JP4272577B2 - Steel continuous casting method - Google Patents
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- JP4272577B2 JP4272577B2 JP2004116489A JP2004116489A JP4272577B2 JP 4272577 B2 JP4272577 B2 JP 4272577B2 JP 2004116489 A JP2004116489 A JP 2004116489A JP 2004116489 A JP2004116489 A JP 2004116489A JP 4272577 B2 JP4272577 B2 JP 4272577B2
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- 229910000831 Steel Inorganic materials 0.000 title claims description 19
- 238000000034 method Methods 0.000 title claims description 19
- 239000010959 steel Substances 0.000 title claims description 19
- 238000009749 continuous casting Methods 0.000 title claims description 13
- 238000005266 casting Methods 0.000 claims description 41
- 239000000843 powder Substances 0.000 claims description 39
- 229910004298 SiO 2 Inorganic materials 0.000 claims description 25
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 23
- 229910052802 copper Inorganic materials 0.000 claims description 23
- 239000010949 copper Substances 0.000 claims description 23
- 229910000954 Medium-carbon steel Inorganic materials 0.000 claims description 6
- 150000002222 fluorine compounds Chemical class 0.000 claims description 6
- 229910018072 Al 2 O 3 Inorganic materials 0.000 claims description 5
- 230000004907 flux Effects 0.000 description 16
- 230000000694 effects Effects 0.000 description 13
- 239000000203 mixture Substances 0.000 description 13
- 239000000498 cooling water Substances 0.000 description 7
- 238000001816 cooling Methods 0.000 description 6
- 239000000126 substance Substances 0.000 description 6
- 230000005499 meniscus Effects 0.000 description 5
- 238000010583 slow cooling Methods 0.000 description 5
- 239000013078 crystal Substances 0.000 description 4
- 239000002436 steel type Substances 0.000 description 4
- 238000002425 crystallisation Methods 0.000 description 3
- 230000008025 crystallization Effects 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 238000006243 chemical reaction Methods 0.000 description 2
- 238000005336 cracking Methods 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 230000003647 oxidation Effects 0.000 description 2
- 238000007254 oxidation reaction Methods 0.000 description 2
- 230000002265 prevention Effects 0.000 description 2
- 238000007711 solidification Methods 0.000 description 2
- 230000008023 solidification Effects 0.000 description 2
- 229910001208 Crucible steel Inorganic materials 0.000 description 1
- 229910018068 Li 2 O Inorganic materials 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 239000007791 liquid phase Substances 0.000 description 1
- 238000005461 lubrication Methods 0.000 description 1
- CPLXHLVBOLITMK-UHFFFAOYSA-N magnesium oxide Inorganic materials [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 description 1
- 239000000155 melt Substances 0.000 description 1
- 230000000704 physical effect Effects 0.000 description 1
- 229910052708 sodium Inorganic materials 0.000 description 1
- 238000009628 steelmaking Methods 0.000 description 1
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Description
本発明は、銅製鋳型内の溶鋼表面にモールドパウダーを添加して鋳片を連続鋳造するに際して、銅製鋳型の厚みの変動に応じて、モールドパウダーの塩基度や鋳造速度を適切に制御することによって、縦割れやブレークアウト等の問題を生じることなく、安定して操業できるような鋼の連続鋳造方法に関するものである。 By adding mold powder to the surface of molten steel in a copper mold and continuously casting a slab, the present invention appropriately controls the basicity and casting speed of the mold powder according to the variation in the thickness of the copper mold. The present invention relates to a continuous casting method of steel that can be stably operated without causing problems such as vertical cracks and breakouts.
鋼の連続鋳造においては、タンデッシュ内の溶鋼を水冷鋳型内に投入してこれを冷却しつつ（一次冷却）、下方に引き抜かれて更に鋳片表面が冷却されて（二次冷却）鋳片として連続的に製造されるのが一般的である。 In continuous casting of steel, molten steel in the tundish is put into a water-cooled mold and cooled (primary cooling), and drawn downward to further cool the slab surface (secondary cooling) as a slab It is common to produce continuously.
