WO2021002130A1 - Manufacturing method for high-cleanliness steel - Google Patents

Manufacturing method for high-cleanliness steel Download PDF

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Publication number
WO2021002130A1
WO2021002130A1 PCT/JP2020/021579 JP2020021579W WO2021002130A1 WO 2021002130 A1 WO2021002130 A1 WO 2021002130A1 JP 2020021579 W JP2020021579 W JP 2020021579W WO 2021002130 A1 WO2021002130 A1 WO 2021002130A1
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tundish
gas
inert gas
region
blown
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PCT/JP2020/021579
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French (fr)
Japanese (ja)
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村井 剛
南 雄介
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Jfeスチール株式会社
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Priority to CN202080047262.7A priority Critical patent/CN114025897B/en
Priority to JP2020544298A priority patent/JP6784349B1/en
Publication of WO2021002130A1 publication Critical patent/WO2021002130A1/en

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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B22CASTING; POWDER METALLURGY
    • B22DCASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/10Supplying or treating molten metal
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B22CASTING; POWDER METALLURGY
    • B22DCASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/10Supplying or treating molten metal
    • B22D11/106Shielding the molten jet
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B22CASTING; POWDER METALLURGY
    • B22DCASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/10Supplying or treating molten metal
    • B22D11/11Treating the molten metal
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B22CASTING; POWDER METALLURGY
    • B22DCASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/16Controlling or regulating processes or operations
    • B22D11/18Controlling or regulating processes or operations for pouring

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  • the present invention relates to a method for producing highly clean steel by efficiently replacing the atmosphere inside the tundish with an inert gas when continuously casting steel.
  • a long nozzle attached to the bottom of the ladle is used when injecting molten steel from the ladle into the tundish. Then, by immersing the tip in the molten steel in the tundish, the injected molten steel is shielded from the air and flux is added on the molten steel in the tundish to prevent oxidation. However, since the tip of the long nozzle is not immersed in the molten steel in the tundish at the start of injection of molten steel from the ladle into the tundish, the molten steel is exposed to air and undergoes reoxidation in which it is oxidized.
  • Patent Document 1 states that the space between the tundish and the lid is completely reduced in order to reduce the oxygen concentration in the tundish before injection.
  • a method of introducing Ar gas into the tundish while sealing is disclosed.
  • the inner diameter of the nozzle for blowing the inert gas into the tundish is set to 40 mm or more, and the penetration depth of the nozzle into the tundish is secured to be 1/4 or more of the tundish depth.
  • a method of reducing the gas flow velocity at the time of blowing to prevent air entrainment is disclosed.
  • the method described in Patent Document 1 has a problem that a space for inserting a molten steel injection nozzle is required in the tundish lid in order to inject molten steel into the tundish. Further, considering the thermal deformation of the tundish lid and the tundish body, there is a problem that it is difficult to completely seal the tundish. When the inert gas is blown into the tundish by the method described in Patent Document 1 in a situation where the tundish cannot be sealed, air is entrained through the injection point and the gap of the tundish lid, and the substitution of the inert gas is insufficient. The problem arises.
  • the present invention has been made in view of such circumstances, and reoxidation of the molten steel in the tundish by air, which is the main cause of reducing the cleanliness of the molten steel at the start of injection of the molten steel into the tundish, is performed.
  • the inventors have found that the atmosphere in the tundish can be efficiently replaced by controlling the flow velocity and the depth of the inert gas to be blown, and the gas flow in the tundish, and have developed the present invention.
  • the method for producing high-clean steel of the present invention which advantageously solves the above problems, is a method for preventing reoxidation of molten steel by creating a non-oxidizing atmosphere in the tundish before injecting molten steel into the tundish when continuously casting steel.
  • the present invention is characterized in that an inert gas heavier than air is blown toward the bottom of the tundish under the conditions satisfying the following equations (1) and (2).
  • the method for producing high-clean steel according to the present invention is as follows.
  • the inert gas is blown into the tundish from one or more nozzles, the inert gas is blown into each of the nozzles under the condition satisfying the following equation (3).
  • Q 1 + Q 2 + ... + Q n Q ...
  • Q n the amount of gas blown from the nth nozzle (Nm 3 / s)
  • H n Height (m) from the bottom of the tundish of the nth nozzle to the bottom of the gas blowing nozzle
  • d n Gas blowing nozzle inner diameter (m) of the nth nozzle
  • n Represents an integer greater than or equal to 1.
  • the tundish has a weir for controlling the flow of molten steel, and each of the tundish regions divided by the weir is set as a separate gas blowing region, and one or more gas blowing nozzles are provided in each region. Is provided, and the inert gas is blown into each region under the conditions satisfying the above equations (1) and (2) or the above equations (1) to (3). Can be a more preferred solution.
  • the boundary of the "divided tundish area" is the position of the upper end of the weir.
  • the atmosphere inside the tundish is quickly and efficiently replaced with an inert gas before the molten steel is injected from the ladle into the tundish.
  • the oxygen concentration of the injected molten steel is reduced, and the reoxidation of the injected molten steel by air is suppressed. Therefore, it is possible to suppress the amount of non-metal inclusions produced, and it is possible to produce highly clean steel.
  • FIG. 1 It is a schematic diagram of the tundish used in one embodiment of the present invention, and shows (a) a cross-sectional view and (b) a perspective view. It is a schematic diagram of the tundish used in another embodiment of the present invention, and shows (a) a sectional view and (b) a perspective view. It is a schematic diagram which shows the cross section of the tundish used in Example 1.
  • FIG. 2 It is a schematic diagram which shows the cross section of the tundish used in Example 2.
  • FIG. 3 It is a schematic diagram which shows the cross section of the tundish used in Example 3.
  • the inventors thought as follows. When continuously casting steel, it is effective to prevent reoxidation of the molten steel by creating a non-oxidizing atmosphere in the tundish before injecting the molten steel into the tundish.
  • the non-oxidizing atmosphere preferably has an oxygen concentration of 2.0 vol% or less, and more preferably 1.0 vol% or less.
  • it is effective to replace the air in the tundish with an inert gas. Therefore, in order to efficiently replace the air in the tundish with the inert gas, it is necessary to control the flow velocity and depth of the Blow-in inert gas, and the gas flow in the tundish. I thought.
  • the inert gas was made heavier than air, and the direction in which the gas was blown was set toward the bottom of the tundish. This is because the bottom of the tundish is gradually replaced with an inert gas.
  • the inert gas heavier than air include Ar gas, carbon dioxide gas, a mixed gas thereof, and a gas in which nitrogen is partially mixed.
  • Re 4 ⁇ ⁇ ⁇ Q / ( ⁇ ⁇ P) ⁇ ⁇ ⁇ (5)
  • Inert gas density (kg / m 3 )
  • Q Amount of inert gas blown (Nm 3 / s)
  • Inert gas viscosity (Pa ⁇ s)
  • P Representative length (m)
  • the flow changes from laminar flow to turbulent flow when the Re number is 2000 to 4000.
  • the oxygen concentration in the tundish was measured by changing the amount of the inert gas blown in
  • the inventors measured the representative length P as the peripheral length PTD (m) of the gas replacement region, that is, the upper surface of the tundish. It has been found that when the number of Res exceeds 2000 when the circumference is set, the oxygen concentration is less likely to decrease as compared with the case where the number of Res exceeds 2000 or less. As a result, the following equation (1) was obtained. 4 ⁇ ⁇ ⁇ Q / ( ⁇ ⁇ P TD ) ⁇ 2000 ⁇ ⁇ ⁇ (1)
  • the flow velocity of the gas to be blown the effect of the flow velocity when the gas collides with the bottom of the tundish was examined. If the flow velocity of the gas when it collides with the bottom is too large, it collides with the bottom and becomes a reverse flow, and the flow flows out to the upper part of the tundish. Therefore, there is a possibility that the entire tundish cannot be replaced efficiently due to the formation of a stagnant portion or the suction of air from the gap between the tundish and the lid. On the other hand, if the flow velocity of the gas is too small, the inert gas may not spread to every corner of the bottom of the tundish and may not be completely replaced. Therefore, it was considered that there is an appropriate value for the flow velocity when colliding with the bottom.
  • A ( ⁇ / 4) ⁇ (2Htan ( ⁇ ) + d) 2 ... (6)
  • H height (m) from the bottom of the tundish to the lower end of the gas blowing nozzle
  • Spread angle (°) of blown gas
  • d Gas blowing nozzle inner diameter (m)
  • the spread angle ⁇ of the blown gas was set to 12 °, which is generally said.
  • the average gas flow velocity v (m / s) when a gas having a flow rate q (Nm 3 / s) collides with the region A of the atmospheric temperature T (K) is determined by the following (6) in consideration of the above equation (6). It is expressed by equation 7).
  • the nozzle diameter and height conditions for gas blowing can be expressed by the following equation (8).
