JP5157664B2 - Continuous casting method of round slabs for seamless steel pipes - Google Patents

Continuous casting method of round slabs for seamless steel pipes Download PDF

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JP5157664B2
JP5157664B2 JP2008156201A JP2008156201A JP5157664B2 JP 5157664 B2 JP5157664 B2 JP 5157664B2 JP 2008156201 A JP2008156201 A JP 2008156201A JP 2008156201 A JP2008156201 A JP 2008156201A JP 5157664 B2 JP5157664 B2 JP 5157664B2
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正道 阿部
康一 堤
龍郎 勝村
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Jfeスチール株式会社
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本発明は、継目無鋼管用丸鋳片の連続鋳造方法に関し、詳しくは、連続鋳造ままの内部品質では継目無鋼管用素材として問題のある炭素濃度の高い炭素鋼や合金鋼などの丸鋳片、及び、鋳造ままの状態では熱間加工性が悪く、継目無鋼管用素材としては使用できなかったCr含有鋼の丸鋳片の内部品質を改善するための連続鋳造方法に関するものである。   The present invention relates to a continuous casting method for a round cast slab for a seamless steel pipe, and more specifically, a round slab such as carbon steel or alloy steel having a high carbon concentration, which has a problem as a material for a seamless steel pipe in the internal quality as continuously cast. Further, the present invention relates to a continuous casting method for improving the internal quality of a round slab of Cr-containing steel, which is poor in hot workability as it is cast and cannot be used as a material for seamless steel pipes.
継目無鋼管は、一般的に、継目無鋼管用素材として丸ビレットを使用し、この丸ビレットをマンネスマン穿孔法などを用いて中空の素管に穿孔し、その後、エロンゲータ、プラグミルまたはマンドレルミルなどの圧延機により延伸し、仕上げ工程としてサイザーやストレッチレデューサにより定径化する工程を経て製造されている。この継目無鋼管用の丸ビレットとしては、低炭素鋼のように比較的簡単に内質の優れた丸鋳片を連続鋳造により製造可能な鋼種の場合には、鋳造ままの丸鋳片が用いられる。しかし、ステンレス鋼などの熱間加工性に劣るCr含有鋼種の場合は、鋳造ままの丸鋳片を用いると、マンネスマン穿孔時に素管の内面に疵が発生する。   A seamless steel pipe generally uses a round billet as a material for a seamless steel pipe, and the round billet is drilled into a hollow raw pipe using a Mannesmann drilling method or the like. It is manufactured through a process of stretching with a rolling mill and making the diameter constant with a sizer or stretch reducer as a finishing process. As a round billet for seamless steel pipes, as-cast round slabs are used in the case of steel types that can be produced by continuous casting of round cast slabs with excellent internal quality, such as low carbon steel. It is done. However, in the case of a Cr-containing steel type that is inferior in hot workability, such as stainless steel, if an as-cast round slab is used, flaws are generated on the inner surface of the raw tube during Mannesmann drilling.
Cr含有鋼の熱間加工性が劣る主な原因は、Cr量の増加に起因して連続鋳造時に偏析やポロシティが鋳片軸芯部に発生しやすく、内質の劣った丸鋳片になるためである。熱間加工性に特に大きな悪影響を与えるポロシティは、凝固収縮により丸鋳片の最終凝固部に発生する空隙に、粘度が高いなどの理由により、溶鋼が供給され難いことによって発生する。   The main cause of inferior hot workability of Cr-containing steel is that due to the increase in Cr content, segregation and porosity are likely to occur in the slab shaft core during continuous casting, resulting in a round slab with inferior internal quality. Because. Porosity that has a particularly large adverse effect on hot workability is caused by the difficulty in supplying molten steel to the voids generated in the final solidified portion of the round cast slab due to solidification shrinkage due to high viscosity.
図7は、溶鋼中のCr濃度と溶鋼の粘度との関係を示したものであり、溶鋼中のCr濃度の増加に伴って溶鋼の粘度が増すこと、及び、13質量%前後のCr濃度で粘度はピークを示すことが分かる。また、図8は、Cr濃度の少ない領域における、溶鋼中のCr濃度と溶鋼の粘度との関係を示したものであり、Cr濃度が0.5質量%を越えると粘度の上昇が顕著になることが分かる。   FIG. 7 shows the relationship between the Cr concentration in the molten steel and the viscosity of the molten steel. The increase in the viscosity of the molten steel with the increase in the Cr concentration in the molten steel and the Cr concentration around 13% by mass. It can be seen that the viscosity shows a peak. FIG. 8 shows the relationship between the Cr concentration in the molten steel and the viscosity of the molten steel in a region where the Cr concentration is low. When the Cr concentration exceeds 0.5 mass%, the increase in viscosity becomes significant. I understand that.
上記のような内部欠陥を有する丸鋳片に対して、過酷な加工方法であるマンネスマン穿孔を行うと、素管の内面には、ポロシティや偏析に起因した疵が発生する。このため、Crを含有する鋼種においては、内部品質を向上させるための圧延工程を経て製造された丸鋼片を継目無鋼管用素材として用いることが必須とされてきた。つまり、連続鋳造ままの丸鋳片を用いて製管すると、内面疵の発生が懸念される場合には、鋼塊(インゴット)或いは連続鋳造鋳片を分塊圧延してポロシティを機械的に圧着させ、内部品質の優れた丸鋼片を得ることで、この問題を回避していた。尚、本発明における丸ビレットとは、横断面が円形の鋼片及び鋳片の両者を差し、鋼片とは分塊圧延などの圧延工程を経て得られるもの、鋳片とは連続鋳造したままのものである。   When Mannesmann drilling, which is a severe processing method, is performed on a round slab having internal defects as described above, wrinkles due to porosity and segregation are generated on the inner surface of the raw tube. For this reason, in steel types containing Cr, it has been essential to use round steel pieces produced through a rolling process for improving internal quality as a material for seamless steel pipes. In other words, if there is concern about the occurrence of inner surface flaws when pipes are produced using round cast slabs as continuously cast, the ingot or ingot or continuous cast slabs are subjected to ingot rolling to mechanically crimp the porosity. This problem was avoided by obtaining round steel pieces with excellent internal quality. The round billet in the present invention refers to both a steel slab and a cast slab having a circular cross section, and the steel slab is obtained through a rolling process such as partial rolling, and is continuously cast with the slab. belongs to.
