at the operating temperature, the surface of the molten steel is uniform. A covering state cannot be obtained, and Al 2 O 3 inclusions are generated by the reaction between the outside air and molten steel. On the other hand, a method in which a part of MgO is replaced with a low melting point material such as SiO 2 , Na 2 O or CaF 2 to melt the heat insulating material and coat the molten steel surface uniformly is considered. 2 and Na 2 O react with Al in the molten steel to produce Al 2 O 3 inclusions, and CaF 2 increases the inclusion due to the refractory by melting the tundish refractory.
これらの問題を鑑み、本発明は空気酸化と保温材の反応に起因する溶鋼汚染を確実に防止できる保温材と、清浄性の優れた鋳片を得るための連続鋳造方法を提供することを目的とするものである。 In view of these problems, an object of the present invention is to provide a heat insulating material that can reliably prevent contamination of molten steel caused by the reaction between air oxidation and the heat insulating material, and a continuous casting method for obtaining a slab excellent in cleanliness. It is what.
上記課題を解決するために、本発明は以下に構成を要旨とする。即ち、
(1)溶鋼表面保温材において、SiO2含有率を5質量%以下、CaO/Al2O3を質量比で1.1〜2.0、MgO含有率を10質量%以上30質量%未満、且つTiを含有したことを特徴とする溶鋼表面保温材。
(2)溶鋼表面保温材において、SiO2含有率を5質量%以下、CaO/Al2O3を質量比で1.1〜2.0、MgO含有率を10質量%以上30質量%未満、且つTiとTiO2を含有したことを特徴とする溶鋼表面保温材。
(3)Tiを0.1〜10質量%含有していることを特徴とする請求項1記載の溶鋼表面保温材。
(4)Tiを0.1〜10質量%、TiO2を2〜30質量%含有していることを特徴とする請求項2記載の溶鋼表面保温材。
(5)鋼の連続鋳造方法において請求項1から4の何れかに記載の溶鋼表面保温材をタンディッシュ内の溶鋼表面上に添加することを特徴とする鋼の連続鋳造方法。
(6)鋼の連続鋳造方法において請求項1から4の何れかに記載の溶鋼表面保温材をタンディッシュ内のTi脱酸溶鋼表面上に添加することを特徴とする鋼の連続鋳造方法。
In order to solve the above problems, the present invention is summarized as follows. That is,
(1) In the molten steel surface heat insulating material, the SiO 2 content is 5% by mass or less, CaO / Al 2 O 3 is 1.1 to 2.0 by mass ratio, and the MgO content is 10% by mass or more and less than 30% by mass, And the molten steel surface heat insulating material characterized by containing Ti.
(2) In the molten steel surface heat insulating material, the SiO 2 content is 5% by mass or less, CaO / Al 2 O 3 is 1.1 to 2.0 by mass ratio, and the MgO content is 10% by mass or more and less than 30% by mass, and the molten steel surface heat insulating material, characterized in that contained Ti and TiO 2.
(3) The molten steel surface heat insulating material according to claim 1, comprising 0.1 to 10% by mass of Ti.
(4) The molten steel surface heat insulating material according to claim 2 , comprising 0.1 to 10% by mass of Ti and 2 to 30% by mass of TiO 2 .
(5) In the continuous casting method of steel, the molten steel surface heat insulating material according to any one of claims 1 to 4 is added onto the molten steel surface in the tundish.
(6) A continuous casting method for steel, wherein the molten steel surface heat insulating material according to any one of claims 1 to 4 is added onto the Ti deoxidized molten steel surface in the tundish.
本発明の溶鋼表面保温材およびこの保温材を用いた連続鋳造方法によれば、溶鋼の汚染は軽減され、鋳造品質は極めて向上する。また、耐火物の溶損もなく、保温材の排滓性も向上するため、操業面でも有効な連続鋳造方法を提供できる。 According to the molten steel surface heat insulating material and the continuous casting method using the heat insulating material of the present invention, contamination of the molten steel is reduced and the casting quality is greatly improved. In addition, since the refractory is not melted and the heat insulating material is improved, the continuous casting method that is effective in terms of operation can be provided.