こうした連続鋳造で使用する鋳型は銅製であるのが一般的であるが、製造される鋳片の表面品質を良好に維持するためには、鋳型内での冷却が効果的に行われる必要がある。また、鋳片表面の性状を良好に維持するためには、鋳型内での抜熱量（熱流束）も鋼種に応じて適切に調整する必要がある。 The mold used in such continuous casting is generally made of copper. However, in order to maintain the surface quality of the slab to be manufactured well, it is necessary to effectively cool the mold in the mold. . Moreover, in order to maintain the property of the slab surface satisfactorily, it is necessary to appropriately adjust the heat removal amount (heat flux) in the mold according to the steel type.
上記熱流束は、鋳型厚みや鋳型内冷却水速等によっても大きく変化し、鋳片表面品質に大きな影響を与えることが知られている。特に、中炭素鋼のように包晶反応を伴う鋼材では、熱流束が大きくなると、初期凝固殻の冷却不均一が原因して鋳片表面の縦割れが生じ易くなることが知られている。こうした不都合を解消するには、熱流束をできるだけ小さくする（以下、これを「緩冷却」と呼ぶことがある）ことが有効であることが知られている。例えば、縦割れが生じやすい中炭素鋼（Ｃ含有量：０．０８〜０．２％程度）を対象としたときには、鋳型による抜熱量は、メニスカス下４０ｍｍの位置で３．０ＭＷ／ｍ２程度とすることが縦割れ回避に有効であることが知られている（例えば、非特許文献１）。 It is known that the heat flux varies greatly depending on the mold thickness, the cooling water speed in the mold, and the like, and has a great influence on the slab surface quality. In particular, it is known that in a steel material with a peritectic reaction such as medium carbon steel, when the heat flux increases, vertical cracks on the surface of the slab are likely to occur due to uneven cooling of the initial solidified shell. In order to eliminate such inconvenience, it is known that it is effective to make the heat flux as small as possible (hereinafter, this may be referred to as “slow cooling”). For example, when medium carbon steel (C content: about 0.08 to 0.2%) that tends to cause vertical cracks is targeted, the heat removal by the mold is about 3.0 MW / m 2 at a position 40 mm below the meniscus. Is known to be effective in avoiding vertical cracks (for example, Non-Patent Document 1).
しかしながら、熱流束を制御するにしても、実際の鋳型厚みは使用初期と使用末期では損耗、手入れ等によって変動するものであり、他の条件（例えば鋳型冷却水量）が一定であれば、鋳型厚みによってメニスカス付近での熱流束に大きな差が生じ、これが必然的に鋳片表面品質に多大な影響を及ぼすことがある。 However, even if the heat flux is controlled, the actual mold thickness varies due to wear, care, etc. at the beginning and end of use, and if other conditions (for example, the amount of mold cooling water) are constant, the mold thickness Causes a large difference in the heat flux near the meniscus, which inevitably has a significant impact on the slab surface quality.
一方、連続鋳造を行うに際しては、モールドパウダーを使用することが一般的である。こうしたモールドパウダーは、（１）溶鋼表面の保温や酸化防止、（２）鋳型／初期凝固シェル間の潤滑性確保、（３）均一冷却などの効果を発揮するものである。このモールドパウダーの特性は、鋳片表面性状や安定操業に影響を及ぼし、特にその塩基度［ＣａＯとＳｉＯ２の含有量の比：（ＣａＯ／ＳｉＯ２）］はカスピディンの結晶晶出を通じて鋳型／溶鋼間の熱流束に大きな影響を及ぼすことが知られている。 On the other hand, when performing continuous casting, it is common to use mold powder. Such mold powder exhibits effects such as (1) heat retention and oxidation prevention on the surface of molten steel, (2) ensuring lubricity between the mold and the initial solidified shell, and (3) uniform cooling. Characteristics of the mold powder has an effect on the cast slab surface quality and stable operation, especially [ratio of CaO and SiO 2 content: (CaO / SiO 2)] the basicity mold through crystal crystallization Kasupidin / It is known to have a great influence on the heat flux between molten steel.