例えば、特許文献1には、Cr含有鋼の大断面の連続鋳造スラブから方形断面のブルームを熱間圧延して製造する中間段階を経て、このブルームに再度熱間圧延を施して継目無ステンレス鋼管用丸ビレットを製造する技術が開示されている。   For example, Patent Document 1 discloses that a seamless stainless steel pipe is obtained by performing hot rolling again on a bloom from a continuous casting slab with a large cross section of Cr-containing steel by hot rolling and producing a bloom with a square cross section. A technique for manufacturing a round billet is disclosed.
しかしながら、連続鋳造鋳片に熱間圧延を施すと、圧延後の鋼片の端面が凹凸のある形状となることから、継目無鋼管用素材の丸ビレットにするためには、端面の形状を整えるための切断工程が必須となる。即ち、端部の切断によりクロップが必然的に発生し、製品歩留が低下する。また、当然ながら、熱間圧延を行うための再加熱も、製品コストを増大させる。従って、特許文献1に提案される方法は、経済性から見ると優れた解決策とはいえない。   However, when hot rolling is performed on a continuous cast slab, the end face of the rolled steel slab has an uneven shape. Therefore, in order to obtain a round billet of a seamless steel pipe material, the shape of the end face is adjusted. Therefore, a cutting process is essential. In other words, cropping is inevitably generated by cutting the end portion, and the product yield is lowered. Of course, reheating for hot rolling also increases product costs. Therefore, the method proposed in Patent Document 1 is not an excellent solution from the viewpoint of economy.
そこで、圧延工程を経ずに丸鋳片をそのまま継目無鋼管用素材とするべく、丸鋳片の内質を向上させる技術が提案されている。丸鋳片の内質を向上させる手段としては、先ず、鋳造中の電磁攪拌処理技術がある(例えば、特許文献2を参照)。但し、この技術は広く実施されているものの、その効果はポロシティの発生を防止するほどは大きくない。   Therefore, a technique for improving the inner quality of the round slab has been proposed in order to use the round slab as a raw material for seamless steel pipes without going through a rolling process. As means for improving the quality of a round slab, first, there is an electromagnetic stirring treatment technique during casting (see, for example, Patent Document 2). However, although this technique is widely implemented, its effect is not so great as to prevent the occurrence of porosity.
連続鋳造鋳片の内質を向上させる他の手段として、鋳造中のインライン軽圧下法或いは大圧下法が広く採用されている。特許文献3や特許文献4に開示されている技術がこれにあたる。これらの技術は、スラブやブルームの内質改善方法として良く知られており、ポロシティの消滅や偏析の低減化が可能である。鋳造中或いは鋳造直後に加工を加えるため再加熱が不要であり、結果的に製造コストも低減できる技術である。   As another means for improving the quality of the continuous cast slab, an in-line light reduction method or a large reduction method during casting is widely adopted. The techniques disclosed in Patent Document 3 and Patent Document 4 correspond to this. These techniques are well known as methods for improving the quality of slabs and blooms, and can eliminate porosity and reduce segregation. This is a technique in which reheating is unnecessary because processing is performed during casting or immediately after casting, and as a result, the manufacturing cost can be reduced.
しかしながら、丸鋳片に対して、例えば、スラブ鋳片などの板状鋳片を圧下するために用いるような、鋳片の移送方向に対しての垂直断面が矩形である、平型のロールにより圧下を加えると、ロールに接触した部分は平面化し、他方、ロールに接触していない部分は膨らみ、丸鋳片の断面形状は偏平化し、更には角形に近づく。断面形状が角形に近づくと、丸鋳片の回転を利用するマンネスマン穿孔時の噛み込みが不安定になるなどの操業上の問題が発生するのみならず、マンネスマン穿孔後の素管及び最終製品である継目無鋼管の管軸方向に対しての垂直断面(以下、「C断面」と記す)での肉厚変動(偏肉)が大きくなる。   However, with a round roll having a rectangular vertical cross-section with respect to the direction in which the slab is transferred, such as used for rolling down a plate slab such as a slab slab, for example, When the reduction is applied, the portion that is in contact with the roll is flattened, while the portion that is not in contact with the roll is inflated, the cross-sectional shape of the round cast piece is flattened, and further approaches a square shape. When the cross-sectional shape approaches a square shape, not only will operational problems occur, such as instability of biting during Mannesmann drilling using the rotation of round slabs, but in the tube and final product after Mannesmann drilling. The wall thickness variation (unevenness) in a vertical section (hereinafter referred to as “C section”) of a seamless steel pipe with respect to the pipe axis direction increases.
この問題に対し、特許文献5には、楕円形鋳型により断面形状が楕円形の鋳片を得て、それを、ラウンド孔型ロールにより長径方向に圧下し、真円断面の鋳片を得る技術が開示されている。この方法は圧下後の鋳片形状の問題は解決しているが、鋳造時の湯流れが真円断面の鋳型(円形鋳型)を用いた場合に比較して不均一になり、それに起因する湯面変動やモールドパウダーの巻き込みが、新たな欠陥の原因になる。また、必要な圧下量に対応して鋳型を数多く準備する必要があること、及び、内部品質に問題の無い鋼種の場合も圧下をかけることになり、コストが上昇することなどの問題もあり、やはり有効な解決策ではない。   In order to solve this problem, Patent Document 5 discloses a technique for obtaining a slab having an elliptical cross section by using an elliptical mold, and rolling the slab in a major axis direction by a round hole type roll. Is disclosed. Although this method solves the problem of slab shape after rolling, the molten metal flow during casting becomes non-uniform compared to the case of using a mold with a circular cross section (circular mold), and the resulting molten metal. Surface fluctuations and mold powder entrainment cause new defects. In addition, it is necessary to prepare a large number of molds corresponding to the required reduction amount, and in the case of a steel type that does not have a problem with internal quality, there is also a problem such as cost increase, After all it is not an effective solution.
また、特許文献6には、圧下ロールとして、カリバー底の開き角度δが70°以上115°以下である鞍型ロールを用い、円形鋳型により鋳造された連続鋳造中の丸鋳片に圧下を加える技術が開示されている。この技術は、圧下後鋳片の断面形状の確保及び内部品質の向上を或る程度両立させているが、更なる内部品質の向上のためには、圧下量を増大させることが必要で、圧下量の増大に伴って丸鋳片の偏平率が増大し、丸鋳片の断面形状の確保が困難となる。
特開昭61−140301号公報 特開昭60−54251号公報 特開昭49−121738号公報 特開昭63−183765号公報 特開平7−108358号公報 特開平10−34304号公報
Further, in Patent Document 6, a vertical roll having a caliber bottom opening angle δ of 70 ° or more and 115 ° or less is used as a reduction roll, and the reduction is applied to a round cast piece continuously cast by a circular mold. Technology is disclosed. Although this technology achieves a certain degree of securing the cross-sectional shape of the slab after rolling and improving the internal quality to some extent, in order to further improve the internal quality, it is necessary to increase the rolling amount. As the amount increases, the flatness of the round slab increases, and it becomes difficult to ensure the cross-sectional shape of the round slab.
