JP6402750B2 - Steel continuous casting method - Google Patents
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- JP6402750B2 JP6402750B2 JP2016148204A JP2016148204A JP6402750B2 JP 6402750 B2 JP6402750 B2 JP 6402750B2 JP 2016148204 A JP2016148204 A JP 2016148204A JP 2016148204 A JP2016148204 A JP 2016148204A JP 6402750 B2 JP6402750 B2 JP 6402750B2
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- 238000009749 continuous casting Methods 0.000 title claims description 60
- 229910000831 Steel Inorganic materials 0.000 title claims description 34
- 239000010959 steel Substances 0.000 title claims description 34
- 238000000034 method Methods 0.000 title claims description 31
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 107
- 229910052802 copper Inorganic materials 0.000 claims description 107
- 239000010949 copper Substances 0.000 claims description 107
- 239000000126 substance Substances 0.000 claims description 75
- 230000004907 flux Effects 0.000 claims description 71
- 238000007711 solidification Methods 0.000 claims description 59
- 230000008023 solidification Effects 0.000 claims description 59
- 230000005499 meniscus Effects 0.000 claims description 52
- 239000000463 material Substances 0.000 claims description 47
- 239000000498 cooling water Substances 0.000 claims description 37
- 229910052751 metal Inorganic materials 0.000 claims description 29
- 239000002184 metal Substances 0.000 claims description 29
- 229910000881 Cu alloy Inorganic materials 0.000 claims description 27
- 238000007747 plating Methods 0.000 claims description 24
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 claims description 23
- 229910052755 nonmetal Inorganic materials 0.000 claims description 20
- 230000007423 decrease Effects 0.000 claims description 13
- 238000009826 distribution Methods 0.000 claims description 12
- 229910052759 nickel Inorganic materials 0.000 claims description 11
- 229910045601 alloy Inorganic materials 0.000 claims description 8
- 239000000956 alloy Substances 0.000 claims description 8
- 238000005266 casting Methods 0.000 description 31
- 230000035882 stress Effects 0.000 description 28
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 16
- 238000001816 cooling Methods 0.000 description 14
- 238000005336 cracking Methods 0.000 description 14
- 230000000694 effects Effects 0.000 description 13
- 230000009466 transformation Effects 0.000 description 10
- 229910000954 Medium-carbon steel Inorganic materials 0.000 description 8
- 229910052742 iron Inorganic materials 0.000 description 8
- 239000011651 chromium Substances 0.000 description 6
- 230000000052 comparative effect Effects 0.000 description 5
- 238000009434 installation Methods 0.000 description 5
- 239000000843 powder Substances 0.000 description 5
- 238000010583 slow cooling Methods 0.000 description 5
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 5
- 229910052804 chromium Inorganic materials 0.000 description 4
- 239000007921 spray Substances 0.000 description 4
- 230000008646 thermal stress Effects 0.000 description 4
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 3
- 229910052799 carbon Inorganic materials 0.000 description 3
- 239000000919 ceramic Substances 0.000 description 3
- 239000012141 concentrate Substances 0.000 description 3
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- 238000007751 thermal spraying Methods 0.000 description 3
- 238000012546 transfer Methods 0.000 description 3
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 2
- 229910017709 Ni Co Inorganic materials 0.000 description 2
- 229910003267 Ni-Co Inorganic materials 0.000 description 2
- 229910003262 Ni‐Co Inorganic materials 0.000 description 2
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- 229910000531 Co alloy Inorganic materials 0.000 description 1
- 229910000570 Cupronickel Inorganic materials 0.000 description 1
- MBMLMWLHJBBADN-UHFFFAOYSA-N Ferrous sulfide Chemical compound [Fe]=S MBMLMWLHJBBADN-UHFFFAOYSA-N 0.000 description 1
- 102000005298 Iron-Sulfur Proteins Human genes 0.000 description 1
- 108010081409 Iron-Sulfur Proteins Proteins 0.000 description 1
- 229910018487 Ni—Cr Inorganic materials 0.000 description 1
- 206010037660 Pyrexia Diseases 0.000 description 1
- 229910000796 S alloy Inorganic materials 0.000 description 1
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
- QXZUUHYBWMWJHK-UHFFFAOYSA-N [Co].[Ni] Chemical compound [Co].[Ni] QXZUUHYBWMWJHK-UHFFFAOYSA-N 0.000 description 1
- 229910001566 austenite Inorganic materials 0.000 description 1
- 238000005452 bending Methods 0.000 description 1
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- 229910052748 manganese Inorganic materials 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 229910000623 nickel–chromium alloy Inorganic materials 0.000 description 1
- 230000010355 oscillation Effects 0.000 description 1
- 230000002085 persistent effect Effects 0.000 description 1
- 229910052698 phosphorus Inorganic materials 0.000 description 1
- 230000000644 propagated effect Effects 0.000 description 1
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- 238000005096 rolling process Methods 0.000 description 1
- VSZWPYCFIRKVQL-UHFFFAOYSA-N selanylidenegallium;selenium Chemical compound [Se].[Se]=[Ga].[Se]=[Ga] VSZWPYCFIRKVQL-UHFFFAOYSA-N 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 238000005507 spraying Methods 0.000 description 1
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- 229910052717 sulfur Inorganic materials 0.000 description 1
- 239000011593 sulfur Substances 0.000 description 1
- 229910000859 α-Fe Inorganic materials 0.000 description 1
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- Continuous Casting (AREA)
Description
本発明は、鋳型内での凝固シェルの不均一冷却に起因する鋳片表面割れを抑制して溶鋼を連続鋳造する連続鋳造方法に関する。 The present invention relates to a continuous casting method in which molten steel is continuously cast while suppressing slab surface cracking caused by uneven cooling of a solidified shell in a mold.
鋼の連続鋳造では、鋳型内に注入された溶鋼は水冷式鋳型によって冷却され、鋳型との接触面で溶鋼が凝固して凝固層（「凝固シェル」という）が生成される。この凝固シェルを外殻とし、内部を未凝固層とする鋳片は、鋳型下流側に設置された水スプレーや気水スプレーによって冷却されながら鋳型下方に連続的に引き抜かれる。鋳片は、水スプレーや気水スプレーによる冷却によって中心部まで凝固し、その後、ガス切断機などによって切断されて、所定長さの鋳片が製造されている。 In continuous casting of steel, molten steel poured into a mold is cooled by a water-cooled mold, and the molten steel is solidified at a contact surface with the mold to generate a solidified layer (referred to as “solidified shell”). The slab having the solidified shell as an outer shell and the inside as an unsolidified layer is continuously drawn below the mold while being cooled by a water spray or an air / water spray installed on the downstream side of the mold. The slab is solidified to the center by cooling with water spray or air-water spray, and then cut by a gas cutter or the like to produce a slab of a predetermined length.
鋳型内における冷却が不均一になると、凝固シェルの厚みが鋳片の鋳造方向及び鋳型幅方向で不均一となる。凝固シェルには、凝固シェルの収縮や変形に起因する応力が作用し、凝固初期においては、この応力が凝固シェルの薄肉部に集中し、この応力によって凝固シェルの表面に割れが発生する。この割れは、その後の熱応力や連続鋳造機のロールによる曲げ応力及び矯正応力などの外力により拡大し、大きな表面割れとなる。凝固シェル厚みの不均一度が大きい場合には、鋳型内での縦割れとなり、この縦割れから溶鋼が流出するブレークアウトが発生する場合もある。鋳片に存在する割れは、次工程の圧延工程で表面欠陥となることから、鋳造後の鋳片の段階において、鋳片の表面を手入れして表面割れを除去することが必要となる。 If the cooling in the mold becomes non-uniform, the thickness of the solidified shell becomes non-uniform in the casting direction of the slab and in the mold width direction. A stress caused by the shrinkage or deformation of the solidified shell acts on the solidified shell, and in the initial stage of solidification, this stress is concentrated on the thin portion of the solidified shell, and the stress causes cracks on the surface of the solidified shell. This crack expands due to subsequent external stresses such as thermal stress, bending stress due to the roll of a continuous casting machine, and straightening stress, resulting in a large surface crack. When the non-uniformity of the solidified shell thickness is large, a vertical crack is generated in the mold, and a breakout in which the molten steel flows out from the vertical crack may occur. Since the cracks present in the slab become surface defects in the subsequent rolling process, it is necessary to care for the surface of the slab and remove the surface cracks at the stage of the cast slab after casting.
鋳型内の不均一凝固は、特に、炭素含有量が０．０８〜０．１７質量％の鋼（中炭素鋼という）で発生しやすい。炭素含有量が０．０８〜０．１７質量％の鋼では、凝固時に包晶反応が起こり、鋳型内の不均一凝固は、この包晶反応によるδ鉄（フェライト）からγ鉄（オーステナイト）への変態時の体積収縮による変態応力に起因すると考えられている。つまり、この変態応力に起因する歪みによって凝固シェルが変形し、この変形によって凝固シェルが鋳型内壁面から離れる。鋳型内壁面から離れた部位は鋳型による冷却が低下し、この鋳型内壁面から離れた部位（この鋳型内壁面から離れた部位を「デプレッション」という）の凝固シェル厚みが薄くなり、凝固シェル厚みが薄くなることで、この部分に上記応力が集中し、表面割れが発生すると考えられている。 Inhomogeneous solidification in the mold is likely to occur particularly in steel (referred to as medium carbon steel) having a carbon content of 0.08 to 0.17% by mass. In a steel having a carbon content of 0.08 to 0.17% by mass, a peritectic reaction occurs during solidification, and the non-uniform solidification in the mold is caused by the peritectic reaction from δ iron (ferrite) to γ iron (austenite). It is thought to be caused by transformation stress due to volume shrinkage during transformation. That is, the solidified shell is deformed by the strain caused by the transformation stress, and the solidified shell is separated from the inner wall surface of the mold by this deformation. Cooling by the mold is reduced at the part away from the inner wall surface of the mold, and the solidified shell thickness of the part away from the inner wall surface of the mold (the part away from the inner wall surface of the mold is referred to as “depression”) is reduced. It is considered that the above stress concentrates on this portion and the surface crack occurs due to the thinning.
特に、鋳片引き抜き速度を増加した場合には、凝固シェルから鋳型冷却水への平均熱流束が増加する（凝固シェルが急速冷却される）のみならず、熱流束の分布が不規則で且つ不均一になることから、鋳片表面割れの発生が増加傾向となる。具体的には、鋳片厚みが２００ｍｍ以上のスラブ連続鋳造機においては、鋳片引き抜き速度が１．５ｍ／ｍｉｎ以上になると表面割れが発生しやすくなる。 In particular, when the slab drawing speed is increased, the average heat flux from the solidified shell to the mold cooling water increases (the solidified shell is rapidly cooled), and the heat flux distribution is irregular and irregular. Since it becomes uniform, the occurrence of slab surface cracks tends to increase. Specifically, in a slab continuous casting machine having a slab thickness of 200 mm or more, surface cracks are likely to occur when the slab drawing speed is 1.5 m / min or more.
そこで、従来、上記の包晶反応を伴う、表面割れが発生しやすい鋼種の表面割れ（特に縦割れ）を抑制するために、種々の手段が提案されている。 Therefore, conventionally, various means have been proposed in order to suppress surface cracks (particularly longitudinal cracks) of the steel types that are likely to cause surface cracks that accompany the peritectic reaction.
例えば、特許文献１には、結晶化しやすい組成のモールドパウダーを使用し、モールドパウダー層の熱抵抗を増大させて凝固シェルを緩冷却することが提案されている。これは、緩冷却によって凝固シェルに作用する応力を低下させて表面割れを抑制するという技術である。しかしながら、モールドパウダーによる緩冷却効果のみでは、不均一凝固を十分に改善するまでには至っておらず、特に凝固に伴う僅かな温度低下で変態が生じる中炭素鋼では、表面割れの発生を防止することはできないのが実情である。 For example, Patent Document 1 proposes using mold powder having a composition that is easily crystallized, and increasing the thermal resistance of the mold powder layer to slowly cool the solidified shell. This is a technique of suppressing surface cracking by reducing the stress acting on the solidified shell by slow cooling. However, only the slow cooling effect by the mold powder has not sufficiently improved the non-uniform solidification, especially in medium carbon steel where transformation occurs due to a slight temperature drop accompanying solidification, preventing the occurrence of surface cracks. The fact is that you can't.