例えば、特許文献１には、モールドパウダーの塩基度や結晶化温度を適切に規定することによって、鋳片の表面性状を良好にする技術が提案されている。またこの技術では、モールドパウダーにおける所定温度での粘性を適切に制御することも開示されている。また同様の観点から、モールドパウダーの塩基度に応じて粘性を制御する技術も提案されている（例えば、特許文献２）。 For example, Patent Document 1 proposes a technique for improving the surface properties of a slab by appropriately defining the basicity and crystallization temperature of a mold powder. This technique also discloses appropriately controlling the viscosity of the mold powder at a predetermined temperature. From the same viewpoint, a technique for controlling the viscosity according to the basicity of the mold powder has also been proposed (for example, Patent Document 2).
これらの技術からすれば、モールドパウダーの組成を適切にして塩基度や粘性を制御することは、緩冷却にとって有効に作用するものと考えられる。しかしながら、こうしたモールドパウダーの組成や物性の制御だけでは、鋳片の表面性状が良好にならない場合がある。例えば、鋳造速度の違いや対象とする鋼材の種類によっても、適切なモールドパウダー組成［従って、塩基度（ＣａＯ／ＳｉＯ２）］も異なってくるものであり、こうした条件も適切に考慮しなければ、表面性状に優れた鋳片を安定して製造することができない。 From these techniques, it is considered that controlling the basicity and viscosity by appropriately adjusting the composition of the mold powder works effectively for slow cooling. However, the surface properties of the slab may not be improved only by controlling the composition and physical properties of the mold powder. For example, the appropriate mold powder composition [and thus the basicity (CaO / SiO 2 )] also varies depending on the difference in casting speed and the type of steel material, and these conditions must be properly considered. It is impossible to stably produce a slab excellent in surface properties.
鋳片の種類に応じて塩基度を制御する技術として、例えば特許文献３には、鋳片の化学成分と塩基度との関係を規定することによって、鋳片の縦割れの防止を図る技術も提案されている。 As a technique for controlling basicity in accordance with the type of slab, for example, Patent Document 3 also discloses a technique for preventing vertical cracking of a slab by defining the relationship between the chemical composition of the slab and basicity. Proposed.
しかしながら、上記熱流束については、銅製鋳型の厚み等によっても変化するものであり、この厚みが変動する状況の下では、こうした技術においても適切な操業条件を確立することは困難である。
本発明はこうした従来技術における課題を解決する為になされたものであって、その目的は、鋳型厚みが変動する状況下であっても、鋳型／溶鋼間の適切な熱流速を確保するように制御することによって、縦割れ等が生じないような表面品質の良好な鋳片を得るための連続鋳造方法を提供することにある。 The present invention has been made to solve such problems in the prior art, and its purpose is to ensure an appropriate heat flow rate between the mold and the molten steel even under conditions where the mold thickness varies. It is an object of the present invention to provide a continuous casting method for obtaining a slab having good surface quality so that vertical cracks and the like do not occur by controlling.
上記課題を解決することのできた本発明方法とは、銅製鋳型内の溶鋼表面にモールドパウダーを添加して鋳片を連続鋳造するに当たり、ＣａＯ、ＳｉＯ2および弗素化合物を基本成分とし、塩基度（ＣａＯ／ＳｉＯ2）が０．５〜１．５であるモールドパウダーを用いると共に、銅製鋳型厚みをＴ（ｍｍ）、鋳片の鋳造速度をＶｃ（ｍ／ｍｉｍ）としたとき、銅製鋳型厚みＴが１５〜５０ｍｍの範囲内、且つ鋳造速度Ｖｃが０．５〜３．０ｍ／ｍｉｎの範囲内において、銅製鋳型の厚みＴに応じて、下記（１）式の関係を満足するように決定した塩基度（ＣａＯ／ＳｉＯ2）のモールドパウダーおよび鋳造速度で操業する点に要旨を有するものである。
（ＣａＯ／ＳｉＯ2）≧０．５×Ｖｃ−０．０２８×Ｔ＋０．６６…（１）
The method of the present invention that has been able to solve the above-mentioned problem is that when adding mold powder to the surface of molten steel in a copper mold and continuously casting a slab, CaO, SiO 2 and a fluorine compound are used as basic components, and the basicity ( When using a mold powder having a CaO / SiO 2 ) of 0.5 to 1.5, assuming that the copper mold thickness is T (mm) and the casting speed of the slab is Vc (m / mim), the copper mold thickness T Is within the range of 15 to 50 mm and the casting speed Vc is within the range of 0.5 to 3.0 m / min, depending on the thickness T of the copper mold, the relationship of the following formula (1) is determined. It has a gist in that it operates at a mold powder having basicity (CaO / SiO 2 ) and a casting speed.