溶鋼表面を被覆する保温材として満足すべき条件は、溶鋼の保温性を確保した上で、空気酸化と保温材の反応に起因する溶鋼の汚染を確実に防止し、かつ、長時間使用できるようにタンディッシュ耐火物の溶損を防止することである。 Conditions that should be satisfied as a heat insulating material covering the surface of the molten steel are to ensure that the molten steel is kept warm, to reliably prevent contamination of the molten steel due to the reaction between the air oxidation and the heat insulating material, and to be able to be used for a long time. It is to prevent the tundish refractory from melting.
発明者らはこれら基本条件を満足すべく保温材の検討を進めた結果、保温材と溶鋼の反応を防止するためには低SiO2化が、また空気酸化を抑制するためにはCaO/Al2O3の質量比を適正化した上でTiを少量含有させることが、さらに、タンディッシュ耐火物の溶損を防止するためにはMgOを添加することが有効であることを見いだした。 As a result of studying the heat insulating material to satisfy these basic conditions, the inventors have reduced SiO 2 to prevent the reaction between the heat insulating material and molten steel, and CaO / Al to suppress air oxidation. It has been found that it is effective to add a small amount of Ti after optimizing the mass ratio of 2 O 3 , and to add MgO to prevent the tundish refractory from melting.
保温材中のSiO2は[式1]と[式2]により溶鋼中のAlやTiと反応するため、保温材の低SiO2化はAl2O3系介在物やチタニア系介在物の生成防止の効果を有する。
3SiO2+4Al=2Al2O3+3Si [式1]
SiO2+Ti=TiO2+Si [式2]
Since SiO 2 in the heat insulating material reacts with Al and Ti in the molten steel according to [Formula 1] and [Formula 2], reducing the heat insulating material to SiO 2 generates Al 2 O 3 inclusions and titania inclusions. Has the effect of prevention.
3SiO 2 + 4Al = 2Al 2 O 3 + 3Si [Formula 1]
SiO 2 + Ti = TiO 2 + Si [Formula 2]
本発明で規定のCaO−Al2O3−MgO成分系において保温材中のSiO2含有率が5質量%以下になると、[式1]と[式2]の反応速度は急速に低下し、実質的に生成するAl2O3系介在物やチタニア系介在物が減少するため、SiO2含有率を5質量%以下にする必要がある。SiO2を全く含まなければ、[式1]と[式2]の反応は起こらないので、当然その下限値は0質量%を含む。 In the CaO—Al 2 O 3 —MgO component system defined in the present invention, when the SiO 2 content in the heat insulating material is 5% by mass or less, the reaction rates of [Formula 1] and [Formula 2] rapidly decrease, Since Al 2 O 3 -based inclusions and titania-based inclusions that are substantially generated are reduced, the SiO 2 content must be 5% by mass or less. If SiO 2 is not included at all, the reaction of [Formula 1] and [Formula 2] does not occur, so the lower limit value naturally includes 0% by mass.
また、タンディッシュ内溶鋼の空気酸化を防止するためには、保温材を低融点化し、溶鋼表面を保温材で均一に被覆することにより、溶鋼中への空気の侵入を遮断することが重要である。CaO−Al2O3系保温材を低融点化するためには、CaO/Al2O3を0.5〜2.0の範囲にする必要があり、CaO/Al2O3が0.5未満および2.0超の範囲では保温材の溶融温度が鋼の融点1536℃以上となり溶融し難いためである。なお、保温材の溶融温度は、10mm直径×10mm高さの保温材タブレットを加熱炉中で昇温し、保温材タブレットの高さが1/2になった際の温度とする。さらに、CaO−Al2O3系保温材中にTiを添加すると、部分的に保温材が未溶融状態である領域に侵入してきた酸素をTiがTiO2として固定するため、保温材溶融のばらつきまで考慮した上で確実に空気遮断することが可能となる。タンディッシュへの保温材投入は、手投げて実施されることが殆どであり、タンディッシュ内の場所により保温材厚みは均一でなく、溶融状態も一定ではないため、保温材へのTi添加による酸素固定効果は保温材の空気遮断効果を大きく向上させる。 In order to prevent air oxidation of molten steel in the tundish, it is important to lower the melting point of the heat insulating material and to uniformly cover the surface of the molten steel with the heat insulating material, thereby blocking air intrusion into the molten steel. is there. In order to lower the melting point of the CaO—Al 2 O 3 heat insulating material, it is necessary to make CaO / Al 2 O 3 in the range of 0.5 to 2.0, and CaO / Al 2 O 3 is 0.5. If the temperature is less than or more than 2.0, the heat retaining material has a melting temperature of not less than 1536 ° C. of the steel and hardly melts. In addition, the melting temperature of the heat insulating material is set to a temperature when the temperature of the heat insulating material tablet having a diameter of 10 mm × 10 mm is raised in a heating furnace and the height of the heat insulating material tablet is halved. Furthermore, when Ti is added to the CaO-Al 2 O 3 heat insulating material, oxygen that has partially penetrated into the region where the heat insulating material is in an unmelted state is fixed as Ti TiO 2. It is possible to reliably shut off the air after considering the above. The heat insulating material is thrown into the tundish by hand, and the heat insulating material thickness is not uniform depending on the location in the tundish, and the molten state is not constant. The oxygen fixation effect greatly improves the air blocking effect of the heat insulating material.
