JP6668941B2 - Continuous casting of molten steel - Google Patents

Continuous casting of molten steel Download PDF

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JP6668941B2
JP6668941B2 JP2016102359A JP2016102359A JP6668941B2 JP 6668941 B2 JP6668941 B2 JP 6668941B2 JP 2016102359 A JP2016102359 A JP 2016102359A JP 2016102359 A JP2016102359 A JP 2016102359A JP 6668941 B2 JP6668941 B2 JP 6668941B2
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恭平 田島
恭平 田島
近藤　泰光
泰光 近藤
信輔 渡辺
信輔 渡辺
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本発明は、溶鋼の連続鋳造方法に関し、詳細には、硫黄含有率が高い溶鋼の連続鋳造方法に関する。   The present invention relates to a continuous casting method for molten steel, and more particularly, to a continuous casting method for molten steel having a high sulfur content.

硫黄系快削鋼など硫黄含有率が高い鋼の被削性（切削加工するときの削られやすさ）は、鋼材中に生成されるＭｎＳ系介在物の粒子サイズに依存し、ＭｎＳ系介在物の粒子サイズが大きいほど、被削性が向上することが知られている。   The machinability of steel with a high sulfur content such as sulfur-based free-cutting steel (easiness of cutting when cutting) depends on the particle size of MnS-based inclusions formed in the steel material, and MnS-based inclusions It is known that the larger the particle size of is, the more the machinability is improved.

例えば、特許文献１では、連続鋳造法により硫黄系快削鋼を製造するにあたり、連続鋳造機の２次冷却帯における比水量を０．５Ｌ（リットル）／ｋｇ以下とすることにより、ＭｎＳ系介在物の成長を促進させる方法が開示されている。
特許文献１によれば、連続鋳造法により硫黄系快削鋼を製造する際に、凝固過程及びその後の冷却過程にある鋳片内各部位の冷却速度を低下させることによって硫黄系快削鋼内のＭｎＳ系介在物を大型化することが可能であるとされている。 For example, in Patent Literature 1, when producing a sulfur-based free-cutting steel by a continuous casting method, the specific water amount in a secondary cooling zone of a continuous casting machine is set to 0.5 L (liter) / kg or less, so that MnS-based Methods for promoting the growth of objects are disclosed.
According to Patent Literature 1, when a sulfur-based free-cutting steel is manufactured by a continuous casting method, the cooling rate of each part in a slab during a solidification process and a subsequent cooling process is reduced, thereby reducing the sulfur-based free-cutting steel. It is said that it is possible to increase the size of MnS-based inclusions.

また、特許文献２では、連続鋳造法により硫黄含有量０．０８〜０．４０％の硫黄系快削鋼を製造するに際し、鋳型へ注入する溶鋼のトータル酸素量を２５０ｐｐｍ以上にして鋳造し、且つ、鋳片が凝固する際、鋳片幅中央の断面内の鋳片表面と断面中央の中間点において、液相線温度〜１４００℃の温度区間の平均冷却速度を５０℃／分以下とする方法が開示されている。
特許文献２によれば、凝固する際の酸素量を高めることはＭｎＳの大型化のみならず、ＭｎＳ中のＦｅ含有量を減少させる効果を有し、その両方の効果により成品の被削性を大幅に改善でき、さらに鋳片が凝固する際の液相線温度〜１４００℃の温度区間の冷却速度を減少することにより、ＭｎＳ成長の律速段階であるＭｎの固相内拡散が促進されＭｎＳの成長を促すことができるとされている。 Further, in Patent Document 2, when producing a sulfur-based free-cutting steel having a sulfur content of 0.08 to 0.40% by a continuous casting method, casting is performed by setting the total oxygen amount of molten steel to be injected into a mold to 250 ppm or more, In addition, when the slab is solidified, the average cooling rate in the temperature range from the liquidus temperature to 1400 ° C. is set to 50 ° C./min or less at the midpoint between the slab surface and the center of the slab in the slab width center. A method is disclosed.
According to Patent Literature 2, increasing the amount of oxygen during solidification not only increases the size of MnS, but also has the effect of reducing the Fe content in MnS, and both effects reduce the machinability of the product. By greatly reducing the cooling rate in the temperature range from the liquidus temperature to 1400 ° C. when the slab is solidified, diffusion of Mn in the solid phase, which is the rate-determining step of MnS growth, is promoted, and MnS It is said that growth can be promoted.