特許文献２には、鋳型内壁面に縦溝と横溝とを設け、これら縦溝及び横溝の内部にモールドパウダーを流入させ、これにより、鋳型の冷却を緩冷却化すると同時に鋳型幅方向で均一化し、鋳片の縦割れを防止する技術が提案されている。しかしながら、鋳片との接触によって鋳型内壁面は摩耗し、鋳型内壁面に設けた溝が浅くなると、モールドパウダーの流れ込み量が少なくなって緩冷却効果が低減するという問題、つまり、緩冷却効果が持続しないという問題がある。また、鋳造開始時の空の鋳型空間内への溶鋼注入時に、注入した溶鋼が鋳型内壁面に設けた溝の内部に侵入して凝固し、鋳型銅板と凝固シェルとが固着して、凝固シェルの引き抜きができなくなり、拘束性ブレークアウトが発生する虞があるという問題もある。 In Patent Document 2, a vertical groove and a horizontal groove are provided on the inner wall surface of the mold, and mold powder is allowed to flow into the vertical groove and the horizontal groove, thereby slowing down the cooling of the mold and at the same time uniforming in the mold width direction. A technique for preventing vertical cracking of a slab has been proposed. However, when the inner wall surface of the mold is worn due to contact with the slab, and the groove provided on the inner wall surface of the mold becomes shallow, the amount of mold powder flowing in decreases and the slow cooling effect is reduced. There is a problem of not persisting. In addition, when molten steel is poured into an empty mold space at the start of casting, the injected molten steel penetrates into the groove provided on the inner wall surface of the mold and solidifies, and the mold copper plate and the solidified shell adhere to each other, thereby solidifying the shell. There is also a problem in that it becomes impossible to pull out the wire and a constraining breakout may occur.
特許文献３には、鋳型内壁面に格子状の溝を設けた鋳型、及び、前記格子状の溝に異種金属（Ｎｉ，Ｃｒ）またはセラミックス（ＢＮ、ＡｌＮ、ＺｒＯ２）を充填した鋳型が提案されている。この技術は、溝部と溝部以外の部分とで抜熱量に差を生じさせ、凝固に伴う変態や熱収縮による応力を低抜熱の領域に分散させることで、鋳片の縦割れを抑制するという技術である。しかしながら、溝が格子状であり、格子溝形状では、鋳型内壁面の溝部と鋳型銅板（銅または銅合金）との境界が直線であり、熱膨張差に起因して境界面に割れが発生し且つ伝播しやすく、鋳型寿命が低下するという問題がある。 Patent Document 3 proposes a mold in which a lattice-shaped groove is provided on the inner wall surface of the mold, and a mold in which the lattice-shaped groove is filled with a different metal (Ni, Cr) or ceramics (BN, AlN, ZrO 2 ). Has been. This technology creates a difference in the amount of heat removal between the groove and the portion other than the groove, and suppresses vertical cracking of the slab by dispersing the stress due to transformation and thermal shrinkage accompanying solidification in the low heat removal region. Technology. However, the grooves are in a lattice shape, and in the lattice groove shape, the boundary between the groove portion of the inner wall surface of the mold and the mold copper plate (copper or copper alloy) is a straight line, and the boundary surface is cracked due to the difference in thermal expansion. In addition, there is a problem that propagation is easy and the mold life is reduced.
特許文献４には、鋳型内壁面に鋳造方向と平行な縦溝を設けた鋳型、及び、前記縦溝に異種金属（Ｎｉ，Ｃｒ）またはセラミックス（ＢＮ、ＡｌＮ、ＺｒＯ２）を充填した鋳型を用い、鋳片引き抜き速度と鋳型振動周期とを所定の範囲に規定する連続鋳造方法が提案されている。特許文献４によれば、鋳片引き抜き速度に応じて鋳型振動周期を適正化することで、鋳片に形成されるオシレーションマークが横溝を付与したように働き、縦溝のみでも、特許文献３と同様の表面割れ低減効果が認められるとしている。しかしながら、特許文献３と同様に、鋳型内壁面の溝部と鋳型銅板（銅または銅合金）との境界が直線であり、熱膨張差に起因して境界面に割れが発生し且つ伝播しやすく、鋳型寿命が低下するという問題がある。 Patent Document 4 discloses a mold in which a vertical groove parallel to the casting direction is provided on the inner wall surface of the mold, and a mold in which the vertical groove is filled with a different metal (Ni, Cr) or ceramics (BN, AlN, ZrO 2 ). There has been proposed a continuous casting method that uses a slab drawing speed and a mold vibration cycle within a predetermined range. According to Patent Document 4, by optimizing the mold vibration period in accordance with the slab drawing speed, the oscillation mark formed on the slab works as if a lateral groove was provided. It is said that the same effect of reducing surface cracks is observed. However, as in Patent Document 3, the boundary between the groove on the inner wall surface of the mold and the mold copper plate (copper or copper alloy) is a straight line, and the boundary surface is easily cracked and propagated due to the difference in thermal expansion. There is a problem that the mold life is reduced.
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、鋳造開始時での拘束性ブレークアウトの発生及び鋳型銅板表面の割れによる鋳型寿命低下を起こすことなく、凝固初期の凝固シェルの不均一冷却による表面割れ、及び、包晶反応を伴う中炭素鋼でのδ鉄からγ鉄への変態に起因する凝固シェル厚みの不均一による表面割れを長期間に亘って抑制できる鋼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 to generate a constraining breakout at the start of casting and to reduce the mold life due to cracks on the surface of the mold copper plate without causing any initial solidification. Surface cracks due to non-uniform cooling of solidified shells and surface cracks due to non-uniform solidified shell thickness due to transformation from δ iron to γ iron in medium carbon steel with peritectic reaction can be suppressed over a long period of time. It is to provide a method for continuous casting of steel.
上記課題を解決するための本発明の要旨は以下のとおりである。
［１］少なくともメニスカスからメニスカスの下方３００ｍｍの位置までの領域の銅合金製鋳型銅板の内壁面の一部分または全体に、鋳型銅板の熱伝導率とは異なる熱伝導率の金属または非金属が充填された複数個の異種物質充填部を有する水冷式銅合金製鋳型を用い、タンディッシュ内の溶鋼を前記鋳型内に注入して連続鋳造する鋼の連続鋳造方法であって、前記異種物質充填部を配置した領域であって、前記メニスカスの下方５０ｍｍ位置における鋳型銅板と鋳型冷却水との間の熱流束の鋳型幅方向の平均値が、鋳片引き抜き速度に応じて定まる下記の（１）式を満足する範囲であり、且つ、前記メニスカスの下方５０ｍｍ位置における鋳型銅板と鋳型冷却水との間の熱流束の鋳型幅方向の標準偏差が、下記の（２）式を満足する範囲であることを特徴とする、鋼の連続鋳造方法。
０．５０×Ｖｃ＋０．５５≦Ｑ≦１．２０×Ｖｃ＋０．７５・・・（１）
σ（Ｑ）≦０．２０・・・（２）
但し、（１）式において、Ｖｃは鋳片引き抜き速度（ｍ／ｍｉｎ）、Ｑは鋳型銅板と鋳型冷却水との間の熱流束の鋳型幅方向の平均値（ＭＷ／ｍ２）であり、また、（２）式において、σ（Ｑ）は鋳型銅板と鋳型冷却水との間の熱流束の鋳型幅方向の標準偏差（ＭＷ／ｍ２）である。
［２］前記複数個の異種物質充填部は、前記内壁面に周期的に増減する熱抵抗分布または熱流束分布を形成することを特徴とする、［１］に記載の鋼の連続鋳造方法。
［３］前記複数個の異種物質充填部は、前記内壁面に設けられた円形凹溝または擬似円形凹溝の内部に前記金属または非金属が充填されて形成されることを特徴とする、［１］または［２］に記載の鋼の連続鋳造方法。
［４］前記複数個の異種物質充填部は、互いに独立して配置されることを特徴とする、［１］から［３］の何れか１つに記載の鋼の連続鋳造方法。
［５］前記異種物質充填部が配置された領域を通過するときの凝固シェルの凝固係数と、前記異種物質充填部が配置されていない領域を通過するときの凝固シェルの凝固係数とが、下記の（３）式または（４）式を満足することを特徴とする、［１］から［４］の何れか１つに記載の鋼の連続鋳造方法。
０．６≦Ｋ（Ｃ）／Ｋ（Ｏ）≦０．９５（但し、Ｋ（Ｃ）＜Ｋ（Ｏ）の場合）・・・（３）
０．６≦Ｋ（Ｏ）／Ｋ（Ｃ）≦０．９５（但し、Ｋ（Ｃ）＞Ｋ（Ｏ）の場合）・・・（４）
但し、（３）式及び（４）式において、Ｋ（Ｃ）は、異種物質充填部が配置された領域を通過するときの凝固シェルの凝固係数（ｍｍ／ｍｉｎ０．５）、Ｋ（Ｏ）は、異種物質充填部が配置されていない領域を通過するときの凝固シェルの凝固係数（ｍｍ／ｍｉｎ０．５）である。
［６］前記内壁面には、厚みが０．１ｍｍ以上３．０ｍｍ以下のニッケルまたはニッケルを含有する合金の鍍金層が形成されており、前記異種物質充填部は前記鍍金層で覆われていることを特徴とする、［１］から［５］の何れか１つに記載の鋼の連続鋳造方法。
The gist of the present invention for solving the above problems is as follows.
[1] At least a part or the whole inner wall surface of the copper alloy mold copper plate in the region from the meniscus to a position 300 mm below the meniscus is filled with a metal or a nonmetal having a thermal conductivity different from the thermal conductivity of the mold copper plate. A continuous casting method of steel in which molten steel in a tundish is poured into the mold and continuously cast using a water-cooled copper alloy mold having a plurality of different substance filling parts, The following formula (1) in which the average value in the mold width direction of the heat flux between the mold copper plate and the mold cooling water at the position 50 mm below the meniscus is determined according to the slab drawing speed. The standard deviation in the mold width direction of the heat flux between the mold copper plate and the mold cooling water at the position 50 mm below the meniscus is a range that satisfies the following formula (2). Characterized Rukoto, continuous casting method of steel.
0.50 × V c + 0.55 ≦ Q ≦ 1.20 × V c +0.75 (1)
σ (Q) ≦ 0.20 (2)
However, in the formula (1), V c is the slab drawing speed (m / min), and Q is the average value (MW / m 2 ) of the heat flux between the mold copper plate and the mold cooling water in the mold width direction. In the equation (2), σ (Q) is a standard deviation (MW / m 2 ) in the mold width direction of the heat flux between the mold copper plate and the mold cooling water.
[2] The continuous casting method for steel according to [1], wherein the plurality of different-material filling portions form a thermal resistance distribution or a heat flux distribution that periodically increases and decreases on the inner wall surface.
[3] The plurality of different substance filling portions are formed by filling the metal or non-metal into a circular concave groove or a pseudo circular concave groove provided on the inner wall surface. The continuous casting method of steel according to [1] or [2].
[4] The continuous casting method for steel according to any one of [1] to [3], wherein the plurality of different-material filling portions are arranged independently of each other.
[5] The solidification coefficient of the solidified shell when passing through the region where the foreign substance filling portion is disposed and the solidification coefficient of the solidified shell when passing through the region where the foreign material filling portion is not disposed are as follows: The method of continuous casting of steel according to any one of [1] to [4], wherein the formula (3) or (4) is satisfied.
0.6 ≦ K (C) / K (O) ≦ 0.95 (provided that K (C) <K (O)) (3)
0.6 ≦ K (O) / K (C) ≦ 0.95 (provided that K (C)> K (O)) (4)
However, in the formulas (3) and (4), K (C) is the solidification coefficient (mm / min 0.5 ) of the solidified shell when passing through the region where the dissimilar substance filling portion is arranged, K (O ) Is a solidification coefficient (mm / min 0.5 ) of the solidified shell when passing through a region where the different substance filling portion is not disposed.