上記組成のTi含有CaO−Al2O3系保温材を用いて連続鋳造すると、CaF2添加の低融点保温材よりは耐火物溶損は軽減されるが、鋳造時間が長い場合、例えば250分を超えるような長時間鋳造時にはタンディッシュ耐火物溶損の問題は解決されないことが判明した。そこで、保温材を低融点化し、且つ鋳造時間が長い場合にもタンディッシュ耐火物を溶損させない成分条件を検討した結果、CaO/Al2O3を1.1〜2.0の範囲に縮小し、且つMgOを10質量%以上30質量%未満含有させることが有効であることを見いだした。CaO/Al2O3を1.1未満と2.0超の範囲で、MgOが加わるとTi含有CaO−MgO−Al2O3系保温材の溶融温度が上昇し、タンディッシュ内で溶融しにくくなるため、CaO/Al2O3を1.1〜2.0にする必要がある。また、MgOが10質量%未満では、250分を超える長時間鋳造でタンディッシュ耐火物の溶損が進行するため、またMgOが30質量%以上ではTi含有CaO−MgO−Al2O3液相中にMgOが析出して保温材が一部凝固するため、MgO含有率は10質量%以上30質量%未満にする必要がある。したがって、SiO2含有率を5質量%以下、CaO/Al2O3を質量比で1.1〜2.0、MgO含有率を10質量%以上30質量%未満、且つTiを含有した溶鋼表面保温材とすることにより、空気酸化、保温材と溶鋼との反応およびタンディッシュ耐火物の溶損に起因する溶鋼汚染を確実に防止できる。 When continuous casting is performed using the Ti-containing CaO—Al 2 O 3 type heat insulating material having the above composition, the refractory melt damage is reduced as compared with the CaF 2 added low melting point heat insulating material. It has been found that the problem of tundish refractory erosion cannot be solved when casting over a long time. Therefore, as a result of investigating the component conditions that do not cause the tundish refractory to melt even when the heat insulating material has a low melting point and the casting time is long, CaO / Al 2 O 3 is reduced to a range of 1.1 to 2.0. In addition, it has been found that it is effective to contain 10% by mass or more and less than 30% by mass of MgO. When CaO / Al 2 O 3 is less than 1.1 and more than 2.0 and MgO is added, the melting temperature of the Ti-containing CaO—MgO—Al 2 O 3 heat insulating material rises and melts in the tundish. to become Nikuku, it is necessary to the CaO / Al 2 O 3 on 1.1 to 2.0. Further, when MgO is less than 10% by mass, the tundish refractory is melted by casting for a long time exceeding 250 minutes, and when MgO is 30% by mass or more, a Ti-containing CaO—MgO—Al 2 O 3 liquid phase. Since MgO precipitates therein and the heat insulating material partially solidifies, the MgO content needs to be 10% by mass or more and less than 30% by mass. Therefore, the molten steel surface containing SiO 2 content of 5% by mass or less, CaO / Al 2 O 3 by mass ratio of 1.1 to 2.0, MgO content of 10% by mass to less than 30% by mass, and containing Ti. By using the heat insulating material, it is possible to reliably prevent molten steel contamination caused by air oxidation, reaction between the heat insulating material and the molten steel, and melting of the tundish refractory.