  • the average gas flow velocity v is less than 5 m / s, the gas flow rate may be too small and it may take too much time to replace the gas in the tundish.
  • it exceeds 20 m / s turbulence may occur. 5 ⁇ q ⁇ T / ⁇ 74.5 ⁇ (2Htan (12 °) + d) 2 ⁇ ⁇ 20 ⁇ ⁇ ⁇ (8)
  • Q n the amount of gas blown from the nth nozzle (Nm 3 / s)
  • H n Height (m) from the bottom of the tundish of the nth nozzle to the bottom of the gas blowing nozzle
  • d n Gas blowing nozzle inner diameter (m) of the nth nozzle
  • n Represents an integer greater than or equal to 1.
  • the amount Q of the inert gas that is heavier than the air blown into the tundish is replaced with gas so as to satisfy the above equation (1).
  • Highly clean steel can be manufactured by adjusting the circumference of the region to be PTD according to the PTD.
  • the nozzle height H n , the nozzle inner diameter d n , and the gas blowing are so as to satisfy the above equation (3). It is more preferable to adjust the amount Q n .
  • the tundish has a weir for adjusting the flow
  • gas is blown into each of the tundish regions divided by the position of the upper end of the weir as a boundary, so that the gas replacement of the atmosphere inside the tundish is more even. It is preferable because it is performed in. At that time, it is preferable that the above equations (1) and (2), or the above equations (1) to (3) are satisfied for each tundish region.
  • FIG. 1 and 2 are schematic views of an apparatus used in a method for carrying out the present invention (hereinafter referred to as the present method), which are (a) a schematic cross-sectional view and (b) a perspective view, respectively.
  • reference numeral 1 denotes a tundish body, in which a nozzle 2 for supplying molten steel to two continuous casting molds (not shown) is arranged, and a dipping nozzle 4 is attached to a lower portion thereof via a sliding nozzle 3.
  • the tundish main body 1 is covered with a lid 5, and an opening 6 for a long nozzle is installed in the central portion of the lid 5.
  • burner openings 7 for preheating the tundish body 1 are provided on both sides of the lid 5 with the opening 6 interposed therebetween.
  • FIG. 1 shows a state after the burner (not shown) is inserted through the burner opening 7 to preheat the tundish main body 1.
  • the broken line in FIG. 1B shows the inner method of the upper surface of the tundish, where L represents the length and W represents the width. Circumferential length P TD of the above-described gas replacement region can be calculated by 2L + 2W.
  • the gas blowing nozzle 8 is inserted into the tundish main body 1 through the openings 6 and 7 of the tundish lid 5.
  • the number, inner diameter, and installation height of the gas blowing nozzles 8 are not particularly limited as long as the above equations (1) and (2), preferably equation (3) are satisfied, and a plurality of nozzles 8 are used. When blowing, it is not necessary that the conditions for blowing are the same for each nozzle.
  • FIG. 2 when the weir 9 is installed in the tundish main body 1, it is preferable to install the gas blowing nozzle 8 in each of the regions divided by the weir 9.
  • the height of the weir 9, the shape of the openings, the shape such as the number, and the installation position are not particularly limited.
  • Broken line in FIG. 2 (b) shows the clear width of the tundish top
  • two-dot chain line in FIG. 2 (a) shows the boundaries of the divided regions the position of the upper end of the weir as a boundary
  • L 1 , L 2 represent the length of each of the region 1 and the region 2
  • W represents the width thereof.
  • the circumference P TD1 of the gas replacement region 1 described above can be calculated by 2L 1 + 2W, and the circumference P TD2 of the gas replacement region 2 can be calculated by 2L 2 + 2W.
  • each region needs to satisfy the above equations (1) and (2), preferably equation (3).
  • the gas blowing nozzle 8 is inserted into the tundish body 1 after the preheating is completed through the opening of the lid 5. At that time, the sliding nozzle 3 is closed. Further, it does not matter whether or not the immersion nozzle 4 is attached.
  • the gas When the gas is blown, it may be blown at a constant flow rate from the start to the end of the blow, and if the above equations (1) and (2), preferably the equation (3) are satisfied, for example, from the start of replacement of the atmosphere.
  • the flow rate may be changed stepwise or continuously until the end.
  • the gas blowing nozzle 8 When the predetermined gas flow rate has been blown, the gas blowing nozzle 8 is discharged, and if the immersion nozzle 4 is not installed, it is installed, and it is longer in the tundish body 1 than the ladle containing the smelted molten steel. The molten steel is injected through the nozzle. At the same time, the sliding nozzle 3 is opened and continuous casting is started.
  • Ar gas is an inert gas having a higher density than air.
  • Table 1 shows the number of nozzles 8, the inner diameter, the installation height, the Ar gas blowing amount, and the blowing time. Under the conditions satisfying the equations (1) and (2) (treatments Nos. 1 to 3 and 6 in Table 1), the oxygen concentration in the tundish 1 can be set to 2.0 vol% or less, and (1) to (3).
  • the oxygen concentration in the tundish 1 could be 1.0 vol% or less.
  • the oxygen concentration in Tundish 1 exceeded 2.0 vol%.
  • the number of oxides in steel from the casting start position to the slab 2 m position is measured, the target number of oxides is set to 1.0, and the ratio of the number of oxides in the slab to that is the index of bottom slab cleanliness. It was shown to. As a result, in the example of the present invention, the number of oxides could be lower than that of the comparative example. As described above, it was found that the gas replacement in the tundish can be effectively performed by this method.
  • the non-injection side region including the mold molten steel supply nozzle 2 was designated as a tundish region 1 (Zone 1), and the region on the injection side from the ladle was designated as a tundish region 2 (Zone 2).
  • the left and right regions 1 on FIG. 4 are plane-symmetrical and have the same volume and the same peripheral length.
  • Tables 2-1 and 2 show the volumes V 1 , V 2 , and the peripheral lengths P TD 1 and P TD 2 of each region. After the lid 5 was put on the tundish lid 5, Ar gas was blown from the gas blowing nozzle 8 installed in the opening 6 for the long nozzle and the opening 7 for the burner of the tundish lid 5. Tables 2-1 and 2 show the number of nozzles 8, the inner diameter, the installation height, the amount of Ar gas blown, and the blowing time. Table 2-3 shows the evaluation results of the atmospheric oxygen concentration in the tundish after gas replacement and the cleanliness of the bottom slab. Under the conditions satisfying the equations (1) to (3) in all the regions (treatments No.
  • the oxygen concentration in the tundish 1 could be 1.0 vol% or less.
  • the oxygen concentration in the tundish 1 can be set to 2.0 vol% or less under the conditions (Tables 2-1 to 3 in Treatment Nos. 8 to 11) that satisfy the equations (1) and (2) in all regions. It was.
  • the number of oxides in the steel at the position 2 m from the casting start position is measured, the target number of oxides is 1.0, and the ratio of the number of oxides in the slab to that is the index of bottom slab cleanliness. Shown in 3. As a result, in the example of the present invention, the number of oxides could be lower than that of the comparative example. It was found that the gas replacement in the tundish was effectively performed by this method.
  • the non-injection side region including the mold molten steel supply nozzle 2 was designated as a tundish region 1 (Zone 1), and the region on the injection side from the ladle was designated as a tundish region 2 (Zone 2).
  • the left and right regions 1 on FIG. 5 are plane-symmetrical and have the same volume and the same peripheral length.
  • Tables 3-1 and 2 show the volumes V 1 , V 2 , and the peripheral lengths P TD 1 and P TD 2 of each region.
  • Table 3-3 shows the evaluation results of the atmospheric oxygen concentration in the tundish after gas replacement and the cleanliness of the bottom slab. After the lid 5 was put on the tundish lid 5, Ar gas was blown from the gas blowing nozzle 8 installed in the opening 6 for the long nozzle and the opening 7 for the burner of the tundish lid 5.
  • Tables 3-1 and 2 show the number of nozzles 8, the inner diameter, the installation height, the amount of Ar gas blown, and the blowing time. Under the conditions that satisfy the equations (1) and (2) in all regions (treatment Nos.
  • the number of oxides in steel at the position 2 m from the casting start position is measured, the target number of oxides is set to 1.0, and the ratio of the number of oxides in bloom to that is shown in Table 3 as an index of bottom slab cleanliness. Indicated. As a result, in the example of the present invention, the number of oxides could be lower than that of the comparative example. It was found that the gas replacement in the tundish was effectively performed by this method.
  • the present invention is not limited to the above-exemplified examples, and when continuously casting steel, the atmosphere can be quickly and efficiently replaced with an inert gas before the start of injecting molten steel into the tundish. It is suitable for application to the production of. This method can be applied not only to tundish but also to devices or methods that require gas replacement of the atmosphere.