(CaO / SiO 2 ) ≧ 0.5 × Vc−0.028 × T + 0.66 (1)
本発明方法で用いるモールドパウダーは、ＣａＯ、ＳｉＯ2および弗素化合物を基本成分とするものであるが、更にＡｌ2Ｏ3、ＭｇＯおよびＮａ2Ｏよりなる群から選ばれる１種以上を含有するものであっても良い。 The mold powder used in the method of the present invention contains CaO, SiO 2 and a fluorine compound as basic components, but further contains at least one selected from the group consisting of Al 2 O 3 , MgO and Na 2 O. It may be.
一方、本発明方法において対象とする鋳片は、Ｃを０．０８〜０．２％程度含有する中炭素鋼種であることが好ましく、こうした鋼種を対象としたときにその効果が最も有効に発揮される。 On the other hand, the slab targeted in the method of the present invention is preferably a medium carbon steel type containing about 0.08 to 0.2% of C, and the effect is most effectively exhibited when such a steel type is targeted. Is done.
本発明では、銅製鋳型の厚みの変動に応じて、モールドパウダーの塩基度や鋳造速度を適切に制御するようにしたので、縦割れやブレークアウト等の問題を生じることなく、安定して操業できるような鋼の連続鋳造方法が実現できた。 In the present invention, the basicity of the mold powder and the casting speed are appropriately controlled according to the variation of the thickness of the copper mold, so that stable operation can be performed without causing problems such as vertical cracks and breakouts. Such a continuous casting method of steel could be realized.
本発明者らは、上記目的を達成する為に様々な角度から検討した。その結果、変動する鋳型銅板厚み、モールドパウダーの塩基度および鋳造速度を所定の関係式を満足するように制御すれば、上記目的が達成されることを見出し、本発明を完成した。 The present inventors have studied from various angles in order to achieve the above object. As a result, the inventors have found that the above object can be achieved by controlling the varying mold copper plate thickness, the basicity of the mold powder, and the casting speed so as to satisfy a predetermined relational expression, thereby completing the present invention.
本発明で用いるモールドパウダーは、溶鋼表面を覆うことによって保温および酸化防止等の基本的な作用を発揮するのは勿論であるが、鋳造速度や銅製鋳型厚みに応じてその塩基度を適切に制御することによって、表面性状の良好な鋳片が確保できるのである。但し、この塩基度が０．５よりも小さくなると、初晶がＳｉＯ２の領域に入りやすくなって凝固温度が非常に高くなるので、メニスカス上部の溶融層および鋳片−鋳型間のパウダー液相中に結晶が晶出し、見掛けの粘性が非常に高くなるので、鋳型／初期凝固シェル間の潤滑性を確保できず、安定した操業に支障をきたすことになる。こうしたことから、モールドパウダーの塩基度は少なくとも０．５以上となるように制御することが好ましい。 The mold powder used in the present invention not only exhibits basic functions such as heat retention and oxidation prevention by covering the molten steel surface, but its basicity is appropriately controlled according to the casting speed and copper mold thickness. By doing so, a slab with good surface properties can be secured. However, if this basicity is less than 0.5, the primary crystal easily enters the SiO 2 region and the solidification temperature becomes very high. Therefore, the melt liquid layer above the meniscus and the powder liquid phase between the slab and the mold Crystals crystallize inside and the apparent viscosity becomes very high, so that the lubricity between the mold and the initial solidified shell cannot be ensured, which hinders stable operation. For these reasons, it is preferable to control the basicity of the mold powder to be at least 0.5 or more.