保温材中にTiを添加すると空気と反応してTiO2を生成するため、鋳造初期を除いてTi含有CaO−MgO−Al2O3系保温材中にはTiO2が含有される。TiO2は保温材の粘性を低下させ、溶鋼表面上での保温材の広がり性を向上させるため、より均一な保温材被覆状態が得られ易くなる。このため、CaO−MgO−Al2O3を主成分(合計で50%以上を目安)とするTi含有の保温材中に予めTiO2を含有させておくと、鋳造初期からTiO2の低粘性化効果により保温材の被覆性が向上する。 When Ti is added to the heat insulating material, it reacts with air to generate TiO 2, and thus the Ti-containing CaO—MgO—Al 2 O 3 heat insulating material contains TiO 2 except in the initial stage of casting. Since TiO 2 lowers the viscosity of the heat insulating material and improves the spreadability of the heat insulating material on the molten steel surface, it becomes easier to obtain a more uniform heat insulating material coating state. For this reason, if TiO 2 is contained in advance in a Ti-containing heat insulating material containing CaO—MgO—Al 2 O 3 as a main component (50% or more in total), the low viscosity of TiO 2 from the beginning of casting. The covering effect of the heat insulating material is improved by the effect of the heat treatment.
CaO−MgO−Al2O3系保温材へのTiの好ましい添加範囲は0.1〜10質量%である。Tiの含有率が0.1質量%未満では空気中の酸素と反応し難く、反対に10質量%超では溶鋼中にTiが一部溶解し、溶鋼中でのTi濃度上昇やチタニア系介在物生成を引き起こすためである。 The preferable addition range of Ti to the CaO—MgO—Al 2 O 3 heat insulating material is 0.1 to 10% by mass. If the Ti content is less than 0.1% by mass, it is difficult to react with oxygen in the air. Conversely, if it exceeds 10% by mass, Ti partially dissolves in the molten steel, and the Ti concentration in the molten steel increases and titania inclusions. This is to cause generation.
また、CaO−MgO−Al2O3を主成分とするTi含有保温材へのTiO2の好ましい添加範囲は2.0〜30質量%である。TiO2の含有率が2質量%未満ではTi−CaO−Al2O3系保温材の粘性が低下し難く、反対に30質量%超では溶鋼中のAlとTiO2が反応してAl2O3系介在物を少量ではあるが生成し易いためである。 Also preferred range of addition of the TiO 2 to Ti-containing heat insulating material composed mainly of CaO-MgO-Al 2 O 3 is 2.0 to 30 mass%. When the content of TiO 2 is less than 2% by mass, the viscosity of the Ti—CaO—Al 2 O 3 heat insulating material is difficult to decrease, whereas when it exceeds 30% by mass, Al in the molten steel reacts with TiO 2 to react with Al 2 O. This is because it is easy to produce a 3 system inclusion although it is a small amount.
保温材の基本組成は以上に述べた通りであるが、本発明品の機能を低下させない範囲であれば、ZrO2等の他の酸化物やCaCl2等の非酸化物を添加することも可能である。 The basic composition of the heat insulating material is as described above, but other oxides such as ZrO 2 and non-oxides such as CaCl 2 can be added as long as the function of the product of the present invention is not deteriorated. It is.
本発明の保温材はCaO原料、Al2O3原料、TiO2原料、Ti原料等を本発明で規定の成分となるように配合し、均一に混じるように混錬することにより製造される。 The heat insulating material of the present invention is produced by blending a CaO raw material, an Al 2 O 3 raw material, a TiO 2 raw material, a Ti raw material or the like so as to become the specified components in the present invention and kneading them so as to be uniformly mixed.