JP 61-140301 A JP 60-54251 A JP 49-121738 A JP-A 63-183765 JP-A-7-108358 Japanese Patent Laid-Open No. 10-34304
上記説明のように、熱間加工性に劣る鋼、特にCr含有鋼などの合金元素の多い鋼において、鋳造ままの丸鋳片をそのまま継目無鋼管用素材とするべく、内部品質の優れた丸鋳片を、丸鋳片の形状を大きく劣化させることなく且つ経済性に優れた方法で製造する手段が切望されていたにも拘わらず、従来、有効な手段はなく、鋼塊或いは連続鋳造鋳片を分塊圧延して継目無鋼管用素材とすることによるコスト上昇や、鋳造ままの丸鋳片を継目無鋼管用素材とすることによる継目無鋼管での内面疵の発生を余儀なくされていた。   As described above, in steels with a lot of alloying elements such as steels with poor hot workability, especially Cr-containing steels, in order to use as-cast round slabs as raw materials for seamless steel pipes, Despite the long-awaited means for producing slabs by a method that does not greatly deteriorate the shape of round slabs and is economical, there has been no effective means in the past. The cost was increased by rolling the piece into a seamless steel pipe material, and it was forced to generate inner surface flaws in the seamless steel pipe by using an as-cast round cast piece as the seamless steel pipe material. .
本発明は上記事情に鑑みてなされたもので、その目的とするところは、熱間加工性の劣る鋼、特にCr含有鋼などの合金元素の多い鋼であっても、内部品質に優れていて、鋳造ままの丸鋳片をそのまま継目無鋼管用素材とすることのできる丸鋳片を、丸鋳片の断面形状を劣化させることなく且つ経済的に安定して製造するための、継目無鋼管用丸鋳片の連続鋳造方法を提供することである。   The present invention has been made in view of the above circumstances, and the object of the present invention is excellent in internal quality even in steels with a lot of alloying elements such as steel having poor hot workability, particularly Cr-containing steel. A seamless steel pipe for producing a round cast piece that can be used as it is as a raw material for a seamless steel pipe as it is, without causing deterioration of the cross-sectional shape of the round cast piece and economically stably. It is providing the continuous casting method of the round cast slab.
上記課題を解決するための本発明に係る継目無鋼管用丸鋳片の連続鋳造方法は、円形鋳型による連続鋳造中の丸鋳片に、該丸鋳片の凝固完了点近傍に設置した一対の鞍型ロールにより圧下を加え、該圧下の直前及び/または後に、連続鋳造中の丸鋳片を強制冷却することを特徴とするものである。   A continuous casting method for seamless steel pipe round slabs according to the present invention for solving the above-described problems is a pair of round slabs in the vicinity of a solidification completion point of the round slabs. The rolling is applied by a vertical roll, and the round slab during continuous casting is forcibly cooled immediately before and / or after the rolling.
本発明によれば、従来は困難であった、Cr含有鋼などの難加工性鋼種の連続鋳造による継目無鋼管用丸鋳片の製造が、連続鋳造設備に大きな変更を加えることなく可能となる。丸鋳片の断面形状を損ねることなく、また、寸法精度も従来と変わらない状態で、内部品質の大幅に改善された丸鋳片が製造可能になることにより、付加価値の高いCr含有鋼の継目無鋼管の製造コストの低減が可能になることの意義は極めて大きい。   According to the present invention, it is possible to produce a round slab for a seamless steel pipe by continuous casting of difficult-to-work steel grades such as Cr-containing steel, which has been difficult in the past, without greatly changing the continuous casting equipment. . It is possible to manufacture round slabs with greatly improved internal quality without losing the cross-sectional shape of the round slabs, and with the same dimensional accuracy as before. Significantly, it is possible to reduce the manufacturing cost of seamless steel pipes.
また、通常の炭素鋼などの連続鋳造ままの継目無鋼管用丸鋳片の製造においても、低コストで内部品質の大幅な改善が得られ、それにより、製品歩留りの向上及び生産能率の向上などの大きな効果がもたらされる。   In addition, in the production of round cast slabs for seamless steel pipes such as ordinary carbon steel, the internal quality can be greatly improved at a low cost, thereby improving product yield and production efficiency. The big effect is brought about.
以下、添付図面を参照して本発明を具体的に説明する。図1は、本発明の実施形態の1例を示す図であり、内部品質が良好で、熱間加工性に優れた継目無鋼管用丸鋳片を連続鋳造により製造する状況を示す概略図である。   Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a diagram illustrating an example of an embodiment of the present invention, and is a schematic diagram illustrating a situation in which a round cast piece for a seamless steel pipe having good internal quality and excellent hot workability is manufactured by continuous casting. is there.
図1において、符号1は内部空間横断面が真円である円形鋳型、2は円形鋳型の下方に配置されるガイドロール、3は丸鋳片を引抜くためのピンチロール、4は未凝固溶鋼層を攪拌するための電磁攪拌装置、5は丸鋳片に圧下力を付与するための圧下ロール、6は圧下された丸鋳片を強制冷却するためのスプレーノズル、6’は圧下の直前の丸鋳片を強制冷却するためのスプレーノズル、7は丸鋳片を所定の長さに切断するための鋳片切断機である。また、ガイドロール2の設置される範囲には、鋳造中の丸鋳片を強制冷却するためのスプレーノズル(図示せず)が配置されて、二次冷却帯を構成している。尚、圧下された丸鋳片を強制冷却するためのスプレーノズル6を、二次冷却帯のスプレーノズルと区別するために、「圧下鋳片冷却用スプレーノズル6」と称す。また、圧下の直前の丸鋳片を強制冷却するためのスプレーノズル6’を、二次冷却帯のスプレーノズルと区別するために、「圧下直前鋳片冷却用スプレーノズル6’」と称す。   In FIG. 1, reference numeral 1 is a circular mold whose inner space cross section is a perfect circle, 2 is a guide roll disposed under the circular mold, 3 is a pinch roll for drawing a round slab, 4 is unsolidified molten steel Electromagnetic stirrer for stirring the layer, 5 is a reduction roll for applying a reduction force to the round slab, 6 is a spray nozzle for forcibly cooling the reduced slab, and 6 'is immediately before the reduction. A spray nozzle 7 for forcibly cooling the round slab, 7 is a slab cutting machine for cutting the round slab into a predetermined length. Further, a spray nozzle (not shown) for forcibly cooling the round slab being cast is arranged in a range where the guide roll 2 is installed, thereby constituting a secondary cooling zone. The spray nozzle 6 for forcibly cooling the rolled slab is referred to as “a slab cooling spray nozzle 6” in order to distinguish it from the spray nozzles in the secondary cooling zone. Further, the spray nozzle 6 'for forcibly cooling the round slab immediately before reduction is referred to as "spray nozzle 6' for slab cooling immediately before reduction" in order to distinguish it from the spray nozzle in the secondary cooling zone.