本発明で用いるモールドパウダーはこれまで一般的に用いられているものであればよいが、具体的にはＣａＯ、ＳｉＯ２および弗素化合物を基本成分とするものが挙げられる。このうち弗素化合物は、粘性の調整および緩冷却を目的にカスピディン結晶の晶出という作用を発揮するものであり、通常３〜１２質量％程度で含有される。このモールドパウダーには、必要によってＡｌ２Ｏ３、ＭｇＯおよびＮａ２Ｏよりなる群から選ばれる１種以上を含有することができ、これらの成分は粘性、凝固温度制御という作用を発揮する。但し、これらの成分があまり多くなると潤滑不良、不均一流入となるので、Ａｌ２Ｏ３およびＭｇＯで１０質量％以下、Ｎａ２Ｏで２０質量％以下とすることが好ましい。 The mold powder used in the present invention may be any mold powder that has been generally used so far, and specific examples thereof include those containing CaO, SiO 2 and a fluorine compound as basic components. Of these, the fluorine compound exhibits the effect of crystallization of caspidine crystals for the purpose of adjusting the viscosity and slow cooling, and is usually contained at about 3 to 12% by mass. If necessary, the mold powder can contain one or more selected from the group consisting of Al 2 O 3 , MgO and Na 2 O, and these components exhibit the effects of viscosity and solidification temperature control. However, if these components are excessively large, poor lubrication and non-uniform inflow will occur. Therefore, it is preferable that the content of Al 2 O 3 and MgO is 10% by mass or less and that of Na 2 O is 20% by mass or less.
本発明の連続鋳造を行うときの銅製鋳型の厚みについては、通常１５〜５０ｍｍ程度であるが、この厚みがあまり薄くなると安全性が確保できなくなるので、１５ｍｍ以上であることが好ましい。また、この厚みがあまり厚くなると、冷却水による冷却効果が発揮されなくなるので、５０ｍｍ程度以下であることが好ましい。従って、本発明方法を実施するに際しては、銅製鋳型の厚みはこの範囲内で適用することが望ましい。本発明では、上記の銅製鋳型厚みの範囲内において、鋳造速度や塩基度を適切に制御することによって鋳型における緩冷却を実現し、表面性状に優れた鋳片が得られるのである。 The thickness of the copper mold when performing the continuous casting of the present invention is usually about 15 to 50 mm. However, if this thickness is too thin, safety cannot be ensured, so it is preferably 15 mm or more. Moreover, since the cooling effect by cooling water will not be exhibited when this thickness becomes too thick, it is preferable that it is about 50 mm or less. Therefore, when carrying out the method of the present invention, it is desirable to apply the thickness of the copper mold within this range. In the present invention, by appropriately controlling the casting speed and basicity within the above-mentioned copper mold thickness range, the mold can be slowly cooled, and a slab excellent in surface properties can be obtained.
一方、鋳造速度については、生産性良く操業を行うためには、少なくとも０．５ｍ／ｍｉｎ以上であることが好ましい。この鋳造速度が速くなればなるほど、熱流束が大きくなる傾向を示すことになるが、本発明では鋳造速度に応じて塩基度を高めることによって緩冷却を実現し、表面性状の良好な鋳片が得られることになる。但し、鋳造速度があまり大きくなり過ぎると他の条件を制御しても溶鋼流動によりメニスカスが不安定となる傾向が高いため、３．０ｍ／ｍｉｎ以下とすることが好ましい。 On the other hand, the casting speed is preferably at least 0.5 m / min or more in order to operate with high productivity. As the casting speed increases, the heat flux tends to increase.However, in the present invention, mild cooling is realized by increasing the basicity according to the casting speed, and a slab having a good surface property is obtained. Will be obtained. However, if the casting speed becomes too high, the meniscus tends to become unstable due to the molten steel flow even if other conditions are controlled, so it is preferable that the casting speed be 3.0 m / min or less.