本発明の保温材をタンディッシュ内の溶鋼表面上に添加して鋼の連続鋳造を行うと、空気酸化と、保温材と溶鋼との反応に起因する溶鋼汚染を確実に防止でき、その上でタンディッシュ耐火物の溶損も生じない。また、本発明の保温材は液相で低粘性であるため、熱間でタンディッシュを繰り返し使用する場合にも、保温材の排滓性が非常に向上するといった利点もある。 When the heat insulating material of the present invention is added onto the surface of the molten steel in the tundish and the continuous casting of the steel is performed, contamination of the molten steel due to air oxidation and the reaction between the heat insulating material and the molten steel can be reliably prevented, and then No tundish refractory melts. In addition, since the heat insulating material of the present invention is low-viscosity in the liquid phase, there is an advantage that the heat-removing material can be greatly improved even when the tundish is repeatedly used in the hot state.
さらに、本発明の保温材をタンディッシュ内に添加して、予め真空脱ガス装置内でTi脱酸された溶鋼を鋳造すると、保温材中Tiの溶解および、保温材中TiO2と溶鋼中Tiとの反応は何れも起こり難いため、本発明の保温材はTi脱酸溶鋼の鋳造に最適な組成となっている。 Furthermore, when the heat insulating material of the present invention is added to the tundish and the molten steel deoxidized in advance in a vacuum degassing apparatus is cast, melting of Ti in the heat insulating material and TiO 2 in the heat insulating material and Ti in the molten steel Therefore, the heat insulating material of the present invention has an optimal composition for casting of Ti deoxidized molten steel.
以下に、実施例及び比較例を挙げて、本発明について説明する。 Hereinafter, the present invention will be described with reference to examples and comparative examples.
(実施例1)
3質量%SiO2、42質量%CaO、30質量%Al2O3、20質量%MgO、5質量%Tiの保温材400kgを容量60tのタンディッシュに添加し、炭素濃度0.04質量%の低炭アルミキルド溶鋼を400分間鋳造した。なお、タンディッシュ内の溶鋼温度は1558℃である。鋳造寸法は、厚み245mm×幅1500mmで、8500mm長さに切断して1コイル単位とした。このスラブを常法により熱間圧延、冷間圧延し、最終的に厚み0.7mm×幅1500mmコイルの冷延鋼板とした。
Example 1
400 kg of a heat insulating material of 3% by mass SiO 2 , 42% by mass CaO, 30% by mass Al 2 O 3 , 20% by mass MgO, 5% by mass Ti is added to a tundish with a capacity of 60 t, and the carbon concentration is 0.04% by mass. Low-carbon aluminum killed molten steel was cast for 400 minutes. In addition, the molten steel temperature in a tundish is 1558 degreeC. Casting dimensions were 245 mm thickness x 1500 mm width, and were cut into 8500 mm lengths to make one coil unit. This slab was hot-rolled and cold-rolled by a conventional method to finally form a cold-rolled steel sheet having a thickness of 0.7 mm × width of 1500 mm coil.
保温材の空気酸化防止効果、溶鋼との反応防止効果および耐火物溶損防止効果は、定常鋳造領域でタンディッシュ入側と出側の溶鋼をサンプリングし、ガス分析を行うことにより測定したタンディッシュ入側と出側の溶鋼中の全酸素濃度の上昇量、及び冷延鋼板の1コイル当たりに発生した表面欠陥の目視観察による発生個数により評価した。 The antioxidation effect of the thermal insulation material, the reaction prevention effect with molten steel, and the refractory refractory prevention effect were measured by sampling the molten steel on the inlet and outlet sides of the tundish in the steady casting region and performing gas analysis. The evaluation was made based on the amount of increase in the total oxygen concentration in the molten steel on the entry side and the exit side, and the number of surface defects generated per one coil of the cold-rolled steel sheet by visual observation.
本発明の保温材により空気酸化、保温材による溶鋼酸化およびタンディッシュ耐火物溶損による溶鋼汚染が防止された結果、タンディッシュ入側と出側の全酸素濃度は0.0037質量%と0.0030質量%で全酸素濃度の上昇はなかった。また、表面欠陥の発生もなかった。 As a result of prevention of air oxidation, molten steel oxidation by the heat insulating material, and molten steel contamination by tundish refractory erosion damage by the heat insulating material of the present invention, the total oxygen concentration on the tundish inlet side and outlet side is 0.0037% by mass. There was no increase in the total oxygen concentration at 0030 mass%. Further, no surface defects were generated.