[6] On the inner wall surface, a plating layer of nickel or an alloy containing nickel having a thickness of 0.1 mm or more and 3.0 mm or less is formed, and the dissimilar substance filling portion is covered with the plating layer. The continuous casting method for steel according to any one of [1] to [5], characterized in that:
本発明によれば、複数個の異種物質充填部を、少なくともメニスカスからメニスカスの下方３００ｍｍの位置までの範囲に有する連続鋳造用鋳型を用い、メニスカスの下方５０ｍｍ位置における鋳型銅板と鋳型冷却水との間の熱流束の鋳型幅方向の平均値、及び、メニスカスの下方５０ｍｍ位置における鋳型銅板と鋳型冷却水との間の熱流束の鋳型幅方向の標準偏差を所定の値に制御するので、メニスカス近傍の鋳型幅方向及び鋳造方向における連続鋳造用鋳型の熱抵抗が、その値を所定の範囲内として、周期的に増減し、これによって、メニスカス近傍、つまり、凝固初期での凝固シェルから連続鋳造用鋳型への熱流束が周期的に増減する。この熱流束の周期的な増減により、δ鉄からγ鉄への変態による応力や熱応力が低減し、これらの応力によって生じる凝固シェルの変形が小さくなり、凝固シェルの変形が小さくなることで、凝固シェルの変形に起因する不均一な熱流束分布が均一化され、且つ、発生する応力が分散されて個々の歪量が小さくなる。その結果、凝固シェル表面における割れの発生が抑制される。 According to the present invention, a continuous casting mold having at least a plurality of different substance filling portions in a range from the meniscus to a position 300 mm below the meniscus is used, and the mold copper plate and the mold cooling water at the position 50 mm below the meniscus are used. Since the average value of the heat flux between the molds in the mold width direction and the standard deviation in the mold width direction of the heat flux between the mold copper plate and the mold cooling water at the position 50 mm below the meniscus is controlled to a predetermined value, the vicinity of the meniscus The thermal resistance of the continuous casting mold in the mold width direction and the casting direction of the mold is periodically increased or decreased within the predetermined range, thereby allowing continuous casting from the solidified shell in the vicinity of the meniscus, that is, in the initial stage of solidification. The heat flux to the mold increases and decreases periodically. By periodically increasing and decreasing the heat flux, the stress and thermal stress due to transformation from δ iron to γ iron are reduced, the deformation of the solidified shell caused by these stresses is reduced, and the deformation of the solidified shell is reduced, The non-uniform heat flux distribution due to the deformation of the solidified shell is made uniform, and the generated stress is dispersed to reduce the amount of individual strain. As a result, the occurrence of cracks on the surface of the solidified shell is suppressed.
以下、発明の実施の形態を通じて本発明を具体的に説明する。図１は、本実施形態に係る連続鋳造方法で使用する連続鋳造用鋳型の一部を構成する鋳型長辺銅板であって、内壁面側に異種物質充填部が形成された鋳型長辺銅板を内壁面側から見た概略側面図である。また、図２は、図１に示す鋳型長辺銅板のＸ−Ｘ’断面図である。 Hereinafter, the present invention will be specifically described through embodiments of the invention. FIG. 1 shows a mold long side copper plate constituting a part of a continuous casting mold used in the continuous casting method according to the present embodiment. It is the schematic side view seen from the inner wall surface side. FIG. 2 is a cross-sectional view taken along the line X-X ′ of the long side copper plate shown in FIG. 1.
図１に示す連続鋳造用鋳型は、スラブ鋳片を鋳造するための連続鋳造用鋳型の一例である。スラブ鋳片用の連続鋳造用鋳型は、一対の銅合金製の鋳型長辺銅板と一対の銅合金製の鋳型短辺銅板とを組み合わせて構成され、図１は、そのうちの鋳型長辺銅板１を示している。鋳型短辺銅板も鋳型長辺銅板１と同様に、その内壁面側に異種物質充填部３が形成されるとして、ここでは、鋳型短辺銅板についての説明は省略する。但し、スラブ鋳片においては、スラブ厚みに対してスラブ幅が極めて大きいという形状に起因して、鋳片長辺面側の凝固シェルで応力集中が起こりやすく、鋳片長辺面側で表面割れが発生しやすい。したがって、スラブ鋳片用の連続鋳造用鋳型の鋳型短辺銅板には、異種物質充填部を設置しなくてもよい。 The continuous casting mold shown in FIG. 1 is an example of a continuous casting mold for casting a slab slab. A continuous casting mold for a slab slab is configured by combining a pair of copper alloy long mold copper plates and a pair of copper alloy short mold copper plates, and FIG. Is shown. Similarly to the long-side copper plate 1, the short-side copper plate is formed with the different material filling portion 3 on the inner wall surface side, and the description of the short-side copper plate is omitted here. However, in slab slabs, stress concentration is likely to occur in the solidified shell on the long side of the slab due to the shape of the slab width being extremely large relative to the slab thickness, and surface cracks occur on the long side of the slab It's easy to do. Therefore, the dissimilar substance filling part does not have to be installed on the short side copper plate of the continuous casting mold for the slab slab.
図１に示すように、鋳型長辺銅板１における定常鋳造時のメニスカスの位置よりも長さＱ（長さＱは、ゼロ以上の任意の値）離れた上方の位置から、メニスカスよりも長さＬだけ下方の位置までの鋳型長辺銅板１の内壁面には、直径をｄとし、鋳型長辺銅板１の熱伝導率とは異なる熱伝導率の金属または非金属が充填された、複数個の異種物質充填部３が、異種物質充填部同士の間隔をＰとして設置されている。ここで、「メニスカス」とは「鋳型内溶鋼湯面」であり、非鋳造中にはその位置は明確でないが、通常の鋼の連続鋳造操業では、メニスカス位置を鋳型銅板の上端から５０ｍｍないし２００ｍｍ程度下方の位置としている。したがって、メニスカス位置が鋳型長辺銅板１の上端から５０ｍｍ下方の位置であっても、また、上端から２００ｍｍ下方の位置であっても、長さＱ及び長さＬが、以下に説明する条件を満足するように、異種物質充填部３を配置すればよい。 As shown in FIG. 1, the length is longer than the meniscus from a position above the length Q (length Q is an arbitrary value of zero or more) away from the position of the meniscus at the time of steady casting in the long copper plate 1 of the mold. The inner wall surface of the mold long side copper plate 1 up to a position below L is filled with a metal or a nonmetal having a diameter d and a thermal conductivity different from that of the mold long side copper plate 1. The dissimilar substance filling part 3 is installed with P being the interval between the different substance filling parts. Here, “meniscus” is “molten steel surface in mold”, and its position is not clear during non-casting, but in the normal continuous casting operation of steel, the meniscus position is 50 mm to 200 mm from the upper end of the mold copper plate. The position is about below. Therefore, even if the meniscus position is 50 mm below the upper end of the long copper plate 1 and 200 mm below the upper end, the length Q and the length L satisfy the conditions described below. What is necessary is just to arrange | position the dissimilar substance filling part 3 so that it may be satisfied.
即ち、凝固シェルの初期凝固への影響を勘案すれば、異種物質充填部３の設置領域は、少なくとも、メニスカスからメニスカスの下方３００ｍｍの位置までの領域とする必要があり、したがって、長さＬは、３００ｍｍ以上とする必要がある。長さＬを少なくとも３００ｍｍ確保することで、鋳片引き抜き速度を、現在のスラブ連続鋳造機の最高速度以上である４．０ｍ／ｍｉｎと仮定しても、凝固シェルは、凝固開始後４．５秒の期間は異種物質充填部３の設置領域に滞在し、異種物質充填部３による熱流束の繰り返し変動、より好ましくは周期的な変動の効果が十分に得られ、表面割れの発生しやすい高速鋳造時や中炭素鋼の鋳造時でも、鋳片表面割れの抑制効果が得られる。尚、長さＬに上限はなく、鋳型下端まで異種物質充填部３を設置してもよい。 That is, in consideration of the influence on the initial solidification of the solidified shell, the installation region of the foreign substance filling portion 3 needs to be at least a region from the meniscus to a position 300 mm below the meniscus, and therefore the length L is , 300 mm or more is necessary. By securing a length L of at least 300 mm, the solidified shell is 4.5 mm after the start of solidification even if the slab drawing speed is assumed to be 4.0 m / min, which is higher than the maximum speed of the current slab continuous casting machine. During the period of seconds, it stays in the installation area of the foreign substance filling part 3 and the effect of repeated fluctuations of the heat flux by the foreign substance filling part 3, more preferably periodic fluctuations, can be sufficiently obtained, and high speed is likely to cause surface cracks. Even at the time of casting or at the time of casting of medium carbon steel, the effect of suppressing slab surface cracking can be obtained. In addition, there is no upper limit in the length L, and the foreign substance filling part 3 may be installed up to the lower end of the mold.
一方、異種物質充填部３の上端部の位置は、メニスカスと同一位置またはメニスカス位置よりも上方である限りどこの位置でもよく、従って、図１に示す長さＱは、ゼロ以上の任意の値としてよい。但し、メニスカスは、鋳造中に異種物質充填部３の設置領域に存在する必要があり、しかも、メニスカスは鋳造中に上下方向に変動するので、異種物質充填部３の上端部が常にメニスカスよりも上方位置となるように、異種物質充填部３の上端部をメニスカスよりも１０ｍｍ程度上方位置とすることが好ましく、異種物質充填部３の上端部をメニスカスよりも２０ｍｍ〜５０ｍｍ程度上方位置とすることがより好ましい。 On the other hand, the position of the upper end portion of the different substance filling portion 3 may be any position as long as it is the same position as the meniscus or above the meniscus position. Therefore, the length Q shown in FIG. As good as However, the meniscus needs to exist in the installation region of the foreign material filling portion 3 during casting, and the meniscus fluctuates in the vertical direction during casting, so that the upper end portion of the foreign material filling portion 3 is always higher than the meniscus. It is preferable that the upper end portion of the different substance filling portion 3 is positioned about 10 mm above the meniscus so that the upper end portion is positioned above, and the upper end portion of the different substance filling portion 3 is positioned about 20 mm to 50 mm above the meniscus. Is more preferable.
この異種物質充填部３は、図２に示すように、鋳型長辺銅板１の内壁面側に加工された円形凹溝２の内部に、鋳型長辺銅板１を構成する銅合金の熱伝導率とは異なる熱伝導率の金属または非金属が充填されて形成されたものである。尚、この異種物質充填部は互いに独立するように凹溝を加工することがより好ましい。 As shown in FIG. 2, the dissimilar substance filling portion 3 has a thermal conductivity of the copper alloy constituting the long copper plate 1 in the circular groove 2 processed on the inner wall surface side of the long copper plate 1. It is formed by being filled with a metal or non-metal having a different thermal conductivity. In addition, it is more preferable to process the groove so that the different substance filling portions are independent of each other.
円形凹溝２の内部に充填される金属または非金属の熱伝導率は、一般的には、鋳型長辺銅板１を構成する銅合金の熱伝導率よりも低いが、例えば、鋳型長辺銅板１を構成する銅合金として熱伝導率の低い銅合金を使用した場合には、充填される金属または非金属の熱伝導率の方が高くなることもある。充填する物質が金属の場合には、鍍金処理または溶射処理によって充填し、充填する物質が非金属の場合には、円形凹溝２の形状に合わせて加工した非金属を円形凹溝２に嵌め込むなどして充填する。ここで、図２における符号４は、鋳型冷却水の流路を構成する、鋳型長辺銅板１の背面側に設置されたスリットであり、符号５は、鋳型長辺銅板１の背面と密着するバックプレートであり、スリット４を通る鋳型冷却水によって、鋳型長辺銅板１は冷却される。 The thermal conductivity of metal or nonmetal filled in the circular concave groove 2 is generally lower than the thermal conductivity of the copper alloy constituting the mold long-side copper plate 1, but for example, the mold long-side copper plate When a copper alloy having a low thermal conductivity is used as the copper alloy constituting 1, the thermal conductivity of the filled metal or nonmetal may be higher. When the material to be filled is metal, it is filled by plating or thermal spraying. When the material to be filled is non-metal, a non-metal processed according to the shape of the circular groove 2 is fitted into the circular groove 2. Fill and fill. Here, reference numeral 4 in FIG. 2 is a slit installed on the back side of the mold long-side copper plate 1 constituting the flow path of the mold cooling water, and reference numeral 5 is in close contact with the back surface of the mold long-side copper plate 1. The mold long-side copper plate 1 is cooled by mold cooling water which is a back plate and passes through the slit 4.