特公平３−４６２１９号公報Japanese Patent Publication No. 3-46219 特開平５−７７０１２号公報JP-A-5-77012

硫黄を０．２０〜０．８０質量％含有する鋼は、温度が低下するにつれて脆化が顕著となる。具体的には、鋳片の表面温度が１０００℃以下になると鋳片の脆化が生じ、９００℃以下で鋳片の脆化が顕著となる。垂直曲げ型若しくは湾曲型の連続鋳造機では、湾曲した鋳片を真っ直ぐにする曲げ戻し矯正が必要となるが、曲げ戻し矯正時の鋳片温度が脆化温度域の場合、鋳片表面に割れが発生する。そのため、２次冷却水量を低減し、鋳片の表面温度を脆化温度域よりも高温に保持することが行われている。   Steel containing 0.20 to 0.80% by mass of sulfur becomes remarkably embrittled as the temperature decreases. Specifically, when the surface temperature of the slab becomes 1000 ° C. or less, the slab becomes brittle, and at 900 ° C. or less, the slab becomes remarkably embrittled. In a vertical bending type or curved type continuous casting machine, it is necessary to straighten a curved slab and straighten it.However, if the slab temperature at the time of skewing is in the brittle temperature range, the surface of the slab may crack. Occurs. Therefore, the amount of secondary cooling water is reduced, and the surface temperature of the slab is kept higher than the embrittlement temperature range.

２次冷却水量を低減すると、鋳片の表面温度が高温に保たれ、鋳片の表面割れは防止できるが、鋳片表面の高温化と、２次冷却水量の低減による大気接触面積の増大により、鋳片表面の酸化が促進され、酸化スケールの生成量が増加する。特許文献１や特許文献２記載の技術では２次冷却水量を抑制しているため、酸化スケールが大量に発生する。   When the amount of secondary cooling water is reduced, the surface temperature of the slab is maintained at a high temperature, and the surface cracks of the slab can be prevented. However, by increasing the surface temperature of the slab and increasing the contact area with the atmosphere by reducing the amount of secondary cooling water. In addition, oxidation of the slab surface is promoted, and the amount of oxide scale generated increases. In the techniques described in Patent Literature 1 and Patent Literature 2, a large amount of oxide scale is generated because the amount of secondary cooling water is suppressed.

一般に、酸化スケールの生成量が増加しても、鋳片に酸化スケールが密着しているため、鋳片から酸化スケールが容易に剥離することはないが、硫黄を０．２０〜０．８０質量％含有する溶鋼の場合、以下の現象が起きることを本発明者らは発見した。即ち、硫黄を０．２０〜０．８０質量％含有する溶鋼の場合、鋳片と酸化スケールの界面において、硫黄が濃化して鉄と硫黄の二元系共晶化合物が生成する。鉄と硫黄の二元系共晶化合物の共晶温度は９００〜１０００℃の温度域に存在し、鋳片の表面温度が共晶温度以上であると、共晶化合物は溶融して融液となり、酸化スケールは鋳片から容易に剥離する。多量の酸化スケールが鋳片から剥離して落下すると、落下した酸化スケールが連続鋳造機内に堆積して鋳造ロールへの噛み込み等が発生し、鋳片品質の劣化が生じる。   In general, even if the amount of oxide scale generated increases, the oxide scale is in close contact with the slab, so the oxide scale does not easily separate from the slab, but the sulfur content is 0.20 to 0.80 mass. The present inventors have found that the following phenomena occur in the case of molten steel containing%. That is, in the case of molten steel containing 0.20 to 0.80 mass% of sulfur, sulfur is concentrated at the interface between the slab and the oxide scale, and a binary eutectic compound of iron and sulfur is generated. The eutectic temperature of the binary eutectic compound of iron and sulfur exists in the temperature range of 900 to 1000 ° C. If the surface temperature of the slab is higher than the eutectic temperature, the eutectic compound melts and becomes a melt. In addition, the oxide scale easily peels from the slab. When a large amount of oxide scale is peeled off from the slab and falls, the dropped oxide scale accumulates in the continuous casting machine and bites into casting rolls, etc., and the slab quality is deteriorated.

本発明はかかる事情に鑑みてなされたもので、硫黄含有率が高い溶鋼の連続鋳造において、連続鋳造機内への酸化スケ−ルの落下堆積によるマシントラブルの発生を防止すると共に、従来に比べて鋳片表面の割れを抑制することを目的とする。   The present invention has been made in view of such circumstances, and in the continuous casting of molten steel having a high sulfur content, the occurrence of machine trouble due to the falling and depositing of an oxide scale in a continuous casting machine is prevented, and the present invention is compared with the related art. The purpose is to suppress cracks on the slab surface.