(実施例2)
2質量%SiO2、40質量%CaO、21質量%Al2O3、12質量%MgO、20質量%TiO2、5質量%Ti保温材400kgを容量60tのタンディッシュに添加し、炭素濃度0.003質量%の極低炭Ti脱酸溶鋼を400分間鋳造した。なお、タンディッシュ内の溶鋼温度は1560℃である。鋳造寸法は、厚み245mm×幅1500mmで、8500mm長さに切断して1コイル単位とした。このスラブを常法により熱間圧延、冷間圧延し、最終的に厚み0.7mm×幅1500mmコイルの冷延鋼板とした。
(Example 2)
400 kg of 2% by mass SiO 2 , 40% by mass CaO, 21% by mass Al 2 O 3 , 12% by mass MgO, 20% by mass TiO 2 , 5% by mass Ti heat insulating material was added to a tundish with a capacity of 60 t, and the carbon concentration was 0 0.003 mass% ultra-low carbon Ti deoxidized molten steel was cast for 400 minutes. In addition, the molten steel temperature in a tundish is 1560 degreeC. Casting dimensions were 245 mm thickness x 1500 mm width, and were cut into 8500 mm lengths to make one coil unit. This slab was hot-rolled and cold-rolled by a conventional method to finally obtain a cold-rolled steel sheet having a thickness of 0.7 mm and a width of 1500 mm.
本発明の保温材により空気酸化と保温材による溶鋼汚染が防止され、且つ耐火物の溶損も抑制された結果、タンディッシュ入側と出側の溶鋼中の全酸素濃度は0.0040質量%と0.0032質量%で全酸素濃度の上昇はなかった。また、表面欠陥の発生もなかった。 As a result of preventing the oxidation of the molten steel by air oxidation and the heat insulating material by the heat insulating material of the present invention and suppressing the refractory erosion, the total oxygen concentration in the molten steel on the entry side and the outlet side of the tundish is 0.0040% by mass. There was no increase in the total oxygen concentration at 0.0032 mass%. Further, no surface defects were generated.
(比較例1)
100質量%MgOの保温材400kgを容量60tのタンディッシュに添加し、炭素濃度0.04質量%の低炭アルミキルド鋼を400分間鋳造した。鋳造寸法は、厚み245mm×幅1500mmで、8500mm長さに切断して1コイル単位とした。このスラブを常法により熱間圧延、冷間圧延し、最終的に厚み0.7mm×幅1500mmコイルの冷延鋼板とした。
(Comparative Example 1)
400 kg of a heat retention material of 100% by mass MgO was added to a tundish having a capacity of 60 t, and low carbon aluminum killed steel having a carbon concentration of 0.04% by mass was cast for 400 minutes. Casting dimensions were 245 mm thickness x 1500 mm width, and were cut into 8500 mm lengths to make one coil unit. This slab was hot-rolled and cold-rolled by a conventional method to finally obtain a cold-rolled steel sheet having a thickness of 0.7 mm and a width of 1500 mm.
MgO系の従来保温材を使用したため、保温材層を通して酸素が侵入し、溶鋼の再酸化が生じた結果、タンディッシュ入側から出側にかけて溶鋼中の全酸素濃度が0.0036質量%から0.0060質量%まで上昇した。また、表面欠陥も平均で6個/コイル発生した。 Since MgO-based conventional heat insulating material is used, oxygen enters through the heat insulating material layer and reoxidation of the molten steel occurs. As a result, the total oxygen concentration in the molten steel from 0.0036% by mass to 0% from the tundish inlet side to the outlet side. It increased to 0060% by mass. In addition, the average number of surface defects was 6 / coil.