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Abstract

Provided is a manufacturing method for a high-cleanliness steel, wherein, in continuous casting of steel, a non-oxidizing atmosphere is formed in a tundish before a molten steel is poured into the tundish to prevent reoxidation of the molten steel. The manufacturing method is characterized in that an inert gas that is heavier than air is blown toward the bottom of the tundish under conditions satisfying expressions (1) and (2). (In the expressions, ρ represents the density (kg/m3) of the inert gas; Q represents the total blow-in amount (Nm3/s) of the inert gas; μ represents the viscosity (Pa·s) of the inert gas; PTD represents the peripheral length (m) of a gas replacement region; V represents the volume (m3) of a gas blow-in region; T represents the atmospheric temperature (K) in the tundish; and tmax represents the gas blowable time (s).) (1): 4⋅ρ⋅Q/(μ⋅PTD) ≤ 2000 (2): 3(V/Q)/(T/298) ≤ tmax

Description

高清浄鋼の製造方法Highly clean steel manufacturing method
 本発明は、鋼を連続鋳造するに際し、タンディッシュ内雰囲気を不活性ガスで効率よく置換して高清浄鋼を製造する方法に関するものである。 The present invention relates to a method for producing highly clean steel by efficiently replacing the atmosphere inside the tundish with an inert gas when continuously casting steel.
 鋼を連続鋳造するに際し、取鍋からタンディッシュへの溶鋼注入時には取鍋の下部に取り付けられたロングノズルを用いている。そして、その先端をタンディッシュ内の溶鋼に浸漬した状態とすることによって注入溶鋼を空気から遮断するとともにタンディッシュ内の溶鋼上にフラックスを添加して酸化を防止している。しかし、取鍋からタンディッシュへの溶鋼注入開始時にはロングノズルの先端部がタンディッシュ内の溶鋼中に浸漬されていないため、溶鋼は空気にさらされて酸化する再酸化が起こる。 When continuously casting steel, a long nozzle attached to the bottom of the ladle is used when injecting molten steel from the ladle into the tundish. Then, by immersing the tip in the molten steel in the tundish, the injected molten steel is shielded from the air and flux is added on the molten steel in the tundish to prevent oxidation. However, since the tip of the long nozzle is not immersed in the molten steel in the tundish at the start of injection of molten steel from the ladle into the tundish, the molten steel is exposed to air and undergoes reoxidation in which it is oxidized.
 このような取鍋からタンディッシュへの溶鋼注入開始時での再酸化による生成酸化物、すなわち非金属介在物が連続鋳造鋳片中に捕捉されると、その鋳片から製造された鋼板で表面疵などの欠陥の原因となる。従って、取鍋からタンディッシュへの溶鋼注入開始時に非金属介在物を低減させることが課題になっており、従来から種々の再酸化防止策が提案されている。 When oxides produced by reoxidation at the start of injection of molten steel from such a ladle into a tundish, that is, non-metal inclusions, are trapped in a continuously cast slab, they are surfaced by a steel plate produced from the slab. It causes defects such as flaws. Therefore, it has become an issue to reduce non-metal inclusions at the start of molten steel injection from the ladle to the tundish, and various anti-oxidation measures have been conventionally proposed.
 取鍋からタンディッシュへの溶鋼注入開始時の再酸化防止策としては、例えば、特許文献1には、注入する前にタンディッシュ内の酸素濃度を下げるべく、タンディッシュと蓋の間を完全に密閉するとともに、タンディッシュ内にArガスを導入する方法が開示されている。また、特許文献2には、タンディッシュ内に不活性ガスを吹き込むノズルの内径を40mm以上とし、且つノズルのタンディッシュ内への進入深さをタンディッシュ深さの1/4以上確保することで、吹き込み時のガス流速を低減して、空気の巻き込みを防止する方法が開示されている。  As a measure to prevent reoxidation at the start of molten steel injection from the ladle to the tundish, for example, Patent Document 1 states that the space between the tundish and the lid is completely reduced in order to reduce the oxygen concentration in the tundish before injection. A method of introducing Ar gas into the tundish while sealing is disclosed. Further, in Patent Document 2, the inner diameter of the nozzle for blowing the inert gas into the tundish is set to 40 mm or more, and the penetration depth of the nozzle into the tundish is secured to be 1/4 or more of the tundish depth. , A method of reducing the gas flow velocity at the time of blowing to prevent air entrainment is disclosed.
特開昭63-188460号報JP-A-63-188460 特開平 9-168846号報Japanese Patent Application Laid-Open No. 9-168846
 しかしながら、特許文献1に記載の方法は、タンディッシュ内に溶鋼を注入するために、タンディッシュ蓋に溶鋼注入用ノズルを挿入できる空間を必要とする問題があった。さらにタンディッシュ蓋およびタンディッシュ本体の熱変形まで考慮するとタンディッシュを完全に密閉することが難しいという問題があった。タンディッシュが密閉できない状況で特許文献1に記載の方法を用いてタンディッシュ内へ不活性ガスを吹き込むと、注入点やタンディッシュ蓋の隙間から空気を巻き込み、不活性ガスの置換が不十分となるといった問題が生じる。また、特許文献2に記載の方法では、吹き込むガスの流量が変われば流速も変わるため、タンディッシュの容量やガス吹き込みの可能な時間によっては不活性ガスによる置換が十分に行われないという問題がある。 However, the method described in Patent Document 1 has a problem that a space for inserting a molten steel injection nozzle is required in the tundish lid in order to inject molten steel into the tundish. Further, considering the thermal deformation of the tundish lid and the tundish body, there is a problem that it is difficult to completely seal the tundish. When the inert gas is blown into the tundish by the method described in Patent Document 1 in a situation where the tundish cannot be sealed, air is entrained through the injection point and the gap of the tundish lid, and the substitution of the inert gas is insufficient. The problem arises. Further, in the method described in Patent Document 2, since the flow velocity changes as the flow rate of the blown gas changes, there is a problem that the replacement with the inert gas is not sufficiently performed depending on the capacity of the tundish and the time during which the gas can be blown. is there.
 本発明は、このような事情に鑑みてなされたものであって、タンディッシュ内への溶鋼注入開始時に溶鋼の清浄性を低下させる主原因となっているタンディッシュ内溶鋼の空気による再酸化を防止するために、タンディッシュの容量等の条件に依らずタンディッシュ内雰囲気の酸素濃度を迅速に、かつ効率的に低減して高清浄鋼を製造する方法を提案することを目的とする。 The present invention has been made in view of such circumstances, and reoxidation of the molten steel in the tundish by air, which is the main cause of reducing the cleanliness of the molten steel at the start of injection of the molten steel into the tundish, is performed. In order to prevent this, it is an object of the present invention to propose a method for producing highly clean steel by rapidly and efficiently reducing the oxygen concentration in the atmosphere inside the tundish regardless of the conditions such as the capacity of the tundish.
 発明者らは、吹き込む不活性ガスの流速と吹き込む深さ、さらにはタンディッシュ内でのガスの流れを制御することで効率的にタンディッシュ内雰囲気が置換できることを見出し、本発明を開発した。上記課題を有利に解決する本発明の高清浄鋼の製造方法は、鋼を連続鋳造するに際し、タンディッシュへの溶鋼注入前にタンディッシュ内を無酸化雰囲気にして溶鋼の再酸化を防止する方法において、下記(1)および(2)式を満たす条件でタンディッシュ底部へ向かって、空気より重い不活性ガスを吹き込むことを特徴とする。
 4・ρ・Q/(μ・PTD)≦2000  ・・・(1)
 3(V/Q)/(T/298)≦tmax  ・・・(2)
ここで、ρ:不活性ガス密度(kg/m)、
    Q:不活性ガス総吹き込み量(Nm/s)、
    μ:不活性ガス粘度(Pa・s)、
    PTD:ガス置換領域周長さ(m)、
    V:ガス吹き込み領域体積(m)、
    T:タンディッシュ内雰囲気温度(K)、
    tmax:ガス吹き込み可能時間(s)、
を表す。
The inventors have found that the atmosphere in the tundish can be efficiently replaced by controlling the flow velocity and the depth of the inert gas to be blown, and the gas flow in the tundish, and have developed the present invention. The method for producing high-clean steel of the present invention, which advantageously solves the above problems, is a method for preventing reoxidation of molten steel by creating a non-oxidizing atmosphere in the tundish before injecting molten steel into the tundish when continuously casting steel. The present invention is characterized in that an inert gas heavier than air is blown toward the bottom of the tundish under the conditions satisfying the following equations (1) and (2).
4 ・ ρ ・ Q / (μ ・ P TD ) ≦ 2000 ・ ・ ・ (1)
3 (V / Q) / (T / 298) ≤ t max ... (2)
Here, ρ: Inert gas density (kg / m 3 ),
Q: Total amount of inert gas blown (Nm 3 / s),
μ: Inert gas viscosity (Pa · s),
PTD : Perimeter of gas replacement region (m),
V: Gas blowing area volume (m 3 ),
T: Atmospheric temperature inside the tundish (K),
t max : Gas blowing time (s),
Represents.