本実施形態に係る連続鋳造方法で使用する連続鋳造用鋳型において、鋳型銅板として使用する銅合金としては、一般的に連続鋳造用鋳型銅板として使用される、クロム（Ｃｒ）やジルコニウム（Ｚｒ）などを微量添加した銅合金を用いればよい。近年では、鋳型内の凝固の均一化または溶鋼中介在物の凝固シェルへの捕捉を防止するために、鋳型内の溶鋼を攪拌する電磁攪拌装置が設置されていることが一般的であり、電磁コイルから溶鋼への磁場強度の減衰を抑制するために、導電率を低減した銅合金が用いられている。この場合、導電率の低下に応じて熱伝導率も低減し、純銅（熱伝導率；３９８Ｗ／（ｍ×Ｋ））の１／２前後の熱伝導率の銅合金製鋳型銅板も使用されることがある。尚、鋳型銅板として使用される銅合金は、一般的に、純銅よりも熱伝導率が低い。 In the continuous casting mold used in the continuous casting method according to the present embodiment, as a copper alloy used as a casting copper plate, chromium (Cr), zirconium (Zr), etc. that are generally used as a casting copper plate for continuous casting A copper alloy with a small amount of added may be used. In recent years, an electromagnetic stirrer for stirring the molten steel in the mold is generally installed in order to make the solidification in the mold uniform or prevent the inclusions in the molten steel from being trapped in the solidified shell. In order to suppress the attenuation of the magnetic field strength from the coil to the molten steel, a copper alloy with reduced conductivity is used. In this case, the thermal conductivity is reduced as the conductivity decreases, and a copper alloy mold copper plate having a thermal conductivity of about 1/2 that of pure copper (thermal conductivity: 398 W / (mxK)) is also used. Sometimes. In addition, the copper alloy used as a mold copper plate generally has a lower thermal conductivity than pure copper.
本実施形態に係る連続鋳造方法で使用する連続鋳造用鋳型において、円形凹溝に充填する金属（以下、「充填金属」とも記載する）としては、銅合金よりも熱伝導率が低く、且つ、鍍金処理や溶射処理によって容易に充填することができるニッケル（Ｎｉ、熱伝導率；９０．５Ｗ／（ｍ×Ｋ））、ニッケル系合金、クロム（Ｃｒ、熱伝導率；６７Ｗ／（ｍ×Ｋ））、コバルト（Ｃｏ、熱伝導率；７０Ｗ／（ｍ×Ｋ））などが好適である。また、銅合金よりも熱伝導率が高い純銅を、円形凹溝に充填使用する金属として使用することもできる。純銅を充填した場合には、異種物質充填部３を設置した部位の方が鋳型銅板の部位よりも熱抵抗が小さくなる。 In the continuous casting mold used in the continuous casting method according to the present embodiment, the metal filling the circular groove (hereinafter also referred to as “filling metal”) has a lower thermal conductivity than the copper alloy, and Nickel (Ni, thermal conductivity: 90.5 W / (mxK)), nickel-based alloy, chromium (Cr, thermal conductivity: 67 W / (mxK) that can be easily filled by plating or thermal spraying )), Cobalt (Co, thermal conductivity; 70 W / (m × K)) and the like are suitable. Further, pure copper having a higher thermal conductivity than that of a copper alloy can be used as a metal used for filling circular concave grooves. When pure copper is filled, the thermal resistance of the part where the foreign substance filling part 3 is installed is smaller than the part of the mold copper plate.
また、円形凹溝に充填使用する非金属（以下、「充填非金属」とも記す）としては、ＢＮ、ＡｌＮ、ＺｒＯ２などの熱伝導率が小さいセラミックスが好適である。 Further, as the nonmetal used for filling the circular concave groove (hereinafter also referred to as “filling nonmetal”), ceramics having a low thermal conductivity such as BN, AlN, ZrO 2 and the like are suitable.
図３は、鋳型銅板よりも熱伝導率の低い物質が充填されて形成された異種物質充填部３を有する鋳型長辺銅板１の三箇所の位置における熱抵抗を、異種物質充填部３の位置に対応して概念的に示す図である。図３に示すように、異種物質充填部３の設置位置では熱抵抗が相対的に高くなる。 FIG. 3 shows the thermal resistance at three positions of the long copper plate 1 having the different material filling portion 3 formed by filling a material having a lower thermal conductivity than that of the mold copper plate, and the position of the different material filling portion 3. It is a figure shown notionally corresponding to. As shown in FIG. 3, the thermal resistance is relatively high at the installation position of the foreign substance filling unit 3.
複数の異種物質充填部３を、メニスカス位置を含んでメニスカス近傍の連続鋳造用鋳型の幅方向及び鋳造方向に設置することにより、図３に示すように、メニスカス近傍の鋳型幅方向及び鋳造方向における連続鋳造用鋳型の熱抵抗が周期的に増減する分布が形成される。これによって、メニスカス近傍、つまり、凝固初期での凝固シェルから連続鋳造用鋳型への熱流束が周期的に増減する分布が形成される。 As shown in FIG. 3, in the mold width direction and the casting direction in the vicinity of the meniscus, a plurality of different substance filling portions 3 are installed in the width direction and the casting direction of the continuous casting mold in the vicinity of the meniscus including the meniscus position. A distribution in which the thermal resistance of the continuous casting mold increases or decreases periodically is formed. This forms a distribution in which the heat flux from the solidified shell in the vicinity of the meniscus, that is, in the initial stage of solidification, to the continuous casting mold periodically increases and decreases.
尚、鋳型銅板よりも熱伝導率の高い物質を充填して異種物質充填部３を形成した場合には、図３とは異なり、異種物質充填部３の設置位置で熱抵抗が相対的に低くなるが、この場合も同様に、メニスカス近傍の鋳型幅方向及び鋳造方向における連続鋳造用鋳型の熱抵抗が周期的に増減する分布が形成される。 In addition, when the different material filling portion 3 is formed by filling a material having higher thermal conductivity than the mold copper plate, unlike FIG. 3, the thermal resistance is relatively low at the installation position of the different material filling portion 3. However, in this case as well, a distribution is formed in which the thermal resistance of the continuous casting mold in the mold width direction and the casting direction in the vicinity of the meniscus periodically increases and decreases.
この熱流束の周期的な増減により、δ鉄からγ鉄への変態（以下「δ／γ変態」と記す）によって発生する応力や熱応力が低減し、これらの応力によって生じる凝固シェルの変形が小さくなる。凝固シェルの変形が小さくなることで、凝固シェルの変形に起因する不均一な熱流束分布が均一化され、且つ、発生する応力が分散されて個々の歪量が小さくなる。その結果、凝固シェル表面における表面割れの発生が抑制される。 Due to the periodic increase and decrease of the heat flux, stress and thermal stress generated by transformation from δ iron to γ iron (hereinafter referred to as “δ / γ transformation”) are reduced, and deformation of the solidified shell caused by these stresses is reduced. Get smaller. By reducing the deformation of the solidified shell, the non-uniform heat flux distribution resulting from the deformation of the solidified shell is made uniform, and the generated stress is dispersed to reduce the amount of individual strain. As a result, the occurrence of surface cracks on the surface of the solidified shell is suppressed.
本実施形態においては、更に、凝固初期の抜熱量を適正化して凝固シェルに作用する応力の絶対値を制御するために、異種物質充填部３を配置した領域であって、メニスカスの下方５０ｍｍ位置における鋳型銅板と鋳型冷却水との間の熱流束の鋳型幅方向の平均値が、鋳片引き抜き速度に応じて定まる下記の（１）式を満足する範囲であり、且つ、メニスカスの下方５０ｍｍ位置における鋳型銅板と鋳型冷却水との間の熱流束の鋳型幅方向の標準偏差が、下記の（２）式を満足する範囲とする。 In the present embodiment, in addition, in order to optimize the amount of heat removal at the initial stage of solidification and to control the absolute value of the stress acting on the solidified shell, the dissimilar substance filling portion 3 is disposed at a position 50 mm below the meniscus. The average value of the heat flux between the mold copper plate and the mold cooling water in the mold width direction is within the range satisfying the following formula (1) determined according to the slab drawing speed, and the position 50 mm below the meniscus The standard deviation of the heat flux between the mold copper plate and the mold cooling water in the mold width direction is within a range satisfying the following expression (2).
０．５０×Ｖｃ＋０．５５≦Ｑ≦１．２０×Ｖｃ＋０．７５・・・（１）
σ≦０．２０・・・（２）
但し、（１）式において、Ｖｃは鋳片引き抜き速度（ｍ／ｍｉｎ）、Ｑは鋳型銅板と鋳型冷却水との間の熱流束の鋳型幅方向の平均値（ＭＷ／ｍ２）であり、また、（２）式において、σは鋳型銅板と鋳型冷却水との間の熱流束の鋳型幅方向の標準偏差（ＭＷ／ｍ２）である。
0.50 × Vc + 0.55 ≦ Q ≦ 1.20 × Vc + 0.75 (1)
σ ≦ 0.20 (2)
However, in the formula (1), Vc is the slab drawing speed (m / min), Q is the average value (MW / m 2 ) in the mold width direction of the heat flux between the mold copper plate and the mold cooling water, In the formula (2), σ is a standard deviation (MW / m 2 ) in the mold width direction of the heat flux between the mold copper plate and the mold cooling water.
本実施形態において、メニスカスの下方５０ｍｍ位置における鋳型銅板と鋳型冷却水との間の熱流束を対象とする理由は、連続鋳造用鋳型における熱流束はメニスカスの下方５０ｍｍ位置近傍で最大となり、凝固シェルに作用する応力は、この部位の熱流束の影響を受けることに基づく。 In the present embodiment, the reason for the heat flux between the mold copper plate and the mold cooling water at the position 50 mm below the meniscus is that the heat flux in the continuous casting mold is the maximum near the position 50 mm below the meniscus, and the solidified shell. The stress acting on is based on being affected by the heat flux at this site.
鋳型銅板と鋳型冷却水との間の熱流束を測定する方法として、鋳型銅板に熱電対を設置し、熱電対による鋳型銅板の温度測定値と鋳型冷却水の温度測定値との温度差から求める方法がある。但し、求められた熱流束は鋳型の幅方向位置で変化することが知られている。したがって、熱流束の鋳型幅方向の平均値Ｑを求めるためには、鋳型を鋳型幅方向で複数に分割し、分割したそれぞれの部位の鋳型銅板に熱電対を設置し、それぞれの熱電対による鋳型銅板温度の測定値に基づいて、分割したそれぞれの部位の熱流束を求める必要がある。得られた複数の熱流束データの平均値を採ることで、熱流束の鋳型幅方向の平均値Ｑが求められる。また、得られた複数の熱流束データから標準偏差σが求められる。 As a method of measuring the heat flux between the mold copper plate and the mold cooling water, a thermocouple is installed on the mold copper plate, and it is obtained from the temperature difference between the temperature measurement value of the mold copper plate and the mold cooling water measured by the thermocouple. There is a way. However, it is known that the obtained heat flux changes at the position in the width direction of the mold. Therefore, in order to obtain the average value Q of the heat flux in the mold width direction, the mold is divided into a plurality of molds in the mold width direction, and a thermocouple is installed on each of the divided mold copper plates. It is necessary to obtain the heat flux of each divided part based on the measured value of the copper plate temperature. The average value Q in the mold width direction of the heat flux is obtained by taking the average value of the obtained plurality of heat flux data. Further, the standard deviation σ is obtained from the obtained plurality of heat flux data.
この場合、鋳型幅方向の分割数が多いほど、熱流束の幅方向平均値Ｑの精度が高くなるので、本実施形態において、熱流束の鋳型幅方向の平均値Ｑを求めるにあたり、１００ｍｍ以下の間隔で鋳型を幅方向に分割することが好ましい。したがって、幅が２０００ｍｍ程度の鋳型長辺銅板では、鋳型幅方向で２０個以上に分割することが好ましい。尚、分割したそれぞれの部位における鋳型銅板と鋳型冷却水との間の熱流束は、「局所熱流束」とも呼ばれている。局所熱流束は、下記の（５）式によって求めることができる。 In this case, the greater the number of divisions in the mold width direction, the higher the accuracy of the average value Q of the heat flux in the width direction. Therefore, in this embodiment, the average value Q of the heat flux in the mold width direction is 100 mm or less. It is preferable to divide the mold in the width direction at intervals. Therefore, it is preferable to divide the long-side copper plate having a width of about 2000 mm into 20 pieces or more in the mold width direction. In addition, the heat flux between the mold copper plate and the mold cooling water in each divided part is also referred to as “local heat flux”. The local heat flux can be obtained by the following equation (5).