(比較例2)
20質量%SiO2、80質量%MgOの保温材400kgを容量60tのタンディッシュに添加し、炭素濃度0.0028質量%の極低炭アルミキルド鋼を400分間鋳造した。鋳造寸法は、厚み245mm×幅1500mmで、8500mm長さに切断して1コイル単位とした。このスラブを常法により熱間圧延、冷間圧延し、最終的に厚み0.7mm×幅1500mmコイルの冷延鋼板とした。
(Comparative Example 2)
400 kg of a heat insulating material of 20% by mass SiO 2 and 80% by mass MgO was added to a tundish having a capacity of 60 t, and an ultra low carbon aluminum killed steel having a carbon concentration of 0.0028% by mass was cast for 400 minutes. Casting dimensions were 245 mm thickness x 1500 mm width, and were cut into 8500 mm lengths to make one coil unit. This slab was hot-rolled and cold-rolled by a conventional method to finally obtain a cold-rolled steel sheet having a thickness of 0.7 mm and a width of 1500 mm.
SiO2を含有するMgO系の従来保温材を使用したため、空気による溶鋼の再酸化と、保温材中SiO2と溶鋼との反応により溶鋼汚染が生じた結果、タンディッシュ入側から出側にかけて溶鋼中の全酸素濃度が0.003質量%から0.0059質量%まで上昇した。また、表面欠陥も平均で8個/コイル発生した。 Because MgO-based conventional heat insulating material containing SiO 2 was used, molten steel was contaminated by reoxidation of molten steel by air and reaction between SiO 2 and molten steel in the heat insulating material, resulting in molten steel from the tundish inlet side to the outlet side. The total oxygen concentration inside increased from 0.003 mass% to 0.0059 mass%. In addition, an average of 8 surface defects / coil was generated.
(比較例3)
16質量%SiO2、58質量%CaO、26質量%Al2O3の保温材400kgを容量60tのタンディッシュに添加し、炭素濃度0.0028質量%の極低炭アルミキルド鋼を400分間鋳造した。鋳造寸法は、厚み245mm×幅1500mmで、8500mm長さに切断して1コイル単位とした。このスラブを常法により熱間圧延、冷間圧延し、最終的に厚み0.7mm×幅1500mmコイルの冷延鋼板とした。
(Comparative Example 3)
400 kg of a heat insulating material of 16% by mass SiO 2 , 58% by mass CaO, 26% by mass Al 2 O 3 was added to a tundish having a capacity of 60 t, and a very low carbon aluminum killed steel having a carbon concentration of 0.0028% by mass was cast for 400 minutes. . Casting dimensions were 245 mm thickness x 1500 mm width, and were cut into 8500 mm lengths to make one coil unit. This slab was hot-rolled and cold-rolled by a conventional method to finally obtain a cold-rolled steel sheet having a thickness of 0.7 mm and a width of 1500 mm.
SiO2を含有する高CaO−低Al2O3系の保温材を使用したため、空気による溶鋼の再酸化と、保温材中SiO2と溶鋼との反応により溶鋼汚染が生じた結果、タンディッシュ入側から出側にかけて溶鋼中の全酸素濃度が0.0032質量%から0.0062質量%まで上昇した。また、表面欠陥も平均で8.2個/コイル発生した。
Since a high CaO-low Al 2 O 3 type heat insulating material containing SiO 2 was used, molten steel was contaminated by reoxidation of the molten steel by air and reaction between SiO 2 and the molten steel in the heat insulating material. The total oxygen concentration in the molten steel increased from 0.0032 mass% to 0.0062 mass% from the side to the outlet side. In addition, an average of 8.2 surface defects / coil was generated.
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JP2009197285A (en) * | 2008-02-22 | 2009-09-03 | Nippon Steel Corp | Method for producing high clean steel slab |
JP2019000903A (en) * | 2017-06-12 | 2019-01-10 | Jfeスチール株式会社 | Smelting method and continuous casting method of steel |
CN110666112A (en) * | 2019-09-25 | 2020-01-10 | 安徽省含山县华平铸造厂(普通合伙) | Heat-insulating covering agent for molten iron |
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JP2009197285A (en) * | 2008-02-22 | 2009-09-03 | Nippon Steel Corp | Method for producing high clean steel slab |
JP2019000903A (en) * | 2017-06-12 | 2019-01-10 | Jfeスチール株式会社 | Smelting method and continuous casting method of steel |
CN110666112A (en) * | 2019-09-25 | 2020-01-10 | 安徽省含山县华平铸造厂(普通合伙) | Heat-insulating covering agent for molten iron |
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