 なお、本発明にかかる高清浄鋼の製造方法は、
前記不活性ガスをタンディッシュ内に1または2以上のノズルから吹き込む際に、該ノズル各々について下記(3)式を満たす条件で前記不活性ガスを吹き込むこと、
がより好ましい解決手段になり得るものと考えられる。
 5≦Q・T/{74.5π(2Htan(12°)+d}≦20  ・・・(3)
 Q+Q+・・・・+Q=Q  ・・・(4)
ここで、Q:n番目のノズルからのガス吹き込み量(Nm/s)、
    H:n番目のノズルのタンディッシュ底部からガス吹き込みノズル下端までの高さ(m)、
    d:n番目のノズルのガス吹き込みノズル内径(m)、
    n :1以上の整数
を表す。
The method for producing high-clean steel according to the present invention is as follows.
When the inert gas is blown into the tundish from one or more nozzles, the inert gas is blown into each of the nozzles under the condition satisfying the following equation (3).
Can be a more preferred solution.
5 ≦ Q n・ T / {74.5π (2H n tan (12 °) + d n ) 2 } ≦ 20 ・ ・ ・ (3)
Q 1 + Q 2 + ... + Q n = Q ... (4)
Here, Q n : the amount of gas blown from the nth nozzle (Nm 3 / s),
H n : Height (m) from the bottom of the tundish of the nth nozzle to the bottom of the gas blowing nozzle,
d n : Gas blowing nozzle inner diameter (m) of the nth nozzle,
n: Represents an integer greater than or equal to 1.
 また、本発明にかかる高清浄鋼の製造方法は、
前記タンディッシュは、溶鋼の流動を制御するための堰を有しており、堰で分割されたタンディッシュ領域それぞれを別々のガス吹込み領域として、それぞれの領域に1つ以上のガス吹込みノズルを設け、それぞれの領域ごとに前記(1)および(2)式、または、前記(1)~(3)式を満たす条件で不活性ガスを吹き込むこと、
がより好ましい解決手段になり得るものと考えられる。ここで、「分割されたタンディッシュ領域」の境界は、堰の上端の位置とする。
Further, the method for producing high-clean steel according to the present invention is:
The tundish has a weir for controlling the flow of molten steel, and each of the tundish regions divided by the weir is set as a separate gas blowing region, and one or more gas blowing nozzles are provided in each region. Is provided, and the inert gas is blown into each region under the conditions satisfying the above equations (1) and (2) or the above equations (1) to (3).
Can be a more preferred solution. Here, the boundary of the "divided tundish area" is the position of the upper end of the weir.
 本発明によれば、鋼を連続鋳造するに際し、取鍋からタンディッシュへ溶鋼を注入する前にタンディッシュ内雰囲気を不活性ガスで迅速に、かつ効率的に置換することで、タンディッシュ内雰囲気の酸素濃度を低減し、注入された溶鋼の空気による再酸化が抑制される。よって、非金属介在物の生成量を抑制することが可能となり、高清浄鋼を製造することができる。 According to the present invention, when continuously casting steel, the atmosphere inside the tundish is quickly and efficiently replaced with an inert gas before the molten steel is injected from the ladle into the tundish. The oxygen concentration of the injected molten steel is reduced, and the reoxidation of the injected molten steel by air is suppressed. Therefore, it is possible to suppress the amount of non-metal inclusions produced, and it is possible to produce highly clean steel.
本発明の一実施形態に用いるタンディッシュの模式図であり、(a)断面図および(b)斜視図を示す。It is a schematic diagram of the tundish used in one embodiment of the present invention, and shows (a) a cross-sectional view and (b) a perspective view. 本発明の他の実施形態に用いるタンディッシュの模式図であり、(a)断面図および(b)斜視図を示す。It is a schematic diagram of the tundish used in another embodiment of the present invention, and shows (a) a sectional view and (b) a perspective view. 実施例1に用いるタンディッシュの断面を示す模式図である。It is a schematic diagram which shows the cross section of the tundish used in Example 1. FIG. 実施例2に用いるタンディッシュの断面を示す模式図である。It is a schematic diagram which shows the cross section of the tundish used in Example 2. 実施例3に用いるタンディッシュの断面を示す模式図である。It is a schematic diagram which shows the cross section of the tundish used in Example 3.
 発明者らは、課題を解決するに当たり、以下のように考えた。
 鋼を連続鋳造するに際し、タンディッシュへの溶鋼注入前にタンディッシュ内を無酸化雰囲気にして溶鋼の再酸化を防止することが有効である。ここで、無酸化雰囲気とは、酸素濃度が2.0vol%以下が好ましく、1.0vol%以下がさらに好ましい。タンディッシュ内を無酸化雰囲気にするには、タンディッシュ内の空気を不活性ガスで置換することが有効である。そこで、タンディッシュ内の空気の不活性ガスでの置換を効率的に行うためには、吹き込む不活性ガスの流速と吹き込む深さ、さらにはタンディッシュ内でのガスの流れを制御する必要があると考えた。まず、不活性ガスは空気より重いものとし、ガスを吹き込む方向については、タンディッシュの底部に向かう方向とした。これは、タンディッシュの底部から徐々に不活性ガスで置換していくためである。また、タンディッシュ内のガスの流動が乱流になってしまうと、タンディッシュ内雰囲気と外気の混合が促進してしまうと考え、乱流にならない条件を選ぶこととした。なお、空気より重い不活性ガスは、例えば、Arガスや二酸化炭素ガス、その混合ガスや、さらには一部窒素を混合したガスが挙げられる。
In solving the problem, the inventors thought as follows.
When continuously casting steel, it is effective to prevent reoxidation of the molten steel by creating a non-oxidizing atmosphere in the tundish before injecting the molten steel into the tundish. Here, the non-oxidizing atmosphere preferably has an oxygen concentration of 2.0 vol% or less, and more preferably 1.0 vol% or less. In order to create a non-oxidizing atmosphere in the tundish, it is effective to replace the air in the tundish with an inert gas. Therefore, in order to efficiently replace the air in the tundish with the inert gas, it is necessary to control the flow velocity and depth of the Blow-in inert gas, and the gas flow in the tundish. I thought. First, the inert gas was made heavier than air, and the direction in which the gas was blown was set toward the bottom of the tundish. This is because the bottom of the tundish is gradually replaced with an inert gas. In addition, considering that if the gas flow in the tundish becomes turbulent, the mixing of the atmosphere inside the tundish and the outside air will be promoted, so we decided to select the conditions that do not cause turbulence. Examples of the inert gas heavier than air include Ar gas, carbon dioxide gas, a mixed gas thereof, and a gas in which nitrogen is partially mixed.
 ここで、タンディッシュ内のガスの流動を評価するため、Re数(レイノルズ数)を用いることとした。Re数は下記(5)式で表される。
 Re=4・ρ・Q/(μ・P)  ・・・(5)
ここで、ρ:不活性ガス密度(kg/m)、
    Q:不活性ガス吹き込み量(Nm/s)、
    μ:不活性ガス粘度(Pa・s)、
    P:代表長さ(m)、
を表す。
Here, in order to evaluate the flow of gas in the tundish, it was decided to use the Re number (Reynolds number). The Re number is expressed by the following equation (5).
Re = 4 ・ ρ ・ Q / (μ ・ P) ・ ・ ・ (5)
Here, ρ: Inert gas density (kg / m 3 ),
Q: Amount of inert gas blown (Nm 3 / s),
μ: Inert gas viscosity (Pa · s),
P: Representative length (m),
Represents.
 一般的に、流動が層流から乱流に変わるのはRe数が2000~4000の時と言われている。発明者らは、不活性ガスの吹き込み量を変えて、タンディッシュ内の酸素濃度を測定したところ、代表長さPをガス置換領域の周長さPTD(m)、すなわちタンディッシュの上面部周囲長としたときのRe数が2000を超えると2000以下の場合に比較して、酸素濃度が低下しにくくなることを見出した。これにより、下記(1)式を得た。
 4・ρ・Q/(μ・PTD)≦2000  ・・・(1)
Generally, it is said that the flow changes from laminar flow to turbulent flow when the Re number is 2000 to 4000. When the oxygen concentration in the tundish was measured by changing the amount of the inert gas blown in, the inventors measured the representative length P as the peripheral length PTD (m) of the gas replacement region, that is, the upper surface of the tundish. It has been found that when the number of Res exceeds 2000 when the circumference is set, the oxygen concentration is less likely to decrease as compared with the case where the number of Res exceeds 2000 or less. As a result, the following equation (1) was obtained.