上記目的を達成するため、本発明は、硫黄を０．２０〜０．８０質量％含有する溶鋼を連続鋳造する方法であって、
連続鋳造鋳型直下０ｍの位置をＡ、連続鋳造鋳型直下から鋳片に沿って下流側に２ｍの位置をＢ、連続鋳造鋳型直下から鋳片に沿って下流側に４ｍの位置をＣとし、
前記Ａから前記Ｂの範囲において鋳片を冷却する水量を鋳片表面の単位面積（ｍ ２ ）当たり２００Ｌ（リットル）以上とし、
前記Ｂから前記Ｃの範囲において鋳片を冷却する水量を鋳片表面の単位面積（ｍ ２ ）当たり１３０Ｌ（リットル）以上とし、
前記Ｃから鋳片の曲げ戻しを行う矯正部までの範囲において鋳片に供給する平均水量を鋳片表面の単位面積（ｍ ２ ）当たり０．６Ｌ（リットル）／ｍｉｎ以下とすることを特徴としている。 In order to achieve the above object, the present invention provides a method for continuously casting molten steel containing 0.20 to 0.80 mass% of sulfur,
A is a position 0 m below the continuous casting mold, B is a position 2 m downstream from the continuous casting mold along the slab, C is a position 4 m downstream from the casting mold immediately below the slab.
In the range of A to B, the amount of water for cooling the slab is 200 L (liter) or more per unit area (m 2 ) of the slab surface ;
In the range of B to C, the amount of water for cooling the slab is 130 L (liter) or more per unit area (m 2 ) of the slab surface ,
The average amount of water supplied to the slab in the range from the C to the straightening section where the slab is bent back is 0.6 L (liter) / min or less per unit area (m 2 ) of the slab surface. I have.

前述したように、硫黄を０．２０〜０．８０質量％含有する溶鋼を連続鋳造する際に鋳片表面に生成する酸化スケールは、鋳片の表面温度が共晶温度（例えば９００〜１０００℃）以上であると、鋳片と酸化スケールの界面に生成した融液によって鋳片から容易に剥離落下する。   As described above, the oxide scale generated on the slab surface during continuous casting of molten steel containing 0.20 to 0.80% by mass of sulfur is such that the surface temperature of the slab is eutectic (for example, 900 to 1000 ° C.). With the above, the melt generated at the interface between the slab and the oxide scale easily separates and drops from the slab.

連続鋳造機において酸化スケールが剥離落下しやすい領域はＢからＣの範囲である。本発明では、鋳片がＢを通過するまでに、鋳片の表面温度が共晶温度未満となるように鋳片を冷却し、ＢからＣの範囲において鋳片の表面温度が共晶温度未満を維持するように鋳片を冷却する。これにより、ＢからＣの範囲における融液及び酸化スケールの生成を抑制して、酸化スケールの落下堆積によるマシントラブルの発生を防止する。   In the continuous casting machine, the area where the oxide scale is likely to peel off falls from B to C. In the present invention, the slab is cooled so that the surface temperature of the slab is lower than the eutectic temperature before the slab passes through B, and the surface temperature of the slab is lower than the eutectic temperature in the range of B to C. Cool the slab to maintain Thereby, the generation of the melt and the oxide scale in the range of B to C is suppressed, and the occurrence of machine trouble due to the fall-down of the oxide scale is prevented.

ＡからＢの範囲の水量は、鋳片がＢを通過するまでに、鋳片の表面温度を共晶温度未満に冷却できる水量であればよく、ＡからＢの範囲を通過する鋳片に供給する水量を、鋳片表面の単位面積（ｍ ２ ）当たり２００Ｌ（リットル）以上とすれば、鋳片がＢを通過するまでに、鋳片の表面温度を共晶温度未満とすることができる。
また、ＢからＣの範囲の水量は、この間において鋳片の表面温度を共晶温度未満に維持できる水量であればよく、この間を通過する鋳片に供給する水量を、鋳片表面の単位面積（ｍ ２ ）当たり１３０Ｌ（リットル）以上とすれば、ＢからＣの範囲において鋳片の表面温度を共晶温度未満に維持することができる。 The amount of water in the range from A to B may be any amount of water that can cool the surface temperature of the slab to below the eutectic temperature before the slab passes through B, and is supplied to the slab passing through the range from A to B. If the amount of water to be applied is 200 L (liter) or more per unit area (m 2 ) of the slab surface, the surface temperature of the slab can be lower than the eutectic temperature before the slab passes B.
Further, the amount of water in the range from B to C may be any amount of water that can maintain the surface temperature of the slab below the eutectic temperature during this period. The amount of water supplied to the slab passing therethrough is determined by the unit area of the slab surface . When it is set to 130 L (liter) or more per (m 2 ), the surface temperature of the slab can be maintained below the eutectic temperature in the range of B to C.