本発明方法において対象とする鋳片は、Ｃを０．０８〜０．２％含有する中炭素鋼種であることが好ましい。即ち、Ｃを０．０８〜０．２％含有する中炭素鋼種では、包晶反応を伴う鋼種であるので、熱流束の変動による影響を受け易く、熱流速が大きくなることによる鋳片表面品質に大きな影響を及ぼすことから、こうした鋼材を対象としたときに本発明の効果は最も顕著に発揮される。こうした鋼種を想定すると、鋳型によって抜熱量メニスカス下４０ｍｍの位置で３．０ＭＷ／ｍ２程度の熱流束となるように前記（１）式を制御することが目標となる。 The slab targeted in the method of the present invention is preferably a medium carbon steel type containing 0.08 to 0.2% of C. That is, the medium carbon steel type containing 0.08 to 0.2% of C is a steel type with a peritectic reaction, so it is easily affected by fluctuations in the heat flux, and the slab surface quality due to an increase in the heat flow rate. Therefore, the effect of the present invention is most remarkably exhibited when such a steel material is used as a target. Assuming such a steel type, the target is to control the equation (1) so that a heat flux of about 3.0 MW / m 2 is obtained at a position 40 mm below the heat removal meniscus by the mold.
以下、本発明を実施例によって更に詳細に説明するが、下記実施例は本発明を限定する性質のものではなく、前・後記の趣旨に徴して設計変更することはいずれも本発明の技術的範囲に含まれるものである。 Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are not intended to limit the present invention, and any design changes in accordance with the gist of the preceding and following descriptions are technical aspects of the present invention. It is included in the range.
実施例１
本発明者らは、下記の化学成分組成の鋼種の鋳片を連続鋳造した。このときの鋳片サイズは断面形状で２１００ｍｍ×２８０ｍｍであり、銅製鋳型厚みは２０ｍｍである。また、鋳型冷却水速は、５〜１２ｍ／ｓの範囲内とした。
Example 1
The present inventors continuously cast steel slabs having the following chemical composition. The slab size at this time is 2100 mm × 280 mm in cross-sectional shape, and the copper mold thickness is 20 mm. Moreover, the mold cooling water speed was set within a range of 5 to 12 m / s.
（鋳片の化学成分組成）
Ｃ：０．０８〜０．２質量％、Ｓｉ：０．１５質量％、Ｍｎ：１．１質量％、
Ｐ：０．０１質量％、Ｓ：０．００３質量％、Ａｌ：０．０２質量％
このとき、下記表1に示す各種のモールドパウダーを使用し、溶鋼の表面を覆った。また、モールドパウダーの塩基度（ＣａＯ／ＳｉＯ２）および鋳造速度を様々な条件に設定して、連続鋳造を行った。
(Chemical composition of slab)
C: 0.08 to 0.2 mass%, Si: 0.15 mass%, Mn: 1.1 mass%,
P: 0.01 mass%, S: 0.003 mass%, Al: 0.02 mass%
At this time, various mold powders shown in Table 1 below were used to cover the surface of the molten steel. Moreover, continuous casting was performed with the basicity (CaO / SiO 2 ) and casting speed of the mold powder set to various conditions.
得られた鋳片について、その鋳片表面性状を下記の基準で評価した。その結果を、フラックスパウダーの組成、操業条件（鋳造速度、塩基度）と共に、下記表１に併記する。尚、表１において、「操業不安定」とは（Ｎｏ．１，９）、鋳造中に焼き付きの生成やブレイクアウト（鋳片の凝固殻が破断する減少）が生じる兆候を示した状態を意味する。また、この結果に基づき、鋳造速度および塩基度が鋳片表面性状（縦割れの有無）に与える影響を図１に示す。 About the obtained slab, the slab surface property was evaluated on the following reference | standard. The results are shown in Table 1 below together with the composition of the flux powder and the operating conditions (casting speed, basicity). In Table 1, “operational instability” (Nos. 1 and 9) means a state in which signs of seizure formation or breakout (reduction in which the solidified shell of the slab breaks) are generated during casting. To do. Moreover, based on this result, the influence which casting speed and basicity have on the slab surface properties (presence of vertical cracks) is shown in FIG.