4 ・ ρ ・ Q / (μ ・ P TD ) ≦ 2000 ・ ・ ・ (1)
 次に、鋳造開始前にタンディッシュ内を不活性ガスで置換できる時間には、操業上限りがあるため、その時間内に置換が完了するガス量を吹き込む必要があると考えた。完全混合モデルでは、容積の3倍のガス量が必要である。また、タンディッシュは予熱しているため、その内部で吹き込んだガスは膨張することから、完全置換に必要なガス流量Q(Nm/s)は下記(2)式で表される。
 3(V/Q)/(T/298)≦tmax  ・・・(2)
ここで、V:ガス吹き込み領域の体積(m)、
    T:タンディッシュ内の雰囲気温度(K)、
    tmax:ガス吹き込み可能時間(s)、
を表す。
Next, since the time during which the inside of the tundish can be replaced with the inert gas before the start of casting is limited in terms of operation, it is considered necessary to inject the amount of gas for which the replacement is completed within that time. The fully mixed model requires three times the volume of gas. Further, since the tundish is preheated, the gas blown into the tundish expands, so the gas flow rate Q (Nm 3 / s) required for complete replacement is expressed by the following equation (2).
3 (V / Q) / (T / 298) ≤ t max ... (2)
Here, V: the volume of the gas blowing region (m 3 ),
T: Atmospheric temperature (K) in the tundish,
t max : Gas blowing time (s),
Represents.
 さらに、吹き込むガスの流速について、ガスがタンディッシュの底部に衝突する際の流速の影響を検討した。底部に衝突する際のガスの流速が大きすぎると、底部に衝突して反転流となり、タンディッシュ上部へ抜けていく流れとなる。そのため、滞留部ができたり、タンディッシュと蓋の隙間から空気の吸い込みが発生したりして、タンディッシュ全体を効率よく置換できないおそれがある。一方で、ガスの流速が小さすぎると、タンディッシュ底部隅々に不活性ガスが行き渡らず、置換しきれなくなるとおそれがある。そこで、底部に衝突する際の流速には適正値があると考えた。しかしながら、底部に衝突する際のガス流速の測定は困難なため、ガス流量とガス吹き込みノズルの内径、タンディッシュ底部からの距離により、タンディッシュ底部に到達するガス流速を算出することとした。 Furthermore, regarding the flow velocity of the gas to be blown, the effect of the flow velocity when the gas collides with the bottom of the tundish was examined. If the flow velocity of the gas when it collides with the bottom is too large, it collides with the bottom and becomes a reverse flow, and the flow flows out to the upper part of the tundish. Therefore, there is a possibility that the entire tundish cannot be replaced efficiently due to the formation of a stagnant portion or the suction of air from the gap between the tundish and the lid. On the other hand, if the flow velocity of the gas is too small, the inert gas may not spread to every corner of the bottom of the tundish and may not be completely replaced. Therefore, it was considered that there is an appropriate value for the flow velocity when colliding with the bottom. However, since it is difficult to measure the gas flow velocity when colliding with the bottom, it was decided to calculate the gas flow velocity reaching the bottom of the tundish from the gas flow rate, the inner diameter of the gas blowing nozzle, and the distance from the bottom of the tundish.
 タンディッシュ底部にガスが衝突する領域の面積A(m)は下記(6)式で表される。
 A=(π/4)×(2Htan(θ)+d)  ・・・(6)
ここで、H:タンディッシュ底部からガス吹き込みノズル下端までの高さ(m)、
    θ:吹き込みガスの広がり角度(°)、
    d:ガス吹き込みノズル内径(m)、
を表す。
The area A (m 2 ) of the region where the gas collides with the bottom of the tundish is expressed by the following equation (6).
A = (π / 4) × (2Htan (θ) + d) 2 ... (6)
Here, H: height (m) from the bottom of the tundish to the lower end of the gas blowing nozzle,
θ: Spread angle (°) of blown gas,
d: Gas blowing nozzle inner diameter (m),
Represents.
 ここで、吹き込みガスの広がり角度θを一般的に言われている12°とした。また、雰囲気温度T(K)の領域Aに流量q(Nm/s)のガスが衝突した場合の平均ガス流速v(m/s)は、上記(6)式を考慮して、下記(7)式で表される。
 v=q・(T/298)/A
  =q・T/{74.5π(2Htan(12°)+d)}  ・・・(7)
Here, the spread angle θ of the blown gas was set to 12 °, which is generally said. Further, the average gas flow velocity v (m / s) when a gas having a flow rate q (Nm 3 / s) collides with the region A of the atmospheric temperature T (K) is determined by the following (6) in consideration of the above equation (6). It is expressed by equation 7).
v = q · (T / 298) / A
= Q · T / {74.5π (2Htan (12 °) + d) 2 } ・ ・ ・ (7)
 ここで、種々の条件を変えて、容器内のガス置換の測定を行ったところ、平均ガス流速vが5~20m/sの範囲であれば、効率的にガス置換を行えることが分かった。そのため、ガス吹き込みのためのノズル径、高さ条件は下記(8)式で表すことができる。ここで、平均ガス流速vが5m/s未満では、ガス流量が少なすぎて、タンディッシュ内のガス置換に時間がかかりすぎるおそれがある。一方、20m/s超えでは、乱流となるおそれがある。
 5≦q・T/{74.5π(2Htan(12°)+d)}≦20  ・・・(8)
Here, when the gas replacement in the container was measured under various conditions, it was found that the gas replacement can be efficiently performed if the average gas flow velocity v is in the range of 5 to 20 m / s. Therefore, the nozzle diameter and height conditions for gas blowing can be expressed by the following equation (8). Here, if the average gas flow velocity v is less than 5 m / s, the gas flow rate may be too small and it may take too much time to replace the gas in the tundish. On the other hand, if it exceeds 20 m / s, turbulence may occur.
5 ≦ q ・ T / {74.5π (2Htan (12 °) + d) 2 } ≦ 20 ・ ・ ・ (8)
 ガス吹き込み位置が1または2以上の場合はそれぞれの位置で上記(8)式を満たす必要があり、そのガス吹込み個所からのガス吹き込み流量の合計が、ガス総吹き込み流量Q(Nm/s)となるため、(8)式は、下記(3)および(4)式で表せる。
 5≦Q×T/{74.5π(2Htan(12°)+d}≦20  ・・・(3)
 Q+Q+・・・・+Q=Q  ・・・(4)
ここで、Q:n番目のノズルからのガス吹き込み量(Nm/s)、
    H:n番目のノズルのタンディッシュ底部からガス吹き込みノズル下端までの高さ(m)、
    d:n番目のノズルのガス吹き込みノズル内径(m)、
    n :1以上の整数
を表す。
When the gas blowing position is 1 or 2 or more, it is necessary to satisfy the above equation (8) at each position, and the total gas blowing flow rate from the gas blowing position is the total gas blowing flow rate Q (Nm 3 / s). ), Therefore, the equation (8) can be expressed by the following equations (3) and (4).
5 ≦ Q n × T / {74.5π (2H n tan (12 °) + d n ) 2 } ≦ 20 ・ ・ ・ (3)
Q 1 + Q 2 + ... + Q n = Q ... (4)
Here, Q n : the amount of gas blown from the nth nozzle (Nm 3 / s),
H n : Height (m) from the bottom of the tundish of the nth nozzle to the bottom of the gas blowing nozzle,
d n : Gas blowing nozzle inner diameter (m) of the nth nozzle,
n: Represents an integer greater than or equal to 1.
 したがって、タンディッシュ内を無酸化雰囲気にして溶鋼の再酸化を防止するにあたっては、タンディッシュ内へ吹き込む空気より重い不活性ガスの吹き込み量Qを、上記(1)式を満足するようにガス置換する領域の周長さPTDに応じて調整することで高清浄鋼を製造できる。また、上記(2)式を満足するように、ガス吹き込み可能な時間tmaxに応じて、ガス吹き込み量Qを調整する必要がある。また、1または2以上のノズルを用いてガスを吹き込む場合には、上記(3)式を満足するように、それぞれのノズルごとにガスを吹き込むノズル高さHとノズル内径d、ガス吹き込み量Qを調整することがより好ましい。さらに、タンディッシュが流動調整用の堰を有している場合は、堰の上端の位置を境界として分割されたタンディッシュ領域それぞれにガスを吹き込むことで、タンディッシュ内雰囲気のガス置換がより均等に行われるので好ましい。その際、それぞれのタンディッシュ領域ごとに、上記(1)式および上記(2)式、または、上記(1)~(3)式を満足するようにすることが好ましい。 Therefore, in order to prevent the molten steel from being reoxidized by creating a non-oxidizing atmosphere in the tundish, the amount Q of the inert gas that is heavier than the air blown into the tundish is replaced with gas so as to satisfy the above equation (1). Highly clean steel can be manufactured by adjusting the circumference of the region to be PTD according to the PTD. Further, it is necessary to adjust the gas blowing amount Q according to the gas blowing time t max so as to satisfy the above equation (2). When gas is blown using one or more nozzles, the nozzle height H n , the nozzle inner diameter d n , and the gas blowing are so as to satisfy the above equation (3). It is more preferable to adjust the amount Q n . Furthermore, when the tundish has a weir for adjusting the flow, gas is blown into each of the tundish regions divided by the position of the upper end of the weir as a boundary, so that the gas replacement of the atmosphere inside the tundish is more even. It is preferable because it is performed in. At that time, it is preferable that the above equations (1) and (2), or the above equations (1) to (3) are satisfied for each tundish region.