一方、Ｃから矯正部までの範囲では、鋳片の曲げ戻し矯正時における鋳片の脆化度合を軽減して鋳片の表面割れを抑制することを目的とする。そのため、Ｃから矯正部までの範囲において鋳片表面を均一に復熱させ、鋳片表面を脆化温度を超える温度とする。従って、Ｃから矯正部までの範囲において鋳片に供給する水量は、この間に亘って鋳片表面温度の復熱を促す程度の量であることが望ましく、Ｃから矯正部までの範囲において鋳片に供給する平均水量を鋳片表面の単位面積（ｍ ２ ）当たり０．６Ｌ（リットル）／ｍｉｎ以下とすればよい。 On the other hand, in the range from C to the straightening portion, an object is to reduce the degree of brittleness of the slab at the time of straightening of the slab to reduce the surface crack of the slab. Therefore, the slab surface is uniformly reheated in the range from C to the straightening portion, and the slab surface is set to a temperature exceeding the embrittlement temperature. Therefore, the amount of water supplied to the slab in the range from C to the straightening portion is desirably an amount that promotes the reheating of the slab surface temperature during this period. The average amount of water supplied to the slab may be 0.6 L (liter) / min or less per unit area (m 2 ) of the slab surface .

本発明に係る溶鋼の連続鋳造方法では、硫黄を０．２０〜０．８０質量％含有する溶鋼を連続鋳造する際に、酸化スケールが剥離落下しやすい領域における鋳片の表面温度を、融液が生成される共晶温度未満とすることにより、融液及び酸化スケールの生成量を抑制して酸化スケ−ルの落下堆積によるマシントラブルの発生を防止すると共に、連続鋳造鋳型直下から鋳片に沿って下流側に４ｍの位置から矯正部までの範囲において鋳片表面を均一に復熱させることにより、鋳片の表面割れを抑制する。   In the continuous casting method for molten steel according to the present invention, when continuously casting molten steel containing 0.20 to 0.80% by mass of sulfur, the surface temperature of the slab in a region where the oxide scale is likely to peel off and fall is set to The temperature is below the eutectic temperature at which is generated, thereby suppressing the generation of melt and oxide scale, preventing the occurrence of machine troubles due to the fall-down of the oxide scale, and forming the cast slab from immediately below the continuous casting mold. The surface crack of the slab is suppressed by uniformly recovering the surface of the slab in a range from the position of 4 m downstream to the straightening portion.

本発明の一実施の形態に係る溶鋼の連続鋳造方法に使用される垂直曲げ型連続鋳造機の模式図である。BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram of the vertical bending type continuous casting machine used for the continuous casting method of the molten steel which concerns on one Embodiment of this invention.

続いて、添付した図面を参照しつつ、本発明を具体化した実施の形態について説明し、本発明の理解に供する。   Next, embodiments of the present invention will be described with reference to the accompanying drawings to provide an understanding of the present invention.

本発明の一実施の形態に係る溶鋼の連続鋳造方法に使用される連続鋳造機１０の模式図を図１に示す。連続鋳造機１０では、精錬が終了した溶鋼１９から鋳片２０が連続的に製造され、所定の長さに切断される。
精錬が終了した溶鋼１９は、連続鋳造機１０の最上部に配置された取鍋１１に貯留された後、取鍋１１の底部に設けられたノズル孔（図示省略）に装着されたロングノズル１２を介して、取鍋１１の下方に配置されたタンディッシュ１３内に注入される。タンディッシュ１３内に注入された溶鋼１９は、タンディッシュ１３内で介在物が除去された後、タンディッシュ１３の底部に設けられたノズル孔（図示省略）に装着された浸漬ノズル１４を介して、タンディッシュ１３の下方に配置された連続鋳造鋳型１５（以下では、単に「鋳型」と呼ぶ。）内に注入される。鋳型１５は常時、水冷されており、鋳型１５に流入した溶鋼１９は鋳型１５に接触して急冷され、微細なチル晶からなる薄い凝固殻を形成する。 FIG. 1 is a schematic view of a continuous casting machine 10 used in a method for continuously casting molten steel according to an embodiment of the present invention. In the continuous casting machine 10, a slab 20 is continuously manufactured from the molten steel 19 after the refining and cut to a predetermined length.
After the refining of the molten steel 19 is stored in the ladle 11 disposed at the top of the continuous casting machine 10, the long nozzle 12 attached to the nozzle hole (not shown) provided at the bottom of the ladle 11. Is poured into the tundish 13 arranged below the ladle 11. After the inclusions are removed in the tundish 13, the molten steel 19 injected into the tundish 13 passes through the immersion nozzle 14 attached to a nozzle hole (not shown) provided at the bottom of the tundish 13. Is poured into a continuous casting mold 15 (hereinafter simply referred to as “mold”) arranged below the tundish 13. The mold 15 is always water-cooled, and the molten steel 19 flowing into the mold 15 contacts the mold 15 and is rapidly cooled to form a thin solidified shell made of fine chill crystals.