但し、（５）式において、ｑは局所熱流束（Ｗ／ｍ２）、ｈｗは鋳型銅板と鋳型冷却水と間の熱伝達係数（Ｗ／（ｍ２×Ｋ））、Ｚは熱電対先端とスリットとの間の距離（ｍ）、λｃは鋳型銅板の熱伝導率（Ｗ／（ｍ×Ｋ））、Ｔｃは鋳型銅板に埋め込んだ熱電対で測定した鋳型銅板温度（Ｋ）、Ｔｗは鋳型冷却水の温度（Ｋ）である。
Where q is the local heat flux (W / m 2 ), h w is the heat transfer coefficient (W / (m 2 × K)) between the mold copper plate and the mold cooling water, and Z is the thermocouple. The distance between the tip and the slit (m), λ c is the thermal conductivity (W / (m × K)) of the mold copper plate, and T c is the mold copper plate temperature (K) measured by a thermocouple embedded in the mold copper plate. , Tw is the temperature (K) of the mold cooling water.
ここで、（５）式の熱伝達係数ｈｗは、円管内の強制対流伝熱の場合には下記の（６）式で表される。 Here, (5) the heat transfer coefficient h w of expression, in the case of forced convection heat transfer of the circular tube is represented by the following formula (6).
ｈｗ＝０．０２３×（λｗ／ｄｗ）×（ρｗ×ｕｗ×ｄｗ／ηｗ）０．８×（ｃｗ×ηｗ／λｗ）０．３３・・・（６）
但し、（６）式において、λｗは鋳型冷却水の熱伝導率（Ｗ／（ｍ×Ｋ））、ｄｗはスリット断面積の相当直径（ｍ）、ρｗは鋳型冷却水の密度（ｋｇ／ｍ３）、ｕｗはスリットを通る鋳型冷却水の線流速（ｍ／ｓ）、ηｗは鋳型冷却水の粘度（Ｐａ・ｓ）、ｃｗは鋳型冷却水の比熱（Ｊ／（ｋｇ×Ｋ））である。
h w = 0.023 × (λ w / d w ) × (ρ w × u w × d w / η w ) 0.8 × (c w × η w / λ w ) 0.33 (6) )
In equation (6), λ w is the thermal conductivity (W / (m × K)) of the mold cooling water, d w is the equivalent diameter (m) of the slit cross-sectional area, and ρ w is the density of the mold cooling water ( kg / m 3 ), u w is the linear flow velocity (m / s) of the mold cooling water through the slit, η w is the viscosity (Pa · s) of the mold cooling water, and c w is the specific heat of the mold cooling water (J / ( kg × K)).
測定した局所熱流束ｑから熱流束の鋳型幅方向の平均値Ｑを求めるには、少なくとも、５秒間隔で６０セットの局所熱流束データを測定する必要がある。 In order to obtain the average value Q of the heat flux in the mold width direction from the measured local heat flux q, it is necessary to measure at least 60 sets of local heat flux data at intervals of 5 seconds.
本発明者らは、このようにして求められる平均値Ｑ及び標準偏差σの鋳片表面割れに及ぼす影響を調査した。具体的には、異種物質充填部３を形成する金属または非金属、及び、異種物質充填部３の直径ｄ、間隔Ｐまたは充填厚みＨを種々変更して、図１に示す連続鋳造用鋳型を製作し、この連続鋳造用鋳型を用いて中炭素鋼の連続鋳造を行い、鋳造後のスラブ鋳片の表面割れ発生状況を調査した。鋳片の表面割れの調査は、面積２１ｍ２以上の鋳片表面を染色浸透探傷検査によって検査し、検出された長さ１．０ｍｍ以上の縦割れの個数を測定し、この個数を鋳片の測定面積で除算したものを鋳片表面割れ個数密度と定義し、この鋳片表面割れ個数密度で評価した。 The present inventors investigated the influence of the average value Q and the standard deviation σ thus determined on the slab surface crack. Specifically, the continuous casting mold shown in FIG. 1 is obtained by variously changing the metal d or non-metal forming the foreign material filling portion 3 and the diameter d, interval P or filling thickness H of the foreign material filling portion 3. The medium carbon steel was continuously cast using this continuous casting mold, and the occurrence of surface cracks in the slab slab after the casting was investigated. The surface cracks of the slab are examined by inspecting the surface of a slab having an area of 21 m 2 or more by dye penetration inspection, measuring the number of detected vertical cracks having a length of 1.0 mm or more, and measuring this number of slabs. The product divided by the measurement area was defined as the slab surface crack number density, and this slab surface crack number density was evaluated.
図４は、鋳型銅板と鋳型冷却水との間の熱流束の鋳型幅方向の標準偏差σを０．２０以下とする条件で、鋳片引き抜き速度別に、メニスカスの下方５０ｍｍ位置における熱流束の鋳型幅方向の平均値Ｑの鋳片表面割れに及ぼす影響を調査した結果を示す図である。図４では、鋳片表面割れ個数密度が０．３個／ｍ２以下のデータと、０．３個／ｍ２超えのデータとを区別して表示している。尚、標準偏差σが０．２０以下のデータのみを選定した理由は、標準偏差σが０．２０を超えると、後述するように、鋳片表面割れ個数密度が０．３個／ｍ２よりも高くなり、鋳片の表面割れに及ぼす平均値Ｑの影響が不明確になることによる。 FIG. 4 shows a mold of heat flux at a position 50 mm below the meniscus for each slab drawing speed under the condition that the standard deviation σ in the mold width direction of the heat flux between the mold copper plate and the mold cooling water is 0.20 or less. It is a figure which shows the result of having investigated the influence which it has on the slab surface crack of the average value Q of the width direction. In FIG. 4, data having a slab surface crack number density of 0.3 pieces / m 2 or less and data exceeding 0.3 pieces / m 2 are displayed separately. The reason for selecting only data with a standard deviation σ of 0.20 or less is that when the standard deviation σ exceeds 0.20, the slab surface crack number density is 0.3 pieces / m 2 as will be described later. This is because the influence of the average value Q on the surface crack of the slab becomes unclear.
鋳片の表面割れ個数密度が０．３個／ｍ２以下のデータと０．３個／ｍ２超えのデータとの境界を回帰式によって求めると、図４に示すように、下限値として「Ｑ＝０．５０Ｖｃ＋０．５５」が求められ、一方、上限値として「Ｑ＝１．２０Ｖｃ＋０．７５」が求められた。即ち、メニスカスの下方５０ｍｍ位置における鋳型銅板と鋳型冷却水との間の熱流束の鋳型幅方向の平均値Ｑが、鋳片引き抜き速度に応じて定まる上記の（１）式を満足する範囲の場合に、鋳片の表面割れがより一層抑制されることが確認できた。 When the boundary between the data of the surface crack number density of the slab of 0.3 pieces / m 2 or less and the data of more than 0.3 pieces / m 2 is obtained by a regression equation, as shown in FIG. Q = 0.50V c +0.55 "is obtained, while the" Q = 1.20 V c +0.75 "was determined as the upper limit. That is, in the case where the average value Q in the mold width direction of the heat flux between the mold copper plate and the mold cooling water at the position 50 mm below the meniscus is in a range satisfying the above formula (1) determined according to the slab drawing speed. Further, it was confirmed that the surface crack of the slab was further suppressed.
これは、平均値Ｑが「０．５０Ｖｃ＋０．５５」未満の場合は、凝固シェルが薄すぎて、小さな応力でも割れが生成すると考えられる。一方、平均値Ｑが「１．２０Ｖｃ＋０．７５」を超える場合は、冷却速度が速すぎて、発生する応力が大きくなるためと考えられる。 This is considered that when the average value Q is less than “0.50 V c +0.55”, the solidified shell is too thin and cracks are generated even with a small stress. On the other hand, when the average value Q exceeds “1.20V c +0.75”, it is considered that the cooling rate is too high and the generated stress increases.
また、鋳片引き抜き速度と、メニスカスの下方５０ｍｍ位置における熱流束の鋳型幅方向の平均値Ｑとの関係が（１）式を満足する条件で、鋳型銅板と鋳型冷却水との間の熱流束の鋳型幅方向の標準偏差σの鋳片表面割れに及ぼす影響を調査した。調査結果を図５に示す。尚、鋳片引き抜き速度と平均値Ｑとの関係が（１）式を満足する条件のみを選定した理由は、前述したように、鋳片引き抜き速度と平均値Ｑとの関係が（１）式を満足しない場合は、鋳片表面割れ個数密度が０．３個／ｍ２よりも高くなり、鋳片の表面割れに及ぼす標準偏差σの影響が不明確になることによる。 Further, the heat flux between the mold copper plate and the mold cooling water under the condition that the relationship between the slab drawing speed and the average value Q in the mold width direction of the heat flux at the position 50 mm below the meniscus satisfies the formula (1). The effect of the standard deviation σ in the mold width direction on the slab surface crack was investigated. The survey results are shown in FIG. The reason why only the condition that the relationship between the slab drawing speed and the average value Q satisfies the equation (1) is selected is that, as described above, the relationship between the slab drawing speed and the average value Q is the equation (1). Is not satisfied, the slab surface crack number density is higher than 0.3 / m 2 , and the influence of the standard deviation σ on the slab surface crack becomes unclear.
図５に示すように、メニスカスの下方５０ｍｍ位置における熱流束の鋳型幅方向の標準偏差σが０．２０以下の場合に、鋳片の表面割れ個数密度が０．３個／ｍ２以下になることが確認できた。これは、標準偏差σが０．２０より大きい場合には、鋳型幅方向において局所熱流束ｑが大きくなる部位が発生し、その部位で鋳片に表面割れが発生すると考えられる。 As shown in FIG. 5, when the standard deviation σ in the mold width direction of the heat flux at a position 50 mm below the meniscus is 0.20 or less, the surface crack number density of the slab becomes 0.3 pieces / m 2 or less. I was able to confirm. When the standard deviation σ is larger than 0.20, it is considered that a part where the local heat flux q increases in the mold width direction and surface cracks occur in the slab at that part.
以上説明したように、本実施形態においては、メニスカスの下方５０ｍｍ位置における鋳型銅板と鋳型冷却水との間の熱流束の鋳型幅方向の平均値Ｑが、鋳片引き抜き速度Ｖｃに応じて定まる上記の（１）式を満足する範囲であり、且つ、メニスカスの下方５０ｍｍ位置における鋳型銅板と鋳型冷却水との間の熱流束の鋳型幅方向の標準偏差σが、上記の（２）式を満足する範囲であることが必要である。 As described above, in the present embodiment, the average value Q in the mold width direction of the heat flux between the mold copper plate and the mold cooling water at the position 50 mm below the meniscus is determined according to the slab drawing speed V c. The standard deviation σ in the mold width direction of the heat flux between the mold copper plate and the mold cooling water at the position 50 mm below the meniscus within the range satisfying the above expression (1) is the above expression (2). It is necessary to be in a satisfactory range.
図１及び図２では、異種物質充填部３の鋳型長辺銅板１の内壁面における形状が円形である例を示したが、当該形状は円形に限られない。例えば楕円形のような、所謂「角」を有していない円形に近い形状であれば、どのような形状であってもよい。以下、円形に近いものを「擬似円形」と称する。異種物質充填部３の形状が擬似円形の場合には、異種物質充填部３を形成させるための鋳型長辺銅板１の内壁面に加工される凹溝を「擬似円形凹溝」と称する。擬似円形とは、例えば楕円形や、角部を円や楕円とする長方形などの角部を有していない形状であり、更には、花びら模様のような形状であってもよい。擬似円形の大きさは、擬似円形の面積から求められる円相当径で評価する。この擬似円形の円相当径ｄは下記の（７）式で算出される。 1 and 2 show an example in which the shape of the inner wall surface of the long-side copper plate 1 of the mold of the foreign substance filling portion 3 is circular, but the shape is not limited to a circle. For example, any shape may be used as long as it is a shape close to a circle having no so-called “corner” such as an ellipse. Hereinafter, a shape close to a circle is referred to as a “pseudo circle”. In the case where the shape of the foreign material filling portion 3 is a pseudo circle, the groove processed on the inner wall surface of the long copper plate 1 for forming the foreign material filling portion 3 is referred to as a “pseudo circular groove”. The pseudo circle is, for example, an ellipse or a shape having no corners such as a rectangle whose corners are circles or ellipses, and may be a petal pattern. The size of the pseudo circle is evaluated by an equivalent circle diameter obtained from the area of the pseudo circle. The pseudo circular equivalent circle diameter d is calculated by the following equation (7).