 以下、本発明を、添付図面を参照して説明する。図1および2は、本発明を実施する方法(以下、本方法という)に用いる装置の模式図であり、それぞれ(a)断面模式図および(b)斜視図である。 Hereinafter, the present invention will be described with reference to the accompanying drawings. 1 and 2 are schematic views of an apparatus used in a method for carrying out the present invention (hereinafter referred to as the present method), which are (a) a schematic cross-sectional view and (b) a perspective view, respectively.
 図1において、1はタンディッシュ本体であり、連続鋳造鋳型(図示せず)2台への溶鋼供給用ノズル2が配置されており、その下部にはスライディングノズル3を介して浸漬ノズル4が取り付けてある。また、タンディッシュ本体1には蓋5がかぶせてあり、この蓋5の中央部にはロングノズル用の開口部6が設置されている。また、図1上で開口部6を挟んで蓋5の両側にタンディッシュ本体1を予熱するためのバーナー用開口部7が設置されている。なお、図1はバーナー用開口部7からバーナー(図示せず)を挿入してタンディッシュ本体1を予熱した後の状態を示している。図1(b)の破線は、タンディッシュ上面の内法を示しており、Lはその長さ、Wはその幅を表す。上述のガス置換領域の周長さPTDは、2L+2Wで計算できる。 In FIG. 1, reference numeral 1 denotes a tundish body, in which a nozzle 2 for supplying molten steel to two continuous casting molds (not shown) is arranged, and a dipping nozzle 4 is attached to a lower portion thereof via a sliding nozzle 3. There is. Further, the tundish main body 1 is covered with a lid 5, and an opening 6 for a long nozzle is installed in the central portion of the lid 5. Further, on FIG. 1, burner openings 7 for preheating the tundish body 1 are provided on both sides of the lid 5 with the opening 6 interposed therebetween. Note that FIG. 1 shows a state after the burner (not shown) is inserted through the burner opening 7 to preheat the tundish main body 1. The broken line in FIG. 1B shows the inner method of the upper surface of the tundish, where L represents the length and W represents the width. Circumferential length P TD of the above-described gas replacement region can be calculated by 2L + 2W.
 また、タンディッシュ本体1にはタンディッシュ蓋5の開口部6、7を介して、ガス吹き込みノズル8が挿入されている。このガス吹き込みノズル8の本数、内径、設置高さについては、上記(1)および(2)式、好ましくは(3)式を満たしていれば特に制限は無いし、複数のノズル8を用いて吹き込むに際しては、ノズルごとに吹き込む条件が同じである必要もない。 Further, the gas blowing nozzle 8 is inserted into the tundish main body 1 through the openings 6 and 7 of the tundish lid 5. The number, inner diameter, and installation height of the gas blowing nozzles 8 are not particularly limited as long as the above equations (1) and (2), preferably equation (3) are satisfied, and a plurality of nozzles 8 are used. When blowing, it is not necessary that the conditions for blowing are the same for each nozzle.
 また、図2に示すように、タンディッシュ本体1に堰9を設置している場合は、堰9で分割された領域それぞれにガス吹き込みノズル8を設置することが好ましい。この堰9については、その高さ、開孔部の形状、数等の形状、設置位置については特に制限は無い。図2(b)の破線は、タンディッシュ上面の内法を示しており、図2(a)の2点鎖線は、堰の上端の位置を境界として分割された領域の境界を示す、L、Lは領域1および領域2それぞれの長さを表し、Wはその幅を表す。上述のガス置換領域1の周長さPTD1は、2L+2Wで計算でき、ガス置換領域2の周長さPTD2は、2L+2Wで計算できる。この場合には、それぞれの領域で、上記(1)および(2)式、好ましくは(3)式を満たしている必要がある。 Further, as shown in FIG. 2, when the weir 9 is installed in the tundish main body 1, it is preferable to install the gas blowing nozzle 8 in each of the regions divided by the weir 9. The height of the weir 9, the shape of the openings, the shape such as the number, and the installation position are not particularly limited. Broken line in FIG. 2 (b) shows the clear width of the tundish top, two-dot chain line in FIG. 2 (a) shows the boundaries of the divided regions the position of the upper end of the weir as a boundary, L 1 , L 2 represent the length of each of the region 1 and the region 2, and W represents the width thereof. The circumference P TD1 of the gas replacement region 1 described above can be calculated by 2L 1 + 2W, and the circumference P TD2 of the gas replacement region 2 can be calculated by 2L 2 + 2W. In this case, each region needs to satisfy the above equations (1) and (2), preferably equation (3).
 次に本方法の操作について説明する。
 予熱完了後のタンディッシュ本体1に蓋5の開口部より、ガス吹き込みノズル8を挿入する。その際、スライディングノズル3は閉止しておく。また、浸漬ノズル4の装着の有無は問わない。
Next, the operation of this method will be described.
The gas blowing nozzle 8 is inserted into the tundish body 1 after the preheating is completed through the opening of the lid 5. At that time, the sliding nozzle 3 is closed. Further, it does not matter whether or not the immersion nozzle 4 is attached.
 ガス吹き込みを行うにあたっては、吹き込み開始から終了まで一定の流量で吹き込んでも良いし、上記(1)および(2)式、好ましくは(3)式を満たすのであれば、例えば、雰囲気の置換開始から終了まで段階的あるいは連続的に流量を変えても良い。 When the gas is blown, it may be blown at a constant flow rate from the start to the end of the blow, and if the above equations (1) and (2), preferably the equation (3) are satisfied, for example, from the start of replacement of the atmosphere. The flow rate may be changed stepwise or continuously until the end.
 所定のガス流量が吹き込み終わったら、ガス吹き込みノズル8を排し、浸漬ノズル4が装着されていなければ装着し、精錬処理を施された溶鋼の収納された取鍋よりタンディッシュ本体1内にロングノズルを介して溶鋼を注入する。それとともに、スライディングノズル3を開けて、連続鋳造を開始する。 When the predetermined gas flow rate has been blown, the gas blowing nozzle 8 is discharged, and if the immersion nozzle 4 is not installed, it is installed, and it is longer in the tundish body 1 than the ladle containing the smelted molten steel. The molten steel is injected through the nozzle. At the same time, the sliding nozzle 3 is opened and continuous casting is started.
 以上の方法を用いタンディッシュ内を無酸化雰囲気に制御することで、再酸化による介在物の生成を抑制し、清浄度の高い鋼を得ることができる。 By controlling the inside of the tundish to a non-oxidizing atmosphere using the above method, it is possible to suppress the formation of inclusions due to reoxidation and obtain steel with high cleanliness.