鋳型１５の下方には、サポートロール、ガイドロール、及びピンチロールからなる複数対の鋳造ロール１６が鋳造経路に沿って配置されている。本実施の形態における連続鋳造機１０の方式は垂直曲げ型であり、鋳型１５に続く鋳造経路は、下流側に向かって、鋳片２０が鉛直下方に移動する垂直部と、鋳片２０を円弧状に湾曲させる円弧部と、円弧状となった鋳片２０を真っ直ぐにする矯正部１８とを備えている。
また、鋳造方向に隣接する鋳造ロール１６の間隙には、水スプレーノズルなどの冷却ノズル１７を有する２次冷却帯が配置されている。 Below the mold 15, a plurality of pairs of casting rolls 16 including a support roll, a guide roll, and a pinch roll are arranged along a casting path. The method of the continuous casting machine 10 in the present embodiment is a vertical bending die, and the casting path following the casting mold 15 is formed by a vertical section where the slab 20 moves vertically downward toward the downstream side, and An arc portion to be curved in an arc shape and a straightening portion 18 for straightening the arc shaped cast piece 20 are provided.
A secondary cooling zone having a cooling nozzle 17 such as a water spray nozzle is arranged in a gap between the casting rolls 16 adjacent to each other in the casting direction.

未凝固溶鋼を内蔵したまま鋳型１５を出た鋳片２０は、冷却ノズル１７で水冷されつつ、鋳造ロール１６により下方に搬送された後、鋳片切断機（図示省略）により所定の長さに切断される。   The slab 20 leaving the mold 15 with the unsolidified molten steel contained therein is conveyed downward by the casting roll 16 while being cooled with water by the cooling nozzle 17, and then reduced to a predetermined length by a slab cutting machine (not shown). Be cut off.

次に、上記構成を有する連続鋳造機１０を用いて、本実施の形態に係る溶鋼の連続鋳造方法について説明する。   Next, a method of continuously casting molten steel according to the present embodiment using continuous casting machine 10 having the above configuration will be described.

対象とする溶鋼１９は、硫黄を０．２０〜０．８０質量％含有する溶鋼である。
硫黄を０．２０〜０．８０質量％含有する溶鋼の場合、鋳片と酸化スケールの界面において、硫黄が濃化して鉄と硫黄の二元系共晶化合物が生成し、鋳片の表面温度が共晶温度（例えば９００〜１０００℃）以上であると、共晶化合物は溶融して融液となる。 The target molten steel 19 is a molten steel containing 0.20 to 0.80% by mass of sulfur.
In the case of molten steel containing 0.20 to 0.80% by mass of sulfur, sulfur is concentrated at the interface between the slab and the oxide scale to form a binary eutectic compound of iron and sulfur, and the surface temperature of the slab Is higher than the eutectic temperature (for example, 900 to 1000 ° C.), the eutectic compound melts to form a melt.

本実施の形態では、２次冷却帯において鋳片２０に供給する水量を以下のように設定する。なお、以降の説明では、便宜上、鋳型１５直下０ｍの位置をＡ、鋳型１５直下から鋳片２０に沿って下流側に２ｍの位置をＢ、鋳型１５直下から鋳片２０に沿って下流側に４ｍの位置をＣとする（図１参照）。   In the present embodiment, the amount of water supplied to the slab 20 in the secondary cooling zone is set as follows. In the following description, for convenience, the position of 0 m directly below the mold 15 is A, the position of 2 m is directly below the mold 15 along the slab 20, and the position of 2 m is downstream from just below the mold 15, and the downstream is along the slab 20. The position at 4 m is designated as C (see FIG. 1).

［Ａ〜Ｂの範囲］
鋳片２０を冷却する水量を鋳片２０の単位面積当たり２００Ｌ（リットル）以上とする。
鋳型１５直下の鋳片２０の表面温度は１２００〜１３００℃程度であり、地鉄が酸化され酸化スケールが生成する。生成する酸化スケールは上述した二元系共晶化合物を含み、二元系共晶化合物は共晶温度以上で溶融して融液となる。
Ａ〜Ｂの範囲において上記水量で鋳片２０を冷却することにより、鋳片２０の表面温度は速やかに共晶温度未満となり、融液及び酸化スケールの生成量を抑制することができる。 [Range of AB]
The amount of water for cooling the slab 20 is set to 200 L (liter) or more per unit area of the slab 20.
The surface temperature of the slab 20 immediately below the mold 15 is about 1200 to 1300 ° C., and the ground iron is oxidized to generate an oxide scale. The generated oxide scale contains the above-mentioned binary eutectic compound, and the binary eutectic compound melts at a temperature higher than the eutectic temperature to become a melt.
By cooling the slab 20 with the above amount of water in the range of A to B, the surface temperature of the slab 20 quickly becomes lower than the eutectic temperature, and the amount of melt and oxide scale generated can be suppressed.