（鋳片表面性状の評価基準）
□：鋳片１ｍｍ当たりの縦割れの総長さが２０ｍｍ未満
△：鋳片１ｍｍ当たりの縦割れの総長さが２０ｍｍ以上５０ｍｍ未満
■：鋳片１ｍｍ当たりの縦割れの総長さが５０ｍｍ以上
(Evaluation criteria for slab surface properties)
□: Total length of vertical cracks per 1 mm of cast slab is less than 20 mm △: Total length of vertical cracks per 1 mm of cast slab is less than 20 mm and less than 50 mm ■: Total length of vertical cracks per 1 mm of slab is 50 mm or more
次に、鋳型厚さを３０ｍｍとして（鋳型冷却水速については上記と同じ）、上記と同様の実験を行い、上記と同様にして評価した。その結果を、モールドパウダーの組成、操業条件（鋳造速度、塩基度）と共に、下記表２に併記する。また、この結果に基づき、鋳造速度および塩基度が鋳片表面性状（縦割れの有無）に与える影響を図２に示す。 Next, the mold thickness was set to 30 mm (the mold cooling water speed was the same as above), and the same experiment as described above was performed and evaluated in the same manner as described above. The results are shown together with the composition of the mold powder and the operating conditions (casting speed, basicity) in Table 2 below. Moreover, based on this result, the influence which casting speed and basicity have on the slab surface properties (presence of longitudinal cracks) is shown in FIG.
更に、鋳型厚さを４０ｍｍとして（鋳型冷却水速については上記と同じ）、上記と同様の実験を行い、上記と同様にして評価した。その結果を、フラックスパウダーの組成、操業条件（鋳造速度、塩基度）と共に、下記表３に併記する。また、この結果に基づき、鋳造速度および塩基度が鋳片表面性状（縦割れの有無）に与える影響を図３に示す。 Further, the mold thickness was set to 40 mm (the mold cooling water speed was the same as above), and the same experiment as described above was performed and evaluated in the same manner as described above. The results are shown in Table 3 below together with the composition of the flux powder and the operating conditions (casting speed, basicity). Moreover, based on this result, the influence which casting speed and basicity have on the slab surface properties (presence or absence of longitudinal cracks) is shown in FIG.
これらの結果に基づいて、鋳型厚みが２０〜４０ｍｍの夫々の場合における鋳造速度と塩基度が割れ発生に与える影響についてまとめたのが図４である。この図において、各ラインの上部領域は縦割れが発生しない領域であり、下方領域は縦割れが発生している領域であることを示している。 Based on these results, FIG. 4 summarizes the effects of casting speed and basicity on the occurrence of cracks in each case where the mold thickness is 20 to 40 mm. In this figure, the upper region of each line is a region where no vertical cracks are generated, and the lower region is a region where vertical cracks are generated.
この結果から明らかなように、鋳造速度が速くなるほど熱流束が大きくなり、これを小さくするためには、高い塩基度（ＣａＯ／ＳｉＯ２）のモールドパウダーが必要になることが分かる。また、鋳型厚みが薄いほど、鋳造速度が同一であっても熱流束は大きくなるので、塩基度（ＣａＯ／ＳｉＯ２）が高い状態での緩冷却モールドパウダーが必要になることが分かる。 As is apparent from this result, it can be seen that as the casting speed increases, the heat flux increases, and in order to reduce this, a mold powder having a high basicity (CaO / SiO 2 ) is required. Further, it can be seen that the thinner the mold thickness, the greater the heat flux even at the same casting speed, so that a slow cooling mold powder with a high basicity (CaO / SiO 2 ) is required.
これらの結果に基づいて、塩基度（ＣａＯ／ＳｉＯ２）、鋳型厚み（Ｔ）および鋳造速度（Ｖｃ）の関係について求められたのが前記（１）式である。即ち、鋳型厚みＴの変動が生じたとしてもこの式を満足するように、鋳造速度および塩基度を制御することによって、熱流速が３．０ＭＷ／ｍ２程度の良好な緩冷却が達成され、縦割れ等の発生を効果的に防止できることになる。 Based on these results, the relationship of basicity (CaO / SiO 2 ), mold thickness (T) and casting speed (Vc) was obtained from the above formula (1). That is, by controlling the casting speed and basicity so as to satisfy this equation even if the mold thickness T varies, good slow cooling with a heat flow rate of about 3.0 MW / m 2 is achieved, Generation of vertical cracks and the like can be effectively prevented.