円相当径ｄ＝（４×Ｓ／π）１／２・・・（７）
但し、（７）式において、Ｓは異種物質充填部３の面積（ｍｍ２）である。
Equivalent circle diameter d = (4 × S / π) 1/2 (7)
However, in the formula (7), S is the area (mm 2 ) of the foreign substance filling portion 3.
特許文献３及び特許文献４のように、縦溝或いは格子溝を施し、この溝に充填金属または充填非金属を配置した場合には、充填金属または充填非金属と鋳型銅板との境界面及び格子部の直交部において、充填金属または充填非金属と銅との熱歪差による応力が集中し、鋳型銅板表面に割れが発生するという問題が起こる。これに対して、本実施形態に係る連続鋳造用鋳型は、異種物質充填部３の形状を円形または擬似円形にしている。これにより、充填金属または充填非金属と銅との境界面は曲面状となるので、境界面で応力が集中しにくく、鋳型銅板表面に割れが発生しにくいという利点が発現する。尚、鋳型銅板の材質や鋳型銅板内部の水冷構造などにより、鋳型銅板表面の割れ発生を抑止可能な場合は、異種物質充填部の形状は円形または擬円形に限られることはない。 When a longitudinal groove or a lattice groove is provided as in Patent Document 3 and Patent Document 4 and a filling metal or a filling nonmetal is disposed in the groove, a boundary surface and a lattice between the filling metal or the filling nonmetal and the mold copper plate In the orthogonal part of the part, the stress due to the thermal strain difference between the filled metal or filled nonmetal and copper concentrates, causing a problem that cracks occur on the surface of the mold copper plate. On the other hand, in the continuous casting mold according to the present embodiment, the shape of the dissimilar substance filling portion 3 is circular or pseudo-circular. As a result, the boundary surface between the filled metal or filled nonmetal and copper has a curved surface, so that the stress is less likely to concentrate on the boundary surface and the advantage that cracks are less likely to occur on the surface of the mold copper plate. In addition, when the crack generation on the surface of the mold copper plate can be suppressed by the material of the mold copper plate or the water cooling structure inside the mold copper plate, the shape of the dissimilar substance filling portion is not limited to a circle or a pseudo circle.
異種物質充填部３の直径ｄ及び円相当径ｄは、２〜２０ｍｍであることが好ましい。異種物質充填部３の直径ｄ及び円相当径ｄを２ｍｍ以上とすることで、異種物質充填部３における熱流束の低下が十分となり、鋳片の表面割れ抑制効果を得ることができる。また、２ｍｍ以上とすることで、充填金属を鍍金処理や溶射処理によって円形凹溝２や擬似円形凹溝（図示せず）の内部に充填することが容易となる。一方、異種物質充填部３の直径及び円相当径を２０ｍｍ以下とすることで、異種物質充填部３における熱流束の低下が抑制され、つまり、異種物質充填部３での凝固遅れが抑制されて、その位置での凝固シェルへの応力集中が防止され、凝固シェルでの表面割れ発生を抑制できる。即ち、直径及び円相当径が２０ｍｍを超えると表面割れが増加する傾向があることから、異種物質充填部３の直径及び円相当径は２０ｍｍ以下にすることが好ましい。 It is preferable that the diameter d and the equivalent circle diameter d of the foreign substance filling portion 3 are 2 to 20 mm. By setting the diameter d and equivalent circle diameter d of the foreign material filling portion 3 to 2 mm or more, the heat flux in the foreign material filling portion 3 is sufficiently lowered, and the effect of suppressing the surface cracking of the slab can be obtained. Moreover, by setting it as 2 mm or more, it becomes easy to fill a filling metal into the inside of the circular ditch | groove 2 or a pseudo-circular ditch | groove (not shown) by a plating process or a thermal spraying process. On the other hand, by setting the diameter and equivalent circle diameter of the foreign material filling portion 3 to 20 mm or less, a decrease in heat flux in the foreign material filling portion 3 is suppressed, that is, a solidification delay in the foreign material filling portion 3 is suppressed. The concentration of stress on the solidified shell at that position is prevented, and the occurrence of surface cracks in the solidified shell can be suppressed. That is, when the diameter and the equivalent circle diameter exceed 20 mm, surface cracks tend to increase. Therefore, the diameter and equivalent circle diameter of the dissimilar substance filling portion 3 are preferably 20 mm or less.
異種物質充填部３の充填厚みＨは０．５ｍｍ以上とすることが好ましい。充填厚みＨを０．５ｍｍ以上とすることで、異種物質充填部３における熱流束の低下が十分となり、鋳片の表面割れ抑制効果を得ることができる。 The filling thickness H of the foreign substance filling portion 3 is preferably 0.5 mm or more. By setting the filling thickness H to 0.5 mm or more, the heat flux in the foreign substance filling portion 3 is sufficiently lowered, and the effect of suppressing the surface cracking of the slab can be obtained.
また、異種物質充填部３の充填厚みＨは、異種物質充填部３の直径ｄ以下及び円相当径ｄ以下にすることが好ましい。充填厚みＨを異種物質充填部３の直径ｄ及び円相当径ｄと同等、またはそれらよりも小さくするので、鍍金処理や溶射処理による円形凹溝及び擬似円形凹溝への充填金属の充填が容易となり、且つ、充填金属と鋳型銅板との間に隙間や割れが生じることもない。充填金属と鋳型銅板との間に隙間や割れが生じた場合には、充填金属の亀裂や剥離が生じ、鋳型寿命の低下、鋳片の割れ、更には拘束性ブレークアウトの原因となる。 Moreover, it is preferable that the filling thickness H of the foreign substance filling portion 3 is not more than the diameter d of the foreign substance filling portion 3 and the equivalent circle diameter d or less. Since the filling thickness H is equal to or smaller than the diameter d and equivalent circle diameter d of the different substance filling portion 3, filling of the filling metal into the circular concave groove and the pseudo circular concave groove by plating or spraying is easy. In addition, there are no gaps or cracks between the filling metal and the mold copper plate. When a gap or crack occurs between the filling metal and the mold copper plate, the filling metal cracks or peels off, causing a reduction in mold life, cracking of the cast piece, and further a restrictive breakout.
異種物質充填部同士の間隔Ｐは、異種物質充填部３の直径ｄ及び円相当径ｄの０．２５倍以上であることが好ましい。ここで、異種物質充填部同士の間隔Ｐとは、図１に示すように、隣り合う異種物質充填部３の端部間の最短距離である。異種物質充填部同士の間隔Ｐを「０．２５×ｄ」以上とすることで、間隔が十分に大きく、異種物質充填部３における熱流束と銅合金部（異種物質充填部３が形成されていない部位）の熱流束との差が大きくなり、鋳片の表面割れ抑制効果を得ることができる。異種物質充填部同士の間隔Ｐの上限値は特に定めなくてよいが、間隔Ｐが大きくなると、異種物質充填部３の面積率が低下するので「２．０×ｄ」以下にすることが好ましい。 The distance P between the different substance filling portions is preferably 0.25 times or more the diameter d and equivalent circle diameter d of the different substance filling portion 3. Here, the interval P between the different substance filling parts is the shortest distance between the end parts of the adjacent different substance filling parts 3 as shown in FIG. By setting the interval P between the different substance filling portions to be “0.25 × d” or more, the interval is sufficiently large, and the heat flux and the copper alloy portion (the different substance filling portion 3 is formed in the different substance filling portion 3). The difference from the heat flux of the non-part) becomes large, and the effect of suppressing the surface cracking of the slab can be obtained. The upper limit value of the interval P between the different substance filling portions may not be determined. However, since the area ratio of the different substance filling portion 3 is reduced when the interval P is increased, it is preferably set to “2.0 × d” or less. .
異種物質充填部３の配列は、図１に示すような千鳥配列が好ましいが、千鳥配列に限らず、異種物質充填部同士の上記間隔Ｐを満たす配列であれば、どのような配列でもよい。 The arrangement of the different substance filling portions 3 is preferably a zigzag arrangement as shown in FIG. 1, but is not limited to the zigzag arrangement and may be any arrangement as long as the arrangement satisfies the interval P between the different substance filling portions.
異種物質充填部３が配置された領域内の鋳型銅板内壁面の面積Ａ（ｍｍ２）に対する、全ての異種物質充填部３の面積の総和Ｂ（ｍｍ２）の比である面積率Ｓ（Ｓ＝（Ｂ／Ａ）×１００）は、１０％以上であることが好ましい。面積率Ｓを１０％以上確保することで、熱流束の小さい異種物質充填部３の占める面積が確保され、異種物質充填部３と銅合金部とで熱流束差が得られ、鋳片の表面割れ抑制効果を安定して得ることができる。ところで、鋼の連続鋳造における凝固シェルの凝固厚みは、下記の（８）式によって算出される。 Area ratio S (S) which is the ratio of the total area B (mm 2 ) of the areas of all the different material filling portions 3 to the area A (mm 2 ) of the inner wall surface of the mold copper plate in the region where the different material filling portions 3 are arranged. = (B / A) × 100) is preferably 10% or more. By securing an area ratio S of 10% or more, the area occupied by the dissimilar substance filling part 3 having a small heat flux is ensured, and a heat flux difference is obtained between the dissimilar substance filling part 3 and the copper alloy part. A crack suppressing effect can be obtained stably. By the way, the solidification thickness of the solidified shell in continuous casting of steel is calculated by the following equation (8).
Ｄｓ＝Ｋ×ｔ０．５・・・（８）
但し、（８）式において、Ｄｓは凝固シェルの凝固厚み（ｍｍ）、Ｋは凝固定数（ｍｍ／ｍｉｎ０．５）、ｔは凝固時間（ｍｉｎ）である。
D s = K × t 0.5 (8)
In equation (8), D s is the solidification thickness (mm) of the solidified shell, K is the solidification constant (mm / min 0.5 ), and t is the solidification time (min).
通常、凝固係数Ｋは、鋳型内と二次冷却帯とで異なり、鋳型内では鋳型条件に応じて２０〜２５ｍｍ／ｍｉｎ０．５程度の或る一定値、二次冷却帯では冷却水量に応じて２５〜３０ｍｍ／ｍｉｎ０．５程度の或る一定値である。 Usually, the solidification coefficient K differs between the mold and the secondary cooling zone, and within the mold, a certain constant value of about 20 to 25 mm / min 0.5 depending on the mold conditions, and depending on the amount of cooling water in the secondary cooling zone. And a certain constant value of about 0.5 to 30 mm / min 0.5 .
しかしながら、本実施形態では、鋳型銅板内壁面に異種物質充填部３を配置しており、異種物質充填部３が配置された領域と、異種物質充填部３が配置されていない領域とで、それぞれの熱流速が異なるので、両者における凝固シェルの抜熱量が異なる。このため、異種物質充填部３が配置された領域を通過するときの凝固シェルの凝固係数Ｋと、異種物質充填部が配置されていない領域を通過するときの凝固シェルの凝固係数Ｋとは自ずと異なる。 However, in this embodiment, the dissimilar substance filling part 3 is arranged on the inner wall surface of the mold copper plate, and the region where the dissimilar substance filling part 3 is arranged and the region where the dissimilar substance filling part 3 is not arranged respectively. Since the heat flow rates of the solidified shells are different, the amount of heat removed from the solidified shell is different. For this reason, the solidification coefficient K of the solidified shell when passing through the region where the foreign substance filling part 3 is disposed and the solidification coefficient K of the solidified shell when passing through the region where the foreign substance filling part is not disposed are naturally. Different.
本発明者らは、異種物質充填部３が配置された領域を通過するときの凝固シェルの凝固係数をＫ（Ｃ）とし、異種物質充填部３が配置されていない領域を通過するときの凝固シェルの凝固係数をＫ（Ｏ）とし、２つの領域における凝固係数Ｋの違いが、鋳片表面割れに及ぼす影響を調査した。この場合、異種物質充填部３の充填金属または充填非金属の熱伝導率を鋳型銅板の熱伝導率よりも小さくすると、凝固係数Ｋ（Ｃ）は凝固係数Ｋ（Ｏ）よりも小さくなり、異種物質充填部３の充填金属または充填非金属の熱伝導率を鋳型銅板の熱伝導率よりも大きくすると、凝固係数Ｋ（Ｃ）は凝固係数Ｋ（Ｏ）よりも大きくなる。 The inventors set the solidification coefficient of the solidified shell when passing through the region where the different substance filling portion 3 is disposed as K (C), and solidify when passing through the region where the different substance filling portion 3 is not arranged. The effect of the difference in the solidification coefficient K in the two regions on the slab surface crack was investigated with the solidification coefficient of the shell being K (O). In this case, if the thermal conductivity of the filled metal or filled nonmetal in the different substance filling portion 3 is made smaller than the thermal conductivity of the mold copper plate, the solidification coefficient K (C) becomes smaller than the solidification coefficient K (O). When the thermal conductivity of the filled metal or filled nonmetal in the material filling portion 3 is made larger than the thermal conductivity of the mold copper plate, the solidification coefficient K (C) becomes larger than the solidification coefficient K (O).