<実施例1>
 図3に示すように、容量30tの1ストランド連続鋳造機用タンディッシュ1(内部体積V=5.8m、周囲長さPTD=10.5m、雰囲気温度T=873K)に蓋5をした上で、タンディッシュ蓋5のロングノズル用の開口部6に設置したガス吹き込みノズル8からArガスを吹き込んだ。Arガスは空気より密度の大きい不活性ガスである。ノズル8の本数、内径、設置高さ、Arガス吹き込み量、吹き込み時間を表1に示す。(1)および(2)式を満たす条件(表1中処理No.1~3および6)ではタンディッシュ1内酸素濃度を2.0vol%以下にすることができ、(1)~(3)式を満たす条件(表1中処理No.1~3)ではタンディッシュ1内酸素濃度を1.0vol%以下にすることができた。対して、(1)および(2)式のどちらかでも満たしていない条件(表1中処理No.4、5および7)ではタンディッシュ1内酸素濃度は2.0vol%超えであった。上記の条件で、C=0.03%の低炭素鋼の鋳造を行った。鋳造開始位置からスラブ2m位置までの鋼中酸化物個数を測定し、目標とする酸化物個数を1.0として、それとスラブ中酸化物の個数の比をボトム鋳片清浄度の指数で表1に示した。その結果、本発明例では比較例に対して酸化物個数を低位にできた。以上、本方法によりタンディッシュ内ガス置換が有効に行なえていることがわかった。
<Example 1>
As shown in FIG. 3, capacity 30t of 1 strand continuous casting machine tundish 1 (inner volume V = 5.8 m 3, perimeter P TD = 10.5 m, the ambient temperature T = 873 K) the lid 5 and Above, Ar gas was blown from the gas blowing nozzle 8 installed in the opening 6 for the long nozzle of the tundish lid 5. Ar gas is an inert gas having a higher density than air. Table 1 shows the number of nozzles 8, the inner diameter, the installation height, the Ar gas blowing amount, and the blowing time. Under the conditions satisfying the equations (1) and (2) (treatments Nos. 1 to 3 and 6 in Table 1), the oxygen concentration in the tundish 1 can be set to 2.0 vol% or less, and (1) to (3). Under the conditions satisfying the formula (treatments Nos. 1 to 3 in Table 1), the oxygen concentration in the tundish 1 could be 1.0 vol% or less. On the other hand, under the condition that neither of the equations (1) and (2) was satisfied (treatments Nos. 4, 5 and 7 in Table 1), the oxygen concentration in Tundish 1 exceeded 2.0 vol%. Under the above conditions, low carbon steel with C = 0.03% was cast. The number of oxides in steel from the casting start position to the slab 2 m position is measured, the target number of oxides is set to 1.0, and the ratio of the number of oxides in the slab to that is the index of bottom slab cleanliness. It was shown to. As a result, in the example of the present invention, the number of oxides could be lower than that of the comparative example. As described above, it was found that the gas replacement in the tundish can be effectively performed by this method.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
<実施例2>
 図4に示すように、容量70tの2ストランド連続鋳造機用タンディッシュ1(内部体積V=12.3m、周囲長さPTD=19.3m、雰囲気温度T=923K)に堰9を設置し、取鍋からの注入側と非注入側の領域に分割した。鋳型溶鋼供給ノズル2を含む非注入側の領域をタンディッシュ領域1(Zone1)とし、取鍋からの注入側の領域をタンディッシュ領域2(Zone2)とした。図4上で左右の領域1は、面対称で、同一体積、同一周囲長さを有する。各領域それぞれの体積V、V、周囲長さPTD1、PTD2を表2-1および2に示す。このタンディッシュ1に蓋5をした上で、タンディッシュ蓋5のロングノズル用の開口部6とバーナー用開口部7に設置したガス吹き込みノズル8からArガスを吹き込んだ。ノズル8の本数、内径、設置高さ、Arガス吹き込み量、吹き込み時間を表2-1および2に示す。表2-3にガス置換後のタンディッシュ内の雰囲気酸素濃度とボトム鋳片の清浄度の評価結果を示す。すべての領域で(1)~(3)式を満たす条件(表2-1~3中処理No.8および9)ではタンディッシュ1内酸素濃度を1.0vol%以下にできた。また、すべての領域で(1)および(2)式を満たす条件(表2-1~3中処理No.8~11)ではタンディッシュ1内酸素濃度を2.0vol%以下にすることができた。対して、(1)および(2)式のどちらかでも満たしていない条件の領域がある場合(表2-1~3中処理No.12~14)では、その領域のタンディッシュ1内酸素濃度は2.0vol%超えであった。上記の条件で、C=0.002%の極低炭素鋼の鋳造を行った。鋳造開始位置からスラブ2m位置の鋼中酸化物個数を測定し、目標とする酸化物個数を1.0として、それとスラブ中酸化物の個数の比をボトム鋳片清浄度の指数で表2-3に示した。その結果、本発明例では比較例に対して酸化物個数を低位にできた。本方法によりタンディッシュ内ガス置換が有効に行なえていることがわかった。
<Example 2>
As shown in FIG. 4 installed capacity tundish for 2 strand continuous casting machine 70 t 1 (inner volume V = 12.3 m 3, perimeter P TD = 19.3 m, the ambient temperature T = 923 K) the weir 9 Then, it was divided into an injection side and a non-injection side area from the ladle. The non-injection side region including the mold molten steel supply nozzle 2 was designated as a tundish region 1 (Zone 1), and the region on the injection side from the ladle was designated as a tundish region 2 (Zone 2). The left and right regions 1 on FIG. 4 are plane-symmetrical and have the same volume and the same peripheral length. Tables 2-1 and 2 show the volumes V 1 , V 2 , and the peripheral lengths P TD 1 and P TD 2 of each region. After the lid 5 was put on the tundish lid 5, Ar gas was blown from the gas blowing nozzle 8 installed in the opening 6 for the long nozzle and the opening 7 for the burner of the tundish lid 5. Tables 2-1 and 2 show the number of nozzles 8, the inner diameter, the installation height, the amount of Ar gas blown, and the blowing time. Table 2-3 shows the evaluation results of the atmospheric oxygen concentration in the tundish after gas replacement and the cleanliness of the bottom slab. Under the conditions satisfying the equations (1) to (3) in all the regions (treatments No. 8 and 9 in Tables 2-1 to 3), the oxygen concentration in the tundish 1 could be 1.0 vol% or less. In addition, the oxygen concentration in the tundish 1 can be set to 2.0 vol% or less under the conditions (Tables 2-1 to 3 in Treatment Nos. 8 to 11) that satisfy the equations (1) and (2) in all regions. It was. On the other hand, when there is a region under the condition that neither of the equations (1) and (2) is satisfied (treatment Nos. 12 to 14 in Tables 2-1 to 3), the oxygen concentration in the tundish 1 in that region Was over 2.0 vol%. Under the above conditions, ultra-low carbon steel with C = 0.002% was cast. The number of oxides in the steel at the position 2 m from the casting start position is measured, the target number of oxides is 1.0, and the ratio of the number of oxides in the slab to that is the index of bottom slab cleanliness. Shown in 3. As a result, in the example of the present invention, the number of oxides could be lower than that of the comparative example. It was found that the gas replacement in the tundish was effectively performed by this method.
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000004
Figure JPOXMLDOC01-appb-T000004
<実施例3>
 図5に示すように、容量20tの4ストランド連続鋳造機用タンディッシュ1(内部体積4.4m、周囲長さ16.6m、雰囲気温度T=873K)に堰9を設置し、取鍋からの注入側と非注入側の領域に分割した。鋳型溶鋼供給ノズル2を含む非注入側の領域をタンディッシュ領域1(Zone1)とし、取鍋からの注入側の領域をタンディッシュ領域2(Zone2)とした。図5上で左右の領域1は、面対称で、同一体積、同一周囲長さを有する。各領域それぞれの体積V、V、周囲長さPTD1、PTD2を表3-1および2に示す。表3-3にガス置換後のタンディッシュ内の雰囲気酸素濃度とボトム鋳片の清浄度の評価結果を示す。このタンディッシュ1に蓋5をした上で、タンディッシュ蓋5のロングノズル用の開口部6とバーナー用開口部7に設置したガス吹き込みノズル8からArガスを吹き込んだ。ノズル8の本数、内径、設置高さ、Arガス吹き込み量、吹き込み時間は表3-1および2に示す。すべての領域で(1)および(2)式を満たす条件(表3-1~3中処理No.15~18)ではタンディッシュ1内酸素濃度を全領域で2.0vol%以下にすることができた。また、すべての領域で(1)~(3)式を満たす条件(表3-1~3中処理No.15および16)ではタンディッシュ1内酸素濃度を全領域で1.0%以下にすることができた。対して、式(1)を満たしていない条件の領域がある場合(表3-1~3中処理No.19および20)ではその領域のタンディッシュ1内酸素濃度は2.0vol%超えであった。上記の条件で、C=1.0%の高炭素鋼の鋳造を行った。鋳造開始位置からブルーム2m位置の鋼中酸化物個数を測定し、目標とする酸化物個数を1.0として、それとブルーム中酸化物の個数の比をボトム鋳片清浄度の指数で表3に示した。その結果、本発明例では比較例に対して酸化物個数を低位にできた。本方法によりタンディッシュ内ガス置換が有効に行なえていることがわかった。
<Example 3>
As shown in FIG. 5, a weir 9 is installed in a tundish 1 for a 4-strand continuous casting machine having a capacity of 20 tons (internal volume 4.4 m 3 , peripheral length 16.6 m, atmospheric temperature T = 873 K), and from a ladle. It was divided into the injection side and non-injection side regions. The non-injection side region including the mold molten steel supply nozzle 2 was designated as a tundish region 1 (Zone 1), and the region on the injection side from the ladle was designated as a tundish region 2 (Zone 2). The left and right regions 1 on FIG. 5 are plane-symmetrical and have the same volume and the same peripheral length. Tables 3-1 and 2 show the volumes V 1 , V 2 , and the peripheral lengths P TD 1 and P TD 2 of each region. Table 3-3 shows the evaluation results of the atmospheric oxygen concentration in the tundish after gas replacement and the cleanliness of the bottom slab. After the lid 5 was put on the tundish lid 5, Ar gas was blown from the gas blowing nozzle 8 installed in the opening 6 for the long nozzle and the opening 7 for the burner of the tundish lid 5. Tables 3-1 and 2 show the number of nozzles 8, the inner diameter, the installation height, the amount of Ar gas blown, and the blowing time. Under the conditions that satisfy the equations (1) and (2) in all regions (treatment Nos. 15 to 18 in Tables 3-1 to 3), the oxygen concentration in Tundish 1 can be reduced to 2.0 vol% or less in all regions. did it. Further, under the conditions satisfying the equations (1) to (3) in all regions (treatments No. 15 and 16 in Tables 3-1 to 3), the oxygen concentration in Tundish 1 is set to 1.0% or less in all regions. I was able to. On the other hand, when there is a region under the condition that does not satisfy the formula (1) (treatments Nos. 19 and 20 in Tables 3-1 to 3), the oxygen concentration in the tundish 1 in that region exceeds 2.0 vol%. It was. Under the above conditions, high carbon steel with C = 1.0% was cast. The number of oxides in steel at the position 2 m from the casting start position is measured, the target number of oxides is set to 1.0, and the ratio of the number of oxides in bloom to that is shown in Table 3 as an index of bottom slab cleanliness. Indicated. As a result, in the example of the present invention, the number of oxides could be lower than that of the comparative example. It was found that the gas replacement in the tundish was effectively performed by this method.