円形鋳型1の上方に配置されたタンディッシュ(図示せず)から円形鋳型1に注入された溶鋼は、円形鋳型1の内壁に接触して冷却され、円形鋳型1との接触部に外形が円形の凝固シェル10を形成する。そして、外殻を凝固シェル10とし、内部を未凝固溶鋼層9とする丸鋳片8は、ピンチロール3によって円形鋳型1から引抜かれ、次いで、ガイドロール2で支持されながら二次冷却帯で冷却されて凝固シェル10の厚みを増大させ、やがて軸芯部までの凝固を完了する。二次冷却帯に設置された電磁攪拌装置4により、未凝固溶鋼層9は攪拌され、丸鋳片8の軸芯部に等軸晶が形成される。丸鋳片8の軸芯部に等軸晶が形成されることにより、丸鋳片8の軸芯部の偏析及びポロシティは改善されるが、本発明において、電磁攪拌装置4の設置は必須ではなく、本発明を適用することにより、電磁攪拌装置4を設置しなくても、軸芯部の偏析及びポロシティの改善された丸鋳片8を得ることができる。軸芯部までの凝固を完了した丸鋳片8は鋳片切断機7によって所定の長さに切断され、継目無鋼管用丸鋳片が製造される。   The molten steel poured into the circular mold 1 from a tundish (not shown) disposed above the circular mold 1 is cooled by contacting the inner wall of the circular mold 1, and the outer shape is circular at the contact portion with the circular mold 1. The solidified shell 10 is formed. The round slab 8 having the outer shell as the solidified shell 10 and the inside as the unsolidified molten steel layer 9 is pulled out of the circular mold 1 by the pinch roll 3 and then supported by the guide roll 2 in the secondary cooling zone. Cooling increases the thickness of the solidified shell 10 and eventually completes the solidification to the shaft core. The unsolidified molten steel layer 9 is stirred by the electromagnetic stirring device 4 installed in the secondary cooling zone, and equiaxed crystals are formed in the shaft core portion of the round cast slab 8. By forming equiaxed crystals in the shaft core portion of the round slab 8, segregation and porosity of the shaft core portion of the round slab 8 are improved. However, in the present invention, the installation of the electromagnetic stirring device 4 is not essential. In addition, by applying the present invention, it is possible to obtain a round slab 8 with improved segregation and porosity of the shaft core portion without installing the electromagnetic stirring device 4. The round slab 8 that has been solidified to the shaft core is cut into a predetermined length by a slab cutting machine 7 to produce a seamless steel pipe round slab.
本発明においては、丸鋳片8の内部品質を向上させるために、つまり、軸芯部の偏析、ポロシティ及び放射状の軸芯割れを改善するために、ピンチロール3の下流側に設置した圧下ロール5を用いて鋳造中の丸鋳片8を圧下するとともに、圧下ロール5の直前の位置に設置した圧下直前鋳片冷却用スプレーノズル6’及び/または圧下後に圧下ロール5の下流側に設置した圧下鋳片冷却用スプレーノズル6を用いて鋳造中の丸鋳片8を強制冷却する。尚、図1では、丸鋳片8を水平方向に移送しつつ圧下しているが、勿論、丸鋳片8を垂直または斜め方向に移送中に圧下を加えることも可能である。   In the present invention, in order to improve the internal quality of the round cast slab 8, that is, in order to improve segregation, porosity and radial axial core cracking of the shaft core portion, a rolling roll installed on the downstream side of the pinch roll 3 5 is used to lower the round slab 8 being cast, and the spray nozzle 6 ′ for cooling the slab immediately before the reduction roll installed at the position immediately before the reduction roll 5 and / or the downstream side of the reduction roll 5 after the reduction. The round slab 8 being cast is forcibly cooled using the spray nozzle 6 for cooling the slab. In FIG. 1, the round cast slab 8 is rolled down while being transferred in the horizontal direction. Of course, the round cast slab 8 may be rolled down while being transferred vertically or obliquely.
図2に、図1に示す圧下ロール5を用いて鋳造中の丸鋳片8を圧下している状態を斜視図により示す。圧下ロール5としては、図2に示すように、一対の鞍型ロール11,11を用いる。一対の鞍型ロール11,11を用いて圧下することにより、垂直断面が矩形である平型ロールを用いた圧下に比較して、圧下後の丸鋳片8の偏平率εを大きくすることなく、効果的な圧下を加えることができる。ここで、偏平率εは、「偏平率ε(%)={1−(丸鋳片の或る断面中での最短径部長さ)/(同一断面中の最長径部長さ)}×100」で定義される。   FIG. 2 is a perspective view showing a state in which the round slab 8 being rolled is being rolled down using the rolling roll 5 shown in FIG. As the reduction roll 5, as shown in FIG. 2, a pair of vertical rolls 11 and 11 are used. By rolling down using a pair of vertical rolls 11 and 11, the flatness ε of the round cast slab 8 after rolling is not increased as compared with rolling using a flat roll having a rectangular vertical cross section. Can apply effective reduction. Here, the flatness ε is “flatness ε (%) = {1− (the shortest diameter portion length in a certain cross section of a round cast piece) / (longest diameter portion length in the same cross section)} × 100”. Defined by
これは、一対の鞍型ロール11,11を使用することより、ロールと丸鋳片8との接触点が4点となり、ロールが丸鋳片8を拘束しやすくなるため、圧下量を大きくしても偏平率εは大きくならないからである。また、その結果として、偏平化に起因するマンネスマン穿孔時の噛み込み不良などの問題や、穿孔後の素管の偏肉の問題も大幅に小さくなる。   This is because the contact points between the roll and the round slab 8 are four points by using the pair of vertical rolls 11 and 11, and the roll easily restrains the round slab 8, so the amount of reduction is increased. This is because the flatness ε does not increase. As a result, problems such as biting failure at the time of drilling Mannesmann due to flattening, and problems of uneven thickness of the raw tube after drilling are also greatly reduced.