ここで、凝固係数Ｋ（Ｃ）及び凝固係数Ｋ（Ｏ）は、連続鋳造時に鋳型内に鉄−硫黄合金を添加し、鋳造後の鋳片内の硫黄濃度分布に基づいて、異種物質充填部３が配置された領域での凝固シェル厚みＤｓ、及び、異種物質充填部３が配置されていない領域での凝固シェル厚みＤｓを求め、求めた凝固シェル厚みＤｓから下記の（９）式を用いて算出した。 Here, the solidification coefficient K (C) and the solidification coefficient K (O) are obtained by adding an iron-sulfur alloy into the mold during continuous casting, and based on the sulfur concentration distribution in the cast slab after casting. solidified shell thickness D s at 3 is arranged regions, and obtains the solidified shell thickness D s in a region where different materials filling unit 3 is not arranged, the solidified shell thickness D s obtained the following (9) Calculated using the formula.
Ｙ＝Ｖｃ×（Ｄｓ／Ｋ）２・・・（９）
但し、（９）式において、Ｙは凝固シェル厚みを測定した位置のメニスカスからの距離（ｍ）、Ｖｃは鋳片引き抜き速度（ｍ／ｍｉｎ）、Ｄｓは凝固シェル厚み（ｍｍ）、Ｋは凝固係数（ｍｍ／ｍｉｎ０．５）である。
Y = V c × (D s / K) 2 (9)
However, in (9), Y is the distance from the meniscus position of the measurement of the solidified shell thickness (m), V c is the slab drawing speed (m / min), D s is solidified shell thickness (mm), K Is a solidification coefficient (mm / min 0.5 ).
調査結果を図６及び図７に示す。図６は、凝固係数Ｋ（Ｃ）が凝固係数Ｋ（Ｏ）よりも小さい場合であり、図７は、凝固係数Ｋ（Ｃ）が凝固係数Ｋ（Ｏ）よりも大きい場合である。図６及び図７に示すように、凝固係数Ｋ（Ｃ）と凝固係数Ｋ（Ｏ）とが、下記の（３）式または（４）式を満足するときに、鋳片の表面割れが抑制されることがわかった。 The investigation results are shown in FIGS. FIG. 6 shows a case where the solidification coefficient K (C) is smaller than the solidification coefficient K (O), and FIG. 7 shows a case where the solidification coefficient K (C) is larger than the solidification coefficient K (O). As shown in FIGS. 6 and 7, when the solidification coefficient K (C) and the solidification coefficient K (O) satisfy the following formula (3) or (4), the surface cracking of the slab is suppressed. I found out that
０．６≦Ｋ（Ｃ）／Ｋ（Ｏ）≦０．９５（但し、Ｋ（Ｃ）＜Ｋ（Ｏ）の場合）・・・（３）
０．６≦Ｋ（Ｏ）／Ｋ（Ｃ）≦０．９５（但し、Ｋ（Ｃ）＞Ｋ（Ｏ）の場合）・・・（４）
0.6 ≦ K (C) / K (O) ≦ 0.95 (provided that K (C) <K (O)) (3)
0.6 ≦ K (O) / K (C) ≦ 0.95 (provided that K (C)> K (O)) (4)
両者の比が０．６未満になる場合は、極端に緩冷却または極端に強冷却になる領域が発生し、極端な緩冷却が生ずる部位では、凝固シェル厚みが薄いことに起因するブレークアウトの懸念があり、極端な強冷却が生じる部位では、発生する応力が大きく、鋳片に表面割れが発生する懸念がある。一方、両者の比が０．９５よりも大きい場合は、異種物質充填部３を配置した効果が十分に得られず、鋳片の表面割れを抑制できない。 When the ratio between the two is less than 0.6, an extremely slow cooling or extremely strong cooling region is generated, and a breakout due to a thin solidified shell thickness occurs at a site where extreme slow cooling occurs. There is a concern, and in a portion where extreme strong cooling occurs, the generated stress is large, and there is a concern that surface cracks occur in the slab. On the other hand, when the ratio of both is larger than 0.95, the effect of disposing the different substance filling portion 3 cannot be sufficiently obtained, and the surface crack of the slab cannot be suppressed.
凝固係数Ｋ（Ｃ）と凝固係数Ｋ（Ｏ）との比の調整は、異種物質充填部３に充填する金属または非金属の種類、異種物質充填部３の直径ｄ、間隔Ｐ、充填厚みＨなどを適宜選定し、異種物質充填部３が配置された領域の熱流束と、異種物質充填部３が配置されていない領域の熱流束とを調整することによって、行うことができる。 Adjustment of the ratio between the solidification coefficient K (C) and the solidification coefficient K (O) is performed by adjusting the type of metal or non-metal filled in the foreign material filling portion 3, the diameter d, the spacing P, the filling thickness H of the foreign material filling portion 3. And the like, and the heat flux in the region where the different substance filling portion 3 is arranged and the heat flux in the region where the different substance filling portion 3 is not arranged can be adjusted.
また、図８に示すように、異種物質充填部３を形成させた鋳型銅板の内壁面に、凝固シェルによる磨耗や熱履歴による鋳型表面の割れを抑制することを目的として、鍍金層６を設けることが好ましい。この鍍金層６は、一般的に用いられるニッケルまたはニッケルを含有する合金、例えば、ニッケル−コバルト合金（Ｎｉ−Ｃｏ合金）やニッケル−クロム合金（Ｎｉ−Ｃｒ合金）などを鍍金処理することで得られる。 Further, as shown in FIG. 8, a plating layer 6 is provided on the inner wall surface of the mold copper plate on which the foreign substance filling portion 3 is formed for the purpose of suppressing wear by the solidified shell and cracking of the mold surface due to thermal history. It is preferable. The plating layer 6 is obtained by plating a commonly used nickel or nickel-containing alloy such as a nickel-cobalt alloy (Ni-Co alloy) or a nickel-chromium alloy (Ni-Cr alloy). It is done.
図９に、鋳型銅板内壁面の全面にニッケルを含有する合金の鍍金層６を形成する際に、鍍金層６の厚みｈを変更し、鋳型銅板表面に発生する亀裂の深さを調査した結果を示す。図９に示すように、鍍金層６の厚みｈが０．１ｍｍ以上３．０ｍｍ以下の場合に、亀裂の平均深さが小さくなることがわかった。 FIG. 9 shows the result of investigating the depth of cracks generated on the surface of the mold copper plate by changing the thickness h of the plating layer 6 when forming the plating layer 6 of the alloy containing nickel on the entire inner wall surface of the mold copper plate. Indicates. As shown in FIG. 9, when the thickness h of the plating layer 6 was 0.1 mm or more and 3.0 mm or less, it turned out that the average depth of a crack becomes small.
鍍金層６の厚みｈが０．１ｍｍ未満の場合は、厚みｈが小さすぎるために、鍍金層６が磨耗し、これにより鋳型銅板に亀裂が発生しやすくなると考えられる。一方、鍍金層６の厚みｈが３．０ｍｍより大きい場合は、鋳造中に鍍金層６の表面温度が高くなり、これにより鋳型銅板に亀裂が発生しやすくなると考えられる。鍍金層６の厚みｈが０．１ｍｍ以上３．０ｍｍ以下である限り、鍍金層６は鋳型上端から下端まで同一の厚みであっても、上端から下端にかけて厚みが異なっていてもよい。 When the thickness h of the plating layer 6 is less than 0.1 mm, it is considered that the plating layer 6 is worn out because the thickness h is too small, and cracks are likely to occur in the mold copper plate. On the other hand, when the thickness h of the plating layer 6 is larger than 3.0 mm, it is considered that the surface temperature of the plating layer 6 becomes high during casting, and cracks are likely to occur in the mold copper plate. As long as the thickness h of the plating layer 6 is 0.1 mm or more and 3.0 mm or less, the plating layer 6 may have the same thickness from the upper end to the lower end of the mold or may have a different thickness from the upper end to the lower end.
本実施形態に係る連続鋳造方法は、特に、表面割れ感受性が高い、炭素含有量が０．０８〜０．１７質量％の中炭素鋼のスラブ鋳片（厚み；２００ｍｍ以上）を連続鋳造する際に適用することが好ましい。従来、中炭素鋼のスラブ鋳片を連続鋳造する場合は、鋳片の表面割れを防止するために、鋳片引き抜き速度を低速化することが一般的であるが、本発明を適用することで鋳片表面割れが防止できるので、１．５ｍ／ｍｉｎ以上の鋳片引き抜き速度であっても、表面割れのない、または表面割れの著しく少ない鋳片を連続鋳造することが実現される。 The continuous casting method according to the present embodiment is particularly suitable for continuous casting of slab slabs (thickness: 200 mm or more) of medium carbon steel having a high surface cracking sensitivity and a carbon content of 0.08 to 0.17% by mass. It is preferable to apply to. Conventionally, when continuously casting slab slabs of medium carbon steel, it is common to reduce the slab drawing speed in order to prevent surface cracking of the slab, but by applying the present invention, Since slab surface cracks can be prevented, continuous casting of slabs with no surface cracks or significantly less surface cracks can be realized even at a slab drawing speed of 1.5 m / min or more.
以上説明したように、本実施形態に係る連続鋳造方法は、複数個の異種物質充填部３を、少なくともメニスカスからメニスカスの下方３００ｍｍの位置までの範囲に有する連続鋳造用鋳型を用い、メニスカスの下方５０ｍｍ位置における鋳型銅板と鋳型冷却水との間の熱流束の鋳型幅方向の平均値、及び、メニスカスの下方５０ｍｍ位置における鋳型銅板と鋳型冷却水との間の熱流束の鋳型幅方向の標準偏差を所定の値に制御するので、メニスカス近傍の鋳型幅方向及び鋳造方向における連続鋳造用鋳型の熱抵抗が、その値を所定の範囲内として周期的に増減し、これによって、メニスカス近傍、つまり、凝固初期での凝固シェルから連続鋳造用鋳型への熱流束が周期的に増減する。この熱流束の周期的な増減により、δ／γ変態による応力や熱応力が低減し、これらの応力によって生じる凝固シェルの変形が小さくなり、凝固シェルの変形が小さくなることで、凝固シェルの変形に起因する不均一な熱流束分布が均一化され、且つ、発生する応力が分散されて個々の歪量が小さくなる。その結果、凝固シェル表面における割れの発生が抑制される。 As described above, the continuous casting method according to the present embodiment uses a continuous casting mold having a plurality of different material filling portions 3 at least in a range from the meniscus to a position 300 mm below the meniscus, and below the meniscus. The average value in the mold width direction of the heat flux between the mold copper plate and the mold cooling water at the 50 mm position, and the standard deviation in the mold width direction of the heat flux between the mold copper plate and the mold cooling water at the 50 mm position below the meniscus. Is controlled to a predetermined value, so that the thermal resistance of the continuous casting mold in the mold width direction and the casting direction in the vicinity of the meniscus periodically increases and decreases within the predetermined range, thereby the vicinity of the meniscus, that is, The heat flux from the solidified shell to the continuous casting mold in the initial stage of solidification increases and decreases periodically. Due to the periodic increase / decrease of the heat flux, the stress and thermal stress due to the δ / γ transformation are reduced, the deformation of the solidified shell caused by these stresses is reduced, and the deformation of the solidified shell is reduced. The non-uniform heat flux distribution resulting from this is made uniform, and the generated stress is dispersed to reduce the amount of individual strain. As a result, the occurrence of cracks on the surface of the solidified shell is suppressed.