水量の上限値は特に規定しないが、一般的な連続鋳造機における冷却水の供給量を踏まえると、鋳片２０の単位面積当たり４００Ｌ（リットル）程度である。
一方、鋳片２０に供給する水量が鋳片２０の単位面積当たり２００Ｌ（リットル）未満であると、鋳片２０の表面温度が共晶温度未満に低下しない領域が発生する。その結果、融液が生成する部分が生じ、酸化スケールの剥離落下を抑制できないことがある。 Although the upper limit of the water amount is not particularly defined, it is about 400 L (liter) per unit area of the slab 20 in consideration of the supply amount of cooling water in a general continuous casting machine.
On the other hand, if the amount of water supplied to the slab 20 is less than 200 L (liter) per unit area of the slab 20, a region where the surface temperature of the slab 20 does not drop below the eutectic temperature occurs. As a result, a portion where a melt is generated may occur, and it may not be possible to prevent the oxide scale from peeling and falling.

［Ｂ〜Ｃの範囲］
鋳片２０を冷却する水量を鋳片２０の単位面積当たり１３０Ｌ（リットル）以上とする。
垂直曲げ型や湾曲型の連続鋳造機は、Ａ〜Ｃの範囲において鋳片が鉛直若しくは概ね鉛直となるため、Ｂ〜Ｃの範囲において酸化スケールが剥離落下しやすい。多量の酸化スケールが剥離落下した場合、落下した酸化スケールが連続鋳造機内に堆積して鋳造ロールへの酸化スケールの噛み込みが発生する。そのため、Ｂ〜Ｃの範囲において鋳片２０の表面温度を融液の生成が抑制される温度に維持する必要がある。
Ｂ〜Ｃの範囲において上記水量で鋳片２０を冷却することにより、鋳片２０の表面温度の上昇（復熱）が抑制され、鋳片２０の表面温度を、融液の生成が抑制される温度（例えば１０００℃未満さらには９００℃未満）に維持することができる。 [Range of BC]
The amount of water for cooling the slab 20 is set to 130 L (liter) or more per unit area of the slab 20.
In the vertical bending type or curved type continuous casting machine, the slab is vertical or substantially vertical in the range of A to C, so that the oxide scale is easily peeled and dropped in the range of B to C. When a large amount of oxide scale is separated and dropped, the dropped oxide scale is deposited in the continuous casting machine, and the oxide scale is caught in the casting roll. Therefore, in the range of B to C, it is necessary to maintain the surface temperature of the slab 20 at a temperature at which generation of a melt is suppressed.
By cooling the slab 20 with the amount of water in the range of B to C, the rise (recuperation) of the surface temperature of the slab 20 is suppressed, and the surface temperature of the slab 20 is reduced to suppress the generation of a melt. The temperature can be maintained (eg, less than 1000 ° C., and even less than 900 ° C.).

水量の上限値は特に規定しないが、一般的な連続鋳造機における冷却水の供給量を踏まえると、鋳片２０の単位面積当たり４００Ｌ（リットル）程度である。
一方、鋳片２０に供給する水量が鋳片２０の単位面積当たり１３０Ｌ（リットル）未満であると、鋳片２０の表面温度が上昇して融液が生成され、酸化スケールの剥離落下を抑制することができない。 Although the upper limit of the water amount is not particularly defined, it is about 400 L (liter) per unit area of the slab 20 in consideration of the supply amount of cooling water in a general continuous casting machine.
On the other hand, if the amount of water supplied to the slab 20 is less than 130 L (liter) per unit area of the slab 20, the surface temperature of the slab 20 rises and a melt is generated, thereby suppressing peeling and falling off of the oxide scale. Can not do.