一対の鞍型ロール11,11で圧下する場合に、鞍型ロール11のカリバー底の開き角度δは、圧下を均一にかける観点からは90°が最適である。但し、90°の前後の一定の範囲内の場合は、偏平率εを大きくせずに有効な圧下をかけることができる。その好ましい範囲は、開き角度δが70°以上115°以下の範囲である。開き角度δが70°未満、または、115°を越える場合は、偏平率εが大きくなる。   When the pair of saddle-type rolls 11 and 11 are used for reduction, the opening angle δ of the caliber bottom of the vertical roll 11 is optimally 90 ° from the viewpoint of uniformly applying the reduction. However, in a certain range around 90 °, effective reduction can be applied without increasing the flat rate ε. A preferable range thereof is a range in which the opening angle δ is 70 ° to 115 °. When the opening angle δ is less than 70 ° or exceeds 115 °, the flatness ratio ε increases.
圧下ロール5による圧下は、丸鋳片8の凝固の完了直後または丸鋳片8の凝固が完了する以前に行う必要がある。一方、凝固が余り進んでいない状態で行うと、その後の凝固過程で、ポロシティや偏析が発生するため好ましくない。効果が大きく現れる丸鋳片8の軸芯部の固相率fsの下限は0.3である。即ち、丸鋳片8の軸芯部の30%以上が固相の状態で、圧下を行うことが好ましい。固相率fsが0.3未満の場合は、圧下後に若干のポロシティが発生し、また偏析も大きくなる。   The reduction by the reduction roll 5 needs to be performed immediately after the completion of the solidification of the round slab 8 or before the solidification of the round slab 8 is completed. On the other hand, it is not preferable to perform the solidification in a state where the solidification is not so advanced because porosity and segregation occur in the subsequent solidification process. The lower limit of the solid phase rate fs of the shaft core portion of the round cast slab 8 in which the effect is significant is 0.3. That is, it is preferable to perform the reduction while 30% or more of the shaft core portion of the round cast slab 8 is in a solid state. When the solid phase ratio fs is less than 0.3, some porosity is generated after the reduction, and segregation also increases.
圧下時の固相率fsの上限値は1.0である。即ち、完全に凝固した後も、凝固直後であれば圧下は有効である。従って、固相率fsが0.3以上1.0以下の状態で圧下を行うことが好ましい。固相率は、伝熱計算によって求めることができる。   The upper limit of the solid phase ratio fs during the reduction is 1.0. In other words, the reduction is effective even after the solidification, if it is immediately after the solidification. Therefore, it is preferable to perform the reduction in a state where the solid phase ratio fs is 0.3 or more and 1.0 or less. The solid phase ratio can be obtained by heat transfer calculation.
圧下量は、丸鋳片8の体積減少率で判断する。ここで、丸鋳片8の体積減少率は、「体積減少率=(丸鋳片C断面の面積減少率)×(鋳造速度)」の式で定義する。   The amount of reduction is determined by the volume reduction rate of the round slab 8. Here, the volume reduction rate of the round slab 8 is defined by the formula “volume reduction rate = (area reduction rate of the cross section of the round slab C) × (casting speed)”.
一対の鞍型ロール11,11で圧下する場合には、体積減少率が最大7%までは、偏平率εを過剰に大きくせずに圧下を行うことが可能である。一方、圧下による内面品質の向上効果、即ち、マンネスマン穿孔後の素管の内面疵の発生率は、体積減少率が0.1%以上で発現され、体積減少率の増加とともに内面疵の発生は減少する。従って、一対の鞍型ロール11,11による圧下時の体積減少率の範囲は0.1〜7%となる。   In the case of rolling down with a pair of saddle type rolls 11 and 11, it is possible to perform rolling down without increasing the flat rate ε excessively until the volume reduction rate is up to 7%. On the other hand, the improvement effect of the inner surface quality due to the reduction, that is, the rate of occurrence of inner surface flaws in the tube after Mannesmann drilling is expressed when the volume reduction rate is 0.1% or more. Decrease. Therefore, the range of the volume reduction rate during reduction by the pair of saddle-shaped rolls 11, 11 is 0.1 to 7%.
即ち、上記の範囲内の体積減少率の圧下を、丸鋳片8が上記の固相率fsの状態において、一対の鞍型ロール11,11により加えることにより、圧下の効果が発現される。   That is, the reduction effect of volume reduction within the above range is exerted by the pair of vertical rolls 11 and 11 when the round slab 8 is in the state of the solid phase rate fs described above, and the effect of the reduction is expressed.
そして、この圧下の直前に、圧下直前鋳片冷却用スプレーノズル6’によって丸鋳片8を強制冷却する、及び/または、圧下の後に、丸鋳片8を圧下鋳片冷却用スプレーノズル6で強制冷却することにより、丸鋳片8の内部品質が更に向上する。   Then, immediately before this reduction, the round slab 8 is forcibly cooled by the slab cooling spray nozzle 6 ′ immediately before reduction and / or after the reduction, the round slab 8 is reduced by the reduction slab cooling spray nozzle 6. By forced cooling, the internal quality of the round slab 8 is further improved.
本発明は、直径が340mm以下の丸鋳片8に適用した場合に、その効果が特に顕著に認められる。丸鋳片8の直径が340mmを越える場合は、鋳造時の軸芯部の冷却速度が遅く、ポロシティが生成しにくく、また、熱応力による軸芯割れも起こりにくいためである。また、本発明は鋼種を問わず、丸鋳片8の内質の向上に有効であるが、溶鋼の粘度が高く、鋳造中にポロシティや偏析が発生しやすい鋼種、即ち、0.5質量%を越える量のCrを含有する鋼に適用する場合に、特にその効果が著しい。   When the present invention is applied to the round cast slab 8 having a diameter of 340 mm or less, the effect is particularly noticeable. This is because when the diameter of the round slab 8 exceeds 340 mm, the cooling rate of the shaft core portion during casting is slow, porosity is not easily generated, and shaft core cracking due to thermal stress is unlikely to occur. In addition, the present invention is effective for improving the quality of the round cast slab 8 regardless of the steel type, but the viscosity of the molten steel is high, and the steel type that easily generates porosity and segregation during casting, that is, 0.5% by mass. The effect is particularly remarkable when applied to a steel containing Cr exceeding the above range.
以上説明したように、本発明によれば、従来は困難であった、Cr含有鋼などの難加工性鋼種の連続鋳造による継目無鋼管用丸鋳片の製造が、連続鋳造設備に大きな変更を加えることなく達成される。そして、丸鋳片8の断面形状を損ねることなく、また、寸法精度も従来と変わらない状態で、内部品質の大幅に改善された丸鋳片8が製造可能になることにより、Cr含有鋼などの継目無鋼管の製造コストが低減可能となる。   As described above, according to the present invention, the production of round slabs for seamless steel pipes by continuous casting of difficult-to-process steel grades such as Cr-containing steel, which has been difficult in the past, has greatly changed the continuous casting equipment. Achievable without addition. And since it becomes possible to manufacture the round cast slab 8 with greatly improved internal quality without impairing the cross-sectional shape of the round cast slab 8 and with the same dimensional accuracy as before, Cr-containing steel, etc. The manufacturing cost of the seamless steel pipe can be reduced.