尚、図１では、同一形状の異種物質充填部３を鋳造方向または鋳型幅方向に設置した例を示したが、異種物質充填部３の形状は、同一でなくてもよい。但し、いずれの異種物質充填部３の直径ｄまたは円相当径ｄは２〜２０ｍｍであることが好ましい。また、異種物質充填部３の充填厚みＨも鋳造方向または鋳型幅方向に同一としなくてよく、個々の異種物質充填部３で充填厚みＨが異なっていてもよい。但し、いずれの異種物質充填部３の充填厚みＨも０．５ｍｍ以上であることが好ましい。また更に、図１では、鋳造方向または鋳型幅方向に同一間隔で異種物質充填部３を設置した例を示したが、同一間隔で異種物質充填部３を設置しなくてもよい。但し、この場合も、異種物質充填部同士の間隔Ｐは異種物質充填部３の直径ｄ及び円相当径ｄの０．２５倍以上であることが好ましい。 Although FIG. 1 shows an example in which the same shape of the different material filling portion 3 is installed in the casting direction or the mold width direction, the shape of the different material filling portion 3 may not be the same. However, it is preferable that the diameter d or the equivalent circle diameter d of any of the different substance filling portions 3 is 2 to 20 mm. Further, the filling thickness H of the different material filling portion 3 may not be the same in the casting direction or the mold width direction, and the filling thickness H may be different in each different material filling portion 3. However, the filling thickness H of any dissimilar substance filling portion 3 is also preferably 0.5 mm or more. Furthermore, although FIG. 1 shows an example in which the different substance filling portions 3 are installed at the same interval in the casting direction or the mold width direction, the different substance filling portions 3 may not be installed at the same interval. However, also in this case, it is preferable that the distance P between the different material filling portions is 0.25 times or more the diameter d of the different material filling portion 3 and the equivalent circle diameter d.
また、上記説明はスラブ鋳片の連続鋳造に関して行ったが、本実施形態に係る連続鋳造方法はスラブ鋳片の連続鋳造に限定されるものではなく、ブルーム鋳片やビレット鋳片の連続鋳造においても上記に沿って適用することができる。 Moreover, although the said description was performed regarding the continuous casting of a slab slab, the continuous casting method which concerns on this embodiment is not limited to the continuous casting of a slab slab, In continuous casting of a bloom slab or a billet slab Can also be applied in line with the above.
中炭素鋼（化学成分、Ｃ：０．０８〜０．１７質量％、Ｓｉ：０．１０〜０．３０質量％、Ｍｎ：０．５０〜１．２０質量％、Ｐ：０．０１０〜０．０３０質量％、Ｓ：０．００５〜０．０１５質量％、Ａｌ：０．０２０〜０．０４０質量％）を、内壁面に種々の条件で異種物質充填部が設置された水冷式銅合金製鋳型を用いて連続鋳造し、鋳造後のスラブ鋳片の表面割れを調査する試験を行った。用いた水冷式銅合金製鋳型は、長辺長さが１．８ｍ、短辺長さが０．２２ｍの内面空間サイズを有する鋳型である。 Medium carbon steel (Chemical component, C: 0.08 to 0.17 mass%, Si: 0.10 to 0.30 mass%, Mn: 0.50 to 1.20 mass%, P: 0.010 to 0 0.030% by mass, S: 0.005 to 0.015% by mass, Al: 0.020 to 0.040% by mass), and a water-cooled copper alloy in which different-material-filled portions are installed on the inner wall surface under various conditions A test was conducted to investigate the surface cracking of the slab slab after casting using a casting mold. The water-cooled copper alloy mold used is a mold having an inner space size with a long side length of 1.8 m and a short side length of 0.22 m.
使用した水冷式銅合金製鋳型の上端から下端までの長さは９５０ｍｍであり、定常鋳造時のメニスカス（鋳型内溶鋼湯面）の位置を、鋳型上端から１００ｍｍ下方位置に設定した。鋳型銅板としては、熱伝導率が２９８．５Ｗ／（ｍ×Ｋ）である銅合金を用い、鋳型上端から６０ｍｍ下方の位置から、鋳型上端から５００ｍｍ下方の位置までの領域に異種物質充填部を配置した。異種物質充填部の充填金属として、純ニッケル（熱伝導率；９０．５Ｗ／（ｍ×Ｋ））及び純銅（熱伝導率；３９８Ｗ／（ｍ×Ｋ））を使用した。異種物質充填部の設置後、鋳型銅板内壁面の全面にＮｉ−Ｃｏ合金を鍍金し、鍍金層を施工した。 The length from the upper end to the lower end of the water-cooled copper alloy mold used was 950 mm, and the position of the meniscus (molten steel surface in the mold) during steady casting was set at a position 100 mm below the upper end of the mold. As the mold copper plate, a copper alloy having a thermal conductivity of 298.5 W / (m × K) is used, and a foreign substance filling portion is provided in a region from a position 60 mm below the mold upper end to a position 500 mm below the mold upper end. Arranged. Pure nickel (thermal conductivity: 90.5 W / (m × K)) and pure copper (thermal conductivity: 398 W / (m × K)) were used as the filler metal in the different-material filling part. After the dissimilar substance filling portion was installed, a Ni—Co alloy was plated on the entire inner wall surface of the mold copper plate, and a plating layer was applied.
連続鋳造終了後、鋳片表面の２１ｍ２以上の面積を染色浸透探傷検査によって検査し、１．０ｍｍ以上の長さの表面割れの個数を測定し、その総和を鋳片測定面積で除算して得られる鋳片表面割れ個数密度を用いて表面割れの発生状況を評価した。 After completion of continuous casting, the surface area of 21 m 2 or more on the surface of the slab is inspected by dye penetration inspection, the number of surface cracks with a length of 1.0 mm or more is measured, and the sum is divided by the slab measurement area. Using the resulting slab surface crack number density, the occurrence of surface cracks was evaluated.
表１に、本発明例１〜７、比較例１〜８及び従来例における、鋳片引き抜き速度、及び、メニスカスの下方５０ｍｍ位置での鋳型銅板と鋳型冷却水との間の熱流束の鋳型幅方向の平均値Ｑの実測値、熱流束の鋳型幅方向の標準偏差σの実測値、鍍金層の厚み、凝固係数Ｋ（Ｃ）、凝固係数Ｋ（Ｏ）などの鋳型冷却条件を示す。尚、比較例は、異種物質充填部を有する水冷式銅合金製鋳型を使用するものの本発明の範囲を満足しない鋳型冷却条件で鋳造した試験、従来例は、異種物質充填部を有していない水冷式銅合金製鋳型を使用した試験である。 Table 1 shows the casting width of the slab and the mold width of the heat flux between the mold copper plate and the mold cooling water at a position 50 mm below the meniscus in Examples 1 to 7 of the present invention, Comparative Examples 1 to 8 and the conventional example. The mold cooling conditions such as the measured value of the average value Q in the direction, the measured value of the standard deviation σ in the mold width direction of the heat flux, the thickness of the plating layer, the solidification coefficient K (C), and the solidification coefficient K (O) are shown. The comparative example uses a water-cooled copper alloy mold having a foreign material filling portion, but the test is performed under a mold cooling condition that does not satisfy the scope of the present invention, and the conventional example does not have a foreign material filling portion. This is a test using a water-cooled copper alloy mold.
図１０に、本発明例１〜７、比較例１〜８及び従来例におけるスラブ鋳片の鋳片表面割れ個数密度を比較して示す。図１０からも明らかなように、本発明例１〜７では、鋳片表面割れ個数密度はいずれも０．３個／ｍ２以下であり、鋳片の表面割れが抑制されることが確認できた。これに対して、比較例１〜８は、従来例に比べると鋳片の表面割れは減少したが、本発明例１〜７に比較すると鋳片表面割れが多発した。 In FIG. 10, the slab surface crack number density of the slab slab in this invention example 1-7, comparative examples 1-8, and a prior art example is compared and shown. As is clear from FIG. 10, in Examples 1 to 7 of the present invention, the number density of slab surface cracks is 0.3 pieces / m 2 or less, and it can be confirmed that surface cracks of the slab are suppressed. It was. On the other hand, in Comparative Examples 1 to 8, the surface cracks of the slab were reduced as compared with the conventional examples, but the slab surface cracks were frequently generated as compared with Examples 1 to 7 of the present invention.
１ 鋳型長辺銅板
２ 円形凹溝
３ 異種物質充填部
４ スリット
５ バックプレート
６ 鍍金層
DESCRIPTION OF SYMBOLS 1 Mold long side copper plate 2 Circular groove 3 Dissimilar substance filling part 4 Slit 5 Back plate 6 Sheet metal layer
Claims (6)
前記異種物質充填部を配置した領域であって、前記メニスカスの下方５０ｍｍ位置における鋳型銅板と鋳型冷却水との間の熱流束の鋳型幅方向の平均値が、鋳片引き抜き速度に応じて定まる下記の（１）式を満足する範囲であり、且つ、前記メニスカスの下方５０ｍｍ位置における鋳型銅板と鋳型冷却水との間の熱流束の鋳型幅方向の標準偏差が、下記の（２）式を満足する範囲であることを特徴とする、鋼の連続鋳造方法。
０．５０×Ｖｃ＋０．５５≦Ｑ≦１．２０×Ｖｃ＋０．７５・・・（１）
σ≦０．２０・・・（２）
但し、（１）式において、Ｖｃは鋳片引き抜き速度（ｍ／ｍｉｎ）、Ｑは鋳型銅板と鋳型冷却水との間の熱流束の鋳型幅方向の平均値（ＭＷ／ｍ２）であり、また、（２）式において、σは鋳型銅板と鋳型冷却水との間の熱流束の鋳型幅方向の標準偏差（ＭＷ／ｍ２）である。 A plurality of different types in which the entire inner wall surface of the copper alloy mold copper plate in the region from at least the meniscus to a position 300 mm below the meniscus is filled with a metal or nonmetal having a thermal conductivity different from the thermal conductivity of the mold copper plate. Using a water-cooled copper alloy mold having a material filling portion, a continuous casting method of steel in which molten steel in a tundish is poured into the mold and continuously cast,
The region where the different substance filling portion is arranged, and the average value in the mold width direction of the heat flux between the mold copper plate and the mold cooling water at the position 50 mm below the meniscus is determined according to the slab drawing speed The standard deviation in the mold width direction of the heat flux between the mold copper plate and the mold cooling water at the position 50 mm below the meniscus satisfies the following expression (2). A continuous casting method of steel, characterized in that the range is to be performed.
0.50 × Vc + 0.55 ≦ Q ≦ 1.20 × Vc + 0.75 (1)
σ ≦ 0.20 (2)
However, in the formula (1), Vc is the slab drawing speed (m / min), Q is the average value (MW / m 2 ) in the mold width direction of the heat flux between the mold copper plate and the mold cooling water, In the formula (2), σ is a standard deviation (MW / m 2 ) in the mold width direction of the heat flux between the mold copper plate and the mold cooling water.
０．６≦Ｋ（Ｃ）／Ｋ（Ｏ）≦０．９５（但し、Ｋ（Ｃ）＜Ｋ（Ｏ）の場合）・・・（３）
０．６≦Ｋ（Ｏ）／Ｋ（Ｃ）≦０．９５（但し、Ｋ（Ｃ）＞Ｋ（Ｏ）の場合）・・・（４）
但し、（３）式及び（４）式において、Ｋ（Ｃ）は、異種物質充填部が配置された領域を通過するときの凝固シェルの凝固係数（ｍｍ／ｍｉｎ０．５）、Ｋ（Ｏ）は、異種物質充填部が配置されていない領域を通過するときの凝固シェルの凝固係数（ｍｍ／ｍｉｎ０．５）である。 The solidification coefficient of the solidified shell when passing through the region where the foreign substance filling portion is disposed and the solidification coefficient of the solidified shell when passing through the region where the foreign material filling portion is not disposed are the following (3 The method for continuous casting of steel according to any one of claims 1 to 4, wherein the formula (4) or the formula (4) is satisfied.
0.6 ≦ K (C) / K (O) ≦ 0.95 (provided that K (C) <K (O)) (3)
0.6 ≦ K (O) / K (C) ≦ 0.95 (provided that K (C)> K (O)) (4)
However, in the formulas (3) and (4), K (C) is the solidification coefficient (mm / min 0.5 ) of the solidified shell when passing through the region where the dissimilar substance filling portion is arranged, K (O ) Is a solidification coefficient (mm / min 0.5 ) of the solidified shell when passing through a region where the different substance filling portion is not disposed.
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