実施例２
本発明者らは、下記表４に示す各種のモールドパウダーを使用し、溶鋼の表面を覆った。また、モールドパウダーの塩基度（ＣａＯ／ＳｉＯ２）および鋳造速度を様々な条件に設定して、連続鋳造を行った。このときの鋳片の化学成分組成および鋳片サイズは実施例１と同じである。また銅製鋳型厚みは３０ｍｍとした（鋳型冷却水速：５〜１２ｍ／ｓ）。
Example 2
The inventors used various mold powders shown in Table 4 below to cover the surface of the molten steel. Moreover, continuous casting was performed with the basicity (CaO / SiO 2 ) and casting speed of the mold powder set to various conditions. The chemical composition and slab size of the slab at this time are the same as those in Example 1. The copper mold thickness was 30 mm (mold cooling water speed: 5 to 12 m / s).
得られた鋳片について、その表面性状を実施例１と同様にして評価した。その結果を、フラックスパウダーの組成、操業条件（鋳造速度、塩基度）と共に、下記表４に併記する。またこの結果に基づき、鋳造速度および塩基度が鋳片表面性状（縦割れの有無）に与える影響を図５に示す。 About the obtained slab, the surface property was evaluated in the same manner as in Example 1. The results are shown in Table 4 below together with the composition of the flux powder and the operating conditions (casting speed, basicity). Moreover, based on this result, the influence which casting speed and basicity have on the slab surface properties (presence of longitudinal cracks) is shown in FIG.
この実施例では、モールドパウダー中のＣａＯおよびＳｉＯ２の含有量を増加させ、それ以外の成分（弗素化合物、Ａｌ２Ｏ３、ＭｇＯ、Ｌｉ２Ｏ、Ｎａ２Ｏ等）の含有量を約２１質量％程度にしたものであるが、こうした化学成分組成であっても、前記図２に示した結果と同様の傾向を示していることが分かる。 In this example, the content of CaO and SiO 2 in the mold powder is increased, and the content of other components (fluorine compound, Al 2 O 3 , MgO, Li 2 O, Na 2 O, etc.) is increased to about 21. Although it is about mass%, it turns out that even if it is such a chemical component composition, the tendency similar to the result shown in the said FIG. 2 is shown.
Claims (3)
（ＣａＯ／ＳｉＯ2）≧０．５×Ｖｃ−０．０２８×Ｔ＋０．６６…（１）In continuously casting a slab by adding mold powder to the surface of molten steel in a copper mold, CaO, SiO 2 and a fluorine compound are basic components, and the basicity (CaO / SiO 2 ) is 0.5 to 1.5. When the mold powder thickness is T, the copper mold thickness is T (mm), and the casting speed of the slab is Vc (m / min), the copper mold thickness T is in the range of 15 to 50 mm, and the casting speed Vc is Mold powder and casting of basicity (CaO / SiO 2 ) determined so as to satisfy the relationship of the following formula (1) according to the thickness T of the copper mold within the range of 0.5 to 3.0 m / min. A continuous casting method of steel, characterized by operating at a speed .
(CaO / SiO 2 ) ≧ 0.5 × Vc−0.028 × T + 0.66 (1)
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| JP4527693B2 (en) * | 2006-07-26 | 2010-08-18 | 株式会社神戸製鋼所 | Continuous casting method of high Al steel slab |
| JP5423719B2 (en) * | 2011-03-31 | 2014-02-19 | 新日鐵住金株式会社 | Steel continuous casting method |
| EP2839901B1 (en) | 2012-06-27 | 2016-05-11 | JFE Steel Corporation | Continuous casting mold and method for continuous casting of steel |
| RU2677560C2 (en) | 2014-10-28 | 2019-01-17 | ДжФЕ СТИЛ КОРПОРЕЙШН | Mold for continuous casting machine and continuous casting method for steel |
| EP3488946A4 (en) | 2015-07-22 | 2019-07-03 | JFE Steel Corporation | Continuous casting mold and method for continuous casting of steel |
| JP6394831B2 (en) | 2016-10-19 | 2018-09-26 | Ｊｆｅスチール株式会社 | Continuous casting mold and steel continuous casting method |
| JP6347864B1 (en) | 2017-03-24 | 2018-06-27 | 日新製鋼株式会社 | Method for producing austenitic stainless steel slab |
| JP2019130585A (en) * | 2018-02-02 | 2019-08-08 | 株式会社日本スペリア社 | Flux for solder, solder composition and soldering flux |
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