本発明を実施例により更に詳細に説明する。   The present invention will be described in more detail with reference to examples.
図1に示す連続鋳造機を用い、転炉及びRH真空脱ガス装置にて溶製した、Crを13質量%含有する含Cr溶鋼を170mm直径の丸鋳片に鋳造した。そして、開き角度δが90°である、一対の鞍型ロールからなる圧下ロールの配置された位置での丸鋳片軸芯部の固相率が約0.5となるように鋳造速度を調整し、その状態で、一対の鞍型ロールにより丸鋳片を圧下し、その後、圧下鋳片冷却用スプレーノズルから噴霧される冷却水によって、水量密度100リットル/min・m2及び冷却帯長さ3.0mの条件で強制冷却して、継目無鋼管用のCr含有丸鋳片を製造した(本発明例)。 Using the continuous casting machine shown in FIG. 1, molten Cr-containing steel containing 13% by mass of Cr and melted by a converter and an RH vacuum degassing apparatus was cast into a round cast piece having a diameter of 170 mm. Then, the casting speed is adjusted so that the solid phase rate of the shaft portion of the round slab is about 0.5 at the position where the rolling roll consisting of a pair of vertical rolls with an opening angle δ is 90 °. In this state, the round slab is reduced by a pair of vertical rolls, and then the water density is 100 liters / min · m 2 and the cooling zone length by the cooling water sprayed from the spray slab cooling spray nozzle. The steel was forcibly cooled under a condition of 3.0 m to produce a Cr-containing round cast slab for a seamless steel pipe (Example of the present invention).
また、比較のために、圧下ロールでの圧下を行わず、且つ、圧下鋳片冷却用スプレーノズルでの強制冷却も行わない鋳造試験(比較例1)、一対の鞍型ロールで圧下するものの、圧下後に丸鋳片を圧下鋳片冷却用スプレーノズルで強制冷却せずに空気中で放冷する鋳造試験(比較例2)、圧下ロールで圧下せずに圧下鋳片冷却用スプレーノズルで、水量密度100リットル/min・m2及び冷却帯長さ3.0mの条件で強制冷却のみを実施した鋳造試験(比較例3)、及び、一対の鞍型ロールの代わりに一対の平型ロールで丸鋳片を圧下し、その後、圧下鋳片冷却用スプレーノズルで、水量密度100リットル/min・m2及び冷却帯長さ3.0mの条件で強制冷却する鋳造試験(比較例4)も実施した。比較例1〜4では、これら以外のその他の鋳造条件はそれぞれ本発明例と同一とした。 For comparison, a casting test (Comparative Example 1) in which no reduction with a reduction roll and no forced cooling with a reduction slab cooling spray nozzle is performed, although a reduction with a pair of vertical rolls, Casting test (Comparative Example 2) in which the round slab is allowed to cool in the air without being forcedly cooled by the slab cooling spray nozzle after reduction, the amount of water by the slab cooling spray nozzle without being reduced by the reduction roll Casting test (Comparative Example 3) in which only forced cooling was performed under conditions of a density of 100 liters / min · m 2 and a cooling zone length of 3.0 m, and a pair of flat rolls instead of a pair of vertical rolls. A casting test (Comparative Example 4) was also performed in which the slab was crushed and then forcedly cooled with a spray nozzle for cooling the slab slab under conditions of a water density of 100 liters / min · m 2 and a cooling zone length of 3.0 m. . In Comparative Examples 1 to 4, the other casting conditions other than these were the same as those of the inventive examples.
図3に、圧下後の丸鋳片における体積減少率と偏平率εとの関係を、一対の鞍型ロール(以下、「VVロール」と記す)で圧下した場合、つまり本発明例と、一対の平型ロール(以下、「FFロール」と記す)で圧下した場合、つまり比較例4とで比較して示す。図3には、比較例1及び比較例3(「体積減少率=0%」のデータ)の結果も併せて示す。図3からも明らかなように、FFロールで圧下した比較例4に対して、VVロールで圧下した本発明例では、偏平率εの増加が少なく、VVロールで圧下することによりFFロールで圧下した場合に比べて偏平率εは1/3程度となることが分かった。   FIG. 3 shows the relationship between the volume reduction rate and the flatness ratio ε of the round cast slab after being reduced by a pair of vertical rolls (hereinafter referred to as “VV rolls”), that is, the present invention example and a pair When compared with a flat type roll (hereinafter referred to as “FF roll”), that is, compared with Comparative Example 4. FIG. 3 also shows the results of Comparative Example 1 and Comparative Example 3 (data of “volume reduction rate = 0%”). As is clear from FIG. 3, in the example of the present invention in which the reduction was performed with the VV roll, the increase in the flatness ratio ε was small, and the reduction with the FF roll was achieved by the reduction with the VV roll. It has been found that the flatness ratio ε is about 1/3 as compared with the case of the above.
本発明例及び比較例1〜3のなかから、体積減少率が異なる複数本の丸鋳片を選択し、これらの丸鋳片を用いてマンネスマン穿孔試験を行い、マンネスマン穿孔後の素管の内面を調査して、疵の発生状態を調査した。   A plurality of round cast pieces having different volume reduction rates are selected from the examples of the present invention and Comparative Examples 1 to 3, and a Mannesmann drilling test is performed using these round cast pieces. To investigate the state of occurrence of soot.
図4に、比較例1及び比較例2の丸鋳片から製造された素管の内面疵の調査結果を示す。図4において、比較例1は体積減少率=0%のデータである。圧下を行っていない比較例1の疵の発生率は100%であった。これに対して、比較例2においては、0.1%以上3%未満の体積減少率の圧下により、内面疵の発生率は10〜40%程度に低下し、また、体積減少率が3%以上5%未満の圧下により、内面疵の発生率は0〜10%程度に低下した。比較例2において、体積減少率が5%以上の圧下を加えた場合は、疵の発生は認められなかった。従って、比較例2においては、内面疵の発生防止の観点からは、最適範囲は体積減少率が5%以上となるように圧下することであることが分かった。   In FIG. 4, the investigation result of the inner surface flaw of the raw pipe manufactured from the round slab of the comparative example 1 and the comparative example 2 is shown. In FIG. 4, Comparative Example 1 is data of volume reduction rate = 0%. The occurrence rate of wrinkles in Comparative Example 1 in which no reduction was performed was 100%. On the other hand, in Comparative Example 2, due to the reduction of the volume reduction rate of 0.1% or more and less than 3%, the generation rate of inner surface flaws is reduced to about 10 to 40%, and the volume reduction rate is 3%. Due to the above reduction of less than 5%, the occurrence rate of inner surface flaws decreased to about 0 to 10%. In Comparative Example 2, the occurrence of wrinkles was not observed when a reduction in volume reduction rate of 5% or more was applied. Therefore, in Comparative Example 2, it was found that the optimum range was to reduce the volume reduction rate to 5% or more from the viewpoint of preventing the occurrence of internal flaws.
