JP2009006388A - Continuous casting method of steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a continuous casting method capable of reducing generation of a predictive signal for restrictive breakout when continuously casting Si-killed steel having Al content of less than 0.015 mass%. <P>SOLUTION: In the continuous casting method of steel having Al content of less than 0.015 mass%, the water vapor partial pressure in the atmosphere in contact with the powder covering surface inside a continuous casting mold is made lower than the water vapor partial pressure in the air, and the water vapor partial pressure is controlled to not more than 0.02 atm. It is preferable that a shielding plate is provided in a space between the powder covering surface inside the continuous casting mold and the air, and a gas having the water vapor partial pressure of not more than 0.02 atm is introduced inside the shielding plate. This can reduce the generation of bubbles in a powder film flowing in a space between the mold and a solidified shell, and reduce the generation of the predictive signal for the restrictive breakout. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a continuous casting method of steel, and more particularly to a continuous casting method of Si killed steel having an Al content of less than 0.015% by mass.

In continuous casting of steel, powder for continuous casting is added into the mold. The powder for continuous casting melts on the surface of the molten steel in the mold and forms a lubricating film between the mold wall and the solidified shell. Continuous casting powders are almost all used in slabs and large section blooms. This powder plays a role of preventing oxidation of the molten steel surface in the mold, lubrication between the mold and the slab, capturing the floating inclusions, and keeping the temperature of the molten steel surface in the mold. The powder has many management factors such as its melting rate, viscosity, melting point, and alumina absorption capacity, and the optimum powder differs depending on the steel type, casting speed, slab cross-sectional shape, etc., so the selection is extremely important. Conventional powders for continuous casting have used basicity (CaO / SiO ₂ ) in the range of 0.6 to 1.1.

  When high-speed casting or medium carbon steel is cast, vertical cracks are likely to occur on the surface of the slab. In order to prevent the occurrence of this vertical crack, in Patent Document 1, when the heat transfer resistance of the powder film is increased to slowly cool the solidified shell, the thickness of the solidified shell is made more uniform and the surface of the slab is not easily cracked. It is going to be. For this purpose, an invention is described in which the basicity of the powder is increased and the amount of crystals deposited is increased to increase the heat transfer resistance of the powder film. However, when the basicity of the powder composition is increased, slow cooling of the solidified shell is realized, but the flowability of the powder film decreases, and the flow into the gap between the mold and the solidified shell becomes uneven, especially in the case of high-speed casting. However, there is a problem that constraining breakout is likely to occur. Therefore, unless the vertical crack of the slab becomes a problem as in the case of continuous casting of medium carbon steel, a value of about 1.3 or less is adopted as the basicity of the powder for continuous casting.

  In Patent Document 2, when water vapor is present in the atmosphere near the mold