［Ｃ〜矯正部１８までの範囲］
Ｃ〜矯正部１８までの範囲において鋳片２０に供給する平均水量を鋳片２０の単位面積当たり０．６Ｌ（リットル）／ｍｉｎ以下とする。
垂直曲げ型や湾曲型の連続鋳造機では、湾曲した鋳片２０を矯正部１８で真っ直ぐに曲げ戻す必要がある。その際、鋳片２０の表面温度が脆化温度域にあると、鋳片に表面割れが発生し、品質異常が発生するおそれがある。硫黄を０．２０〜０．８０質量％含有する溶鋼１９の場合、鋳片２０の表面温度が１０００℃以下になると鋳片２０の脆化が生じ、９００℃以下で鋳片２０の脆化が顕著となる。
そのため、Ｃ〜矯正部１８までの範囲において鋳片表面を均一に復熱させ、鋳片表面を脆化温度を超える温度とする。 [Range from C to straightening unit 18]
The average amount of water supplied to the slab 20 in the range from C to the straightening unit 18 is set to 0.6 L (liter) / min or less per unit area of the slab 20.
In a vertical bending type or bending type continuous casting machine, it is necessary to straightly bend the curved slab 20 by the straightening unit 18. At that time, if the surface temperature of the slab 20 is in the embrittlement temperature range, surface slabs may occur in the slab, and abnormal quality may occur. In the case of molten steel 19 containing 0.20 to 0.80% by mass of sulfur, when the surface temperature of the slab 20 becomes 1000 ° C. or lower, the slab 20 becomes brittle, and at 900 ° C. or lower, the slab 20 becomes brittle. Will be noticeable.
Therefore, the surface of the slab is uniformly reheated in the range from C to the correction section 18, and the surface of the slab is set to a temperature exceeding the embrittlement temperature.

Ｃ〜矯正部１８までの範囲において鋳片２０に供給する平均水量を上記水量とすることにより、鋳片表面を均一に復熱させ、鋳片２０の曲げ戻し矯正時における脆化度合を軽減することができる。その結果、鋳片２０の顕著な表面割れを抑制して、工業的に採用可能な割れ発生頻度に低減することができる。   By setting the average amount of water supplied to the slab 20 in the range from C to the straightening unit 18 to the above-mentioned water amount, the slab surface is uniformly reheated, and the degree of embrittlement at the time of straightening the slab 20 is reduced. be able to. As a result, remarkable surface cracks of the slab 20 can be suppressed, and the frequency of occurrence of cracks that can be industrially adopted can be reduced.

なお、Ｃ〜矯正部１８までの範囲において鋳片２０に供給する平均水量の下限値はゼロＬ（リットル）である。即ち、水を供給しなくてもよい。
一方、鋳片２０に供給する平均水量を鋳片２０の単位面積当たり０．６Ｌ（リットル）／ｍｉｎ超とすると、鋳片２０から抜熱が発生し、矯正部１８における鋳片２０の表面割れが顕著となる。 Note that the lower limit of the average amount of water supplied to the slab 20 in the range from C to the straightening unit 18 is zero L (liter). That is, it is not necessary to supply water.
On the other hand, when the average amount of water supplied to the slab 20 exceeds 0.6 L (liter) / min per unit area of the slab 20, heat is removed from the slab 20 and the surface crack of the slab 20 in the straightening unit 18 is generated. Is remarkable.

以上、本発明の一実施の形態について説明してきたが、本発明は何ら上記した実施の形態に記載の構成に限定されるものではなく、特許請求の範囲に記載されている事項の範囲内で考えられるその他の実施の形態や変形例も含むものである。例えば、上記実施の形態では、連続鋳造機の方式を垂直曲げ型としているが、湾曲型でも良い。   As described above, one embodiment of the present invention has been described. However, the present invention is not limited to the configuration described in the above-described embodiment, but may be implemented within the scope of matters described in the claims. Other possible embodiments and modifications are also included. For example, in the above embodiment, the continuous casting machine is a vertical bending type, but may be a curved type.

本発明の効果について検証するために実施した検証試験について説明する。
使用する連続鋳造機は垂直曲げ型とし、Ａ〜Ｂの範囲、Ｂ〜Ｃの範囲、及びＣ〜矯正部までの範囲における各水量（水温：２０〜３０℃）をパラメータとして、硫黄を０．４０〜０．５０質量％含有する快削鋼を製造した。試験結果の一覧を表１に示す。 A verification test performed to verify the effect of the present invention will be described.
The continuous casting machine to be used is a vertical bending type, and the amount of sulfur is set to 0.1 as a parameter with each amount of water (water temperature: 20 to 30 ° C.) in the range from A to B, the range from B to C, and the range from C to the straightening section. A free-cutting steel containing 40 to 0.50% by mass was produced. Table 1 shows a list of the test results.