図5に、比較例3及び本発明例の丸鋳片から製造された素管の内面疵の調査結果を示す。図5において、比較例3は体積減少率=0%のデータである。圧下を行っていない比較例3での疵発生率は10〜20%であり、同様に圧下を行っていない比較例1に比べて疵発生率は大幅に減少した。これは、圧下鋳片冷却用スプレーノズルによる強制冷却の効果によるものである。そして、本発明例では、圧下鋳片冷却用スプレーノズルによる強制冷却の効果により、圧下のみを行った比較例2に比べて疵発生率が減少し、体積減少率が2.5%以上となる圧下を加えた場合には、疵発生率は認められなかった。従って、本発明例においては、内面疵の発生防止の観点からは、最適範囲は体積減少率が2.5%以上となるように圧下することであることが分かった。つまり、本発明例を適用することで、比較例2に比べて少ない圧下量で内質に優れた丸鋳片を製造できること、換言すれば、偏平率εを低く抑えたまま内質に優れた丸鋳片を製造できることが分かった。   FIG. 5 shows the results of investigation on the inner surface flaws of the raw pipes manufactured from the round slabs of Comparative Example 3 and Example of the present invention. In FIG. 5, Comparative Example 3 is data of volume reduction rate = 0%. The wrinkle generation rate in Comparative Example 3 in which no reduction was performed was 10 to 20%, and the wrinkle generation rate was significantly reduced as compared to Comparative Example 1 in which similarly no reduction was performed. This is due to the effect of forced cooling by the spray nozzle for cooling the slab. In the example of the present invention, due to the effect of forced cooling by the slab cooling spray nozzle, the rate of occurrence of flaws is reduced as compared with Comparative Example 2 in which only reduction is performed, and the volume reduction rate is 2.5% or more. When reduction was applied, no wrinkle incidence was observed. Therefore, in the example of the present invention, it was found that the optimum range is to reduce the volume reduction rate to 2.5% or more from the viewpoint of preventing the occurrence of inner surface flaws. In other words, by applying the example of the present invention, it is possible to manufacture a round cast slab having excellent inner quality with a reduced amount of reduction compared to Comparative Example 2, in other words, excellent in inner quality while keeping the flat rate ε low. It has been found that round slabs can be produced.
図6は、本発明例の丸鋳片において、丸鋳片の偏平率εと、マンネスマン穿孔時の穿孔性及び素管の偏肉率との関係を示したものである。   FIG. 6 shows the relationship between the flattening ratio ε of the round cast slab, the piercing property at the time of Mannesmann drilling, and the thickness deviation of the raw pipe in the round cast slab of the present invention.
ここで、図6の縦軸に示した穿孔性を示す評点は、穿孔が通常の真円断面の丸鋳片と同じ状態で行えた場合を評点1とし、穿孔中に異音が発生した場合を評点2、更に穿孔中に噛み込み不良が発生した場合を評点3とした。尚、噛み込み不良の状態とは、マンネスマン穿孔が不可能なことではなく、素管の先端部近傍の形状が不良になる部分が著しく長くなる(3m以上)ことに対応している。また、異音が発生する状態とは、形状が不良になる部分が長くなる(1m以上、3m未満)ことに、ほぼ対応する。真円断面の丸鋳片の場合は、形状が不良になる部分の長さは1m未満である。   Here, the score indicating the piercing property shown on the vertical axis of FIG. 6 is a case where the drilling is performed in the same state as a round cast piece having a normal round cross section, and when abnormal noise occurs during drilling. Was rated 2, and a score 3 was assigned when a biting failure occurred during drilling. The state of poor biting does not mean that Mannesmann drilling is not possible, but corresponds to the fact that the shape of the vicinity of the tip of the blank tube becomes extremely long (3 m or more). Moreover, the state where abnormal noise is generated substantially corresponds to the fact that the portion where the shape is defective becomes long (1 m or more and less than 3 m). In the case of a round cast piece having a perfect circular cross section, the length of the portion having a defective shape is less than 1 m.
また、偏肉率は穿孔後の形状不良部分を除いた断面の測定値で評価した。具体的には、真円丸鋳片を用いた場合に発生する偏肉率の3〜4%を基準値とし、これに対して偏肉率の増加が5%未満の場合を評点1、5%以上10%未満を評点2、更に10%以上15%未満を評点3、15%以上を評点4とした。   Further, the uneven thickness ratio was evaluated by a measured value of a cross section excluding a portion having a poor shape after drilling. Specifically, 3 to 4% of the wall thickness ratio generated when a round round slab is used is set as a reference value, and the case where the increase in the wall thickness ratio is less than 5% is rated 1, 5 % Or more and less than 10% was rated 2, and 10% or more and less than 15% was rated 3, and 15% or more was rated 4.
図6に示すように、偏平率εの増加に伴って穿孔性評点及び偏肉率評点は大きくなるが、丸鋳片の偏平率εが3.5%以下の場合には、穿孔性評点及び偏肉率評点ともに真円丸鋳片と同等になることが分かった。   As shown in FIG. 6, as the flatness ratio ε increases, the drillability score and the wall thickness ratio score increase. However, when the flatness ratio ε of the round cast slab is 3.5% or less, the drillability score and It was found that the thickness ratio rating was equivalent to that of a round round slab.