Figure JPOXMLDOC01-appb-T000005
Figure JPOXMLDOC01-appb-T000005
Figure JPOXMLDOC01-appb-T000006
Figure JPOXMLDOC01-appb-T000006
Figure JPOXMLDOC01-appb-T000007
Figure JPOXMLDOC01-appb-T000007
 本発明は、上記例示の実施例に限られず、鋼を連続鋳造する際に、タンディッシュ内に溶鋼を注入開始する前に雰囲気を不活性ガスで迅速に、かつ効率よく置換できるので高清浄鋼の製造に適用して好適である。本方法は、タンディッシュ以外にも雰囲気をガス置換する必要のある装置または方法にも適用可能である。 The present invention is not limited to the above-exemplified examples, and when continuously casting steel, the atmosphere can be quickly and efficiently replaced with an inert gas before the start of injecting molten steel into the tundish. It is suitable for application to the production of. This method can be applied not only to tundish but also to devices or methods that require gas replacement of the atmosphere.
 1 タンディッシュ
 2 溶鋼供給用ノズル
 3 スライディングノズル
 4 浸漬ノズル
 5 蓋
 6 ロングノズル用開口部
 7 バーナー用開口部
 8 ガス吹き込みノズル
 9 堰
Zone1 タンディッシュ領域1
Zone2 タンディッシュ領域2
1 Tandish 2 Nozzle for supplying molten steel 3 Sliding nozzle 4 Immersion nozzle 5 Lid 6 Opening for long nozzle 7 Opening for burner 8 Gas blowing nozzle 9 Weir Zone1 Tandish area 1
Zone2 Tandish area 2

Claims (4)

  1. 鋼を連続鋳造するに際し、タンディッシュへの溶鋼注入前にタンディッシュ内を無酸化雰囲気にして溶鋼の再酸化を防止する方法において、下記(1)および(2)式を満たす条件でタンディッシュ底部へ向かって、空気より重い不活性ガスを吹き込むことを特徴とする高清浄鋼の製造方法。
     4・ρ・Q/(μ・PTD)≦2000  ・・・(1)
     3(V/Q)/(T/298)≦tmax  ・・・(2)
    ここで、ρ:不活性ガスの密度(kg/m)、
        Q:不活性ガスの総吹き込み量(Nm/s)、
        μ:不活性ガス粘度(Pa・s)、
        PTD:ガス置換領域周長さ(m)、
        V:ガス吹き込み領域体積(m)、
        T:タンディッシュ内雰囲気温度(K)、
        tmax:ガス吹き込み可能時間(s)、
    を表す。
    In the method of continuously casting steel, in a method of preventing the reoxidation of the molten steel by creating a non-oxidizing atmosphere in the tundish before injecting the molten steel into the tundish, the bottom of the tundish under the conditions satisfying the following equations (1) and (2). A method for producing highly clean steel, which comprises blowing an inert gas heavier than air toward the steel.
    4 ・ ρ ・ Q / (μ ・ P TD ) ≦ 2000 ・ ・ ・ (1)
    3 (V / Q) / (T / 298) ≤ t max ... (2)
    Here, ρ: density of the inert gas (kg / m 3 ),
    Q: Total amount of inert gas blown (Nm 3 / s),
    μ: Inert gas viscosity (Pa · s),
    PTD : Perimeter of gas replacement region (m),
    V: Gas blowing area volume (m 3 ),
    T: Atmospheric temperature inside the tundish (K),
    t max : Gas blowing time (s),
    Represents.
  2. 前記不活性ガスをタンディッシュ内に1または2以上のノズルから吹き込む際に、該ノズル各々について下記(3)式を満たす条件で前記不活性ガスを吹き込むことを特徴とする請求項1に記載の高清浄鋼の製造方法。
     5≦Q・T/{74.5π(2Htan(12°)+d}≦20  ・・・(3)
     Q+Q+・・・・+Q=Q  ・・・(4)
    ここで、Q:n番目のノズルからのガス吹き込み量(Nm/s)、
        H:n番目のノズルのタンディッシュ底部からガス吹き込みノズル下端までの高さ(m)、
        d:n番目のノズルのガス吹き込みノズル内径(m)、
        n :1以上の整数
    を表す。
    The first aspect of claim 1, wherein when the inert gas is blown into the tundish from one or more nozzles, the inert gas is blown into each of the nozzles under the condition satisfying the following equation (3). Manufacturing method of highly clean steel.
    5 ≦ Q n・ T / {74.5π (2H n tan (12 °) + d n ) 2 } ≦ 20 ・ ・ ・ (3)
    Q 1 + Q 2 + ... + Q n = Q ... (4)
    Here, Q n : the amount of gas blown from the nth nozzle (Nm 3 / s),
    H n : Height (m) from the bottom of the tundish of the nth nozzle to the bottom of the gas blowing nozzle,
    d n : Gas blowing nozzle inner diameter (m) of the nth nozzle,
    n: Represents an integer greater than or equal to 1.
  3. 前記タンディッシュは、溶鋼の流動を制御するための堰を有しており、堰で分割されたタンディッシュ領域それぞれを別々のガス吹込み領域として、それぞれの領域に1つ以上のガス吹込みノズルを設け、それぞれの領域ごとに前記(1)および(2)式を満たす条件で不活性ガスを吹き込むことを特徴とする請求項1に記載の高清浄鋼の製造方法。 The tundish has a weir for controlling the flow of molten steel, and each of the tundish regions divided by the weir is used as a separate gas blowing region, and one or more gas blowing nozzles are provided in each region. The method for producing highly clean steel according to claim 1, wherein an inert gas is blown into each region under the conditions satisfying the above equations (1) and (2).
  4. 前記タンディッシュは、溶鋼の流動を制御するための堰を有しており、堰で分割されたタンディッシュ領域それぞれを別々のガス吹込み領域として、それぞれの領域に1つ以上のガス吹込みノズルを設け、それぞれの領域ごとに前記(1)~(3)式を満たす条件で不活性ガスを吹き込むことを特徴とする請求項2に記載の高清浄鋼の製造方法。 The tundish has a weir for controlling the flow of molten steel, and each of the tundish regions divided by the weir is used as a separate gas blowing region, and one or more gas blowing nozzles are provided in each region. The method for producing high-clean steel according to claim 2, wherein the inert gas is blown into each region under the conditions satisfying the above equations (1) to (3).
PCT/JP2020/021579 2019-07-01 2020-06-01 Manufacturing method for high-cleanliness steel WO2021002130A1 (en)

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS58112639A (en) * 1981-12-28 1983-07-05 Nippon Steel Corp Charging method for molten metal in continuous casting
JPH09300050A (en) * 1996-05-16 1997-11-25 Nippon Steel Corp Method for cleaning molten steel in tundish
WO2013190799A1 (en) * 2012-06-18 2013-12-27 Jfeスチール株式会社 Method for manufacturing high-purity steel casting, and tundish
JP2016182612A (en) * 2015-03-25 2016-10-20 株式会社神戸製鋼所 Continuous casting method blowing inert gas from upper porous refractory and lower porous refractory

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS58112639A (en) * 1981-12-28 1983-07-05 Nippon Steel Corp Charging method for molten metal in continuous casting
JPH09300050A (en) * 1996-05-16 1997-11-25 Nippon Steel Corp Method for cleaning molten steel in tundish
WO2013190799A1 (en) * 2012-06-18 2013-12-27 Jfeスチール株式会社 Method for manufacturing high-purity steel casting, and tundish
JP2016182612A (en) * 2015-03-25 2016-10-20 株式会社神戸製鋼所 Continuous casting method blowing inert gas from upper porous refractory and lower porous refractory

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