なお、試験結果は、連続鋳造機内への酸化スケールの堆積の程度、及び鋳片の表面割れの程度によって評価した。具体的には以下のように評価した。
酸化スケールについては、鋳型直下から下流側４ｍ付近に存在する幅１０ｃｍのチャンネル（連続鋳造機のフレーム）上への酸化スケールの落下状況を評価し、チャンネルの全面に酸化スケールが落下している場合を×（不可）、酸化スケールがチャンネルに落下していないか、酸化スケールが落下していてもチャンネル全面を覆っていない場合を○（良）とした。
また、鋳片の表面割れについては、鋳片を分塊圧延した後の鋼片の表面検査によって評価した。鋼片１本当たりの表面疵の個数が従来例のバラツキ範囲を超える場合を×（不可）、従来例と同程度以下の場合を○（良）とした。 The test results were evaluated based on the degree of deposition of the oxide scale in the continuous casting machine and the degree of surface cracking of the slab. Specifically, evaluation was made as follows.
Regarding the oxide scale, evaluate the situation of the oxide scale falling onto a 10 cm wide channel (frame of a continuous casting machine) that is located just below the mold and about 4 m downstream, and when the oxide scale falls on the entire surface of the channel. Was evaluated as x (impossible), and the case where the oxide scale did not fall on the channel or the oxide scale did not cover the entire surface of the channel even when the scale was falling was evaluated as ○ (good).
The surface cracks of the slab were evaluated by surface inspection of the slab after slab rolling. The case where the number of surface flaws per steel slab exceeds the variation range of the conventional example was evaluated as x (impossible), and the case where the number of surface flaws was equal to or less than the conventional example was evaluated as ○ (good).

Figure 0006668941
Figure 0006668941

同表より以下のことがわかる。
・Ａ〜Ｂの範囲における水量が２００Ｌ／ｍ２以上且つＢ〜Ｃの範囲における水量が１３０Ｌ／ｍ２以上であった実施例及び比較例３は、酸化スケールの堆積が少なかったが、この条件を満足しなかった比較例１、２、及び従来例は酸化スケールの堆積が多かった。
・Ｃ〜矯正部までの範囲における平均水量が０．６Ｌ／（ｍ２・ｍｉｎ）以下であった実施例及び比較例１、２は表面割れが従来例と同程度以下であったが、この条件を満足しなかった比較例３は表面割れが従来例より悪かった。 The table shows the following.
In Examples and Comparative Example 3 in which the amount of water in the range A to B was 200 L / m 2 or more and the amount of water in the range B to C was 130 L / m 2 or more, the accumulation of oxide scale was small. In Comparative Examples 1 and 2, which did not satisfy the above, and the conventional example, the deposition of oxide scale was large.
-In Examples and Comparative Examples 1 and 2 in which the average amount of water in the range from C to the straightening portion was 0.6 L / (m 2 · min) or less, the surface cracks were about the same as or less than the conventional example. Comparative Example 3, which did not satisfy the conditions, had worse surface cracks than the conventional example.

１０：連続鋳造機、１１：取鍋、１２：ロングノズル、１３：タンディッシュ、１４：浸漬ノズル、１５：鋳型（連続鋳造鋳型）、１６：鋳造ロール、１７：冷却ノズル、１８：矯正部、１９：溶鋼、２０：鋳片 10: continuous casting machine, 11: ladle, 12: long nozzle, 13: tundish, 14: immersion nozzle, 15: mold (continuous casting mold), 16: casting roll, 17: cooling nozzle, 18: straightening unit, 19: molten steel, 20: cast slab

Claims (1)

硫黄を０．２０〜０．８０質量％含有する溶鋼を連続鋳造する方法であって、
連続鋳造鋳型直下０ｍの位置をＡ、連続鋳造鋳型直下から鋳片に沿って下流側に２ｍの位置をＢ、連続鋳造鋳型直下から鋳片に沿って下流側に４ｍの位置をＣとし、
前記Ａから前記Ｂの範囲において鋳片を冷却する水量を鋳片表面の単位面積（ｍ ２ ）当たり２００Ｌ（リットル）以上とし、
前記Ｂから前記Ｃの範囲において鋳片を冷却する水量を鋳片表面の単位面積（ｍ ２ ）当たり１３０Ｌ（リットル）以上とし、
前記Ｃから鋳片の曲げ戻しを行う矯正部までの範囲において鋳片に供給する平均水量を鋳片表面の単位面積（ｍ ２ ）当たり０．６Ｌ（リットル）／ｍｉｎ以下とすることを特徴とする溶鋼の連続鋳造方法。 A method for continuously casting molten steel containing 0.20 to 0.80% by mass of sulfur,
A is a position 0 m below the continuous casting mold, B is a position 2 m downstream from the continuous casting mold along the slab, C is a position 4 m downstream from the casting mold immediately below the slab.
The amount of water for cooling the slab in the range from A to B is 200 L (liter) or more per unit area (m 2 ) of the slab surface ,
In the range of B to C, the amount of water for cooling the slab is 130 L (liter) or more per unit area (m 2 ) of the slab surface ,
The average amount of water supplied to the slab in the range from the C to the straightening part where the slab is bent back is set to 0.6 L (liter) / min or less per unit area (m 2 ) of the slab surface. Continuous casting method for molten steel.
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