このように、本発明を適用して丸鋳片の体積減少率が2.5%以上で3.5%以下の範囲内で圧下を加えることにより、マンネスマン穿孔による素管に内面疵を発生させることなく、マンネスマン穿孔時の穿孔性及び素管の偏肉率を真円丸鋳片と同等にすることが実現される。これに対して、圧下のみを加えた比較例2では、素管の内面疵を防止するためには、体積減少率が5%以上となる圧下を加える必要があり、そのときの偏平率εは5%程度になり(図3を参照)、マンネスマン穿孔時の穿孔性及び素管の偏肉率は真円丸鋳片の場合に比較して劣化する。   In this way, by applying the present invention and applying a reduction within a range where the volume reduction rate of the round slab is 2.5% or more and 3.5% or less, inner surface flaws are generated in the raw tube by Mannesmann drilling. Therefore, it is possible to make the piercing property and the uneven thickness ratio of the raw tube equal to those of a round round cast slab during Mannesmann drilling. On the other hand, in Comparative Example 2 in which only the reduction was applied, in order to prevent inner surface flaws in the raw tube, it is necessary to apply a reduction in which the volume reduction rate is 5% or more, and the flatness ratio ε at that time is It becomes about 5% (refer to FIG. 3), and the piercing property at the time of Mannesmann drilling and the uneven thickness ratio of the raw tube are deteriorated as compared with the case of a round round slab.
以上に示したように、本発明方法を適用することにより、丸鋳片の内質が向上し、従って、マンネスマン穿孔時の内面疵発生率は大幅に低下し、しかも、偏平率εは大きくならないため、マンネスマン穿孔性の劣化も小さく、また得られた素管の偏肉も低く抑制できることが明らかとなった。   As described above, by applying the method of the present invention, the inner quality of the round cast slab is improved. Therefore, the occurrence rate of inner surface flaws at the time of drilling Mannesmann is greatly reduced, and the flat rate ε does not increase. Therefore, it became clear that the deterioration of Mannesmann's piercing property was small and the uneven thickness of the obtained tube could be suppressed low.
上述の実施例においては、圧下鋳片冷却用スプレーによる丸鋳片の強制冷却条件は、水量密度100リットル/min・m2及び冷却帯長さ3.0mの条件としたが、これに限るものではなく、鋳片表面温度が低下する程度(水量密度10リットル/min・m2以上及び冷却帯長さ1.0m以上)であれば良い。また、上述の実施例では、丸鋳片を圧下した後に圧下鋳片冷却用スプレーにより丸鋳片を強制冷却したが、圧下の直前に丸鋳片を強制冷却しても同様の効果が得られ、また両者を併用しても良い。 In the above-mentioned embodiment, the forced cooling condition of the round slab by the spray for cooling the slab slab is the condition that the water density is 100 liters / min · m 2 and the cooling zone length is 3.0 m. Instead, it is sufficient that the slab surface temperature is lowered (water density of 10 liters / min · m 2 or more and cooling zone length of 1.0 m or more). Further, in the above-described embodiment, the round cast slab was forcibly cooled by the reduction slab cooling spray after the round slab was reduced. However, the same effect can be obtained by forcibly cooling the round slab immediately before the reduction. Moreover, you may use both together.
本発明の実施形態の1例を示す図であり、継目無鋼管用丸鋳片を連続鋳造により製造する状況を示す概略図である。It is a figure which shows one example of embodiment of this invention, and is the schematic which shows the condition which manufactures the round cast piece for seamless steel pipes by continuous casting. 図1に示す圧下ロールを用いて鋳造中の丸鋳片を圧下している状態を示す斜視図である。It is a perspective view which shows the state which is rolling down the round slab in casting using the rolling roll shown in FIG. 圧下後の丸鋳片における体積減少率と偏平率εとの関係を示す図である。It is a figure which shows the relationship between the volume reduction rate and flatness ratio (epsilon) in the round cast slab after reduction. 比較例1及び比較例2の丸鋳片から製造された素管の内面疵の調査結果を示す図である。It is a figure which shows the investigation result of the internal surface flaw of the raw pipe manufactured from the round cast of the comparative example 1 and the comparative example 2. 比較例3及び本発明例の丸鋳片から製造された素管の内面疵の調査結果を示す図である。It is a figure which shows the investigation result of the internal surface flaw of the raw pipe manufactured from the round cast of the comparative example 3 and the example of this invention. 本発明例の丸鋳片において、丸鋳片の偏平率εと、マンネスマン穿孔時の穿孔性及び素管の偏肉率との関係を示した図である。In the round slab of the example of the present invention, it is a diagram showing the relationship between the flattening ratio ε of the round slab, the piercing property at the time of drilling Mannesmann, and the wall thickness ratio of the raw pipe. 溶鋼中のCr濃度と溶鋼の粘度との関係を示した図である。It is the figure which showed the relationship between Cr density | concentration in molten steel, and the viscosity of molten steel. 溶鋼中のCr濃度と溶鋼の粘度との関係を示した図である。It is the figure which showed the relationship between Cr density | concentration in molten steel, and the viscosity of molten steel.
符号の説明Explanation of symbols
1 円形鋳型
2 ガイドロール
3 ピンチロール
4 電磁攪拌装置
5 圧下ロール
6 圧下鋳片冷却用スプレーノズル
6’ 圧下直前鋳片冷却用スプレーノズル
7 鋳片切断機
8 丸鋳片
9 未凝固溶鋼層
10 凝固シェル
11 鞍型ロール
DESCRIPTION OF SYMBOLS 1 Circular mold 2 Guide roll 3 Pinch roll 4 Electromagnetic stirrer 5 Rolling roll 6 Spray nozzle for cooling slab slab 6 'Spray nozzle for cooling slab immediately before squeezing 7 Cast slab cutting machine 8 Round cast 9 Unsolidified molten steel layer 10 Solidification Shell 11 vertical roll

Claims (2)

  1. 円形鋳型による連続鋳造中の丸鋳片に、該丸鋳片の軸芯部の固相率が0.3以上1.0以下の状態のときに、該丸鋳片の凝固完了点近傍に設置した一対の鞍型ロールにより圧下を加え、該圧下の後に、水量密度が10リットル/min・m 2 以上で冷却帯長さが1.0m以上の条件で、連続鋳造中の丸鋳片を強制冷却することを特徴とする、継目無鋼管用丸鋳片の連続鋳造方法。 Installed in the vicinity of the solidification completion point of the round cast slab when the solid phase ratio of the core part of the round cast slab is 0.3 or more and 1.0 or less. the reduction applied by a pair of saddle-type rolls, after the piezoelectric under in water density is more than 1.0m cooling zone length at 10 l / min · m 2 or more conditions, the round billet in continuous casting A method for continuously casting round slabs for seamless steel pipes, characterized by forced cooling.
  2. 前記丸鋳片の体積減少率が2.5%以上で3.5%以下の範囲内となる条件で圧下を加えることを特徴とする、請求項1に記載の継目無鋼管用丸鋳片の連続鋳造方法。2. The round slab for seamless steel pipes according to claim 1, wherein the rolling reduction is applied under a condition that a volume reduction rate of the round slab is in a range of 2.5% to 3.5%. Continuous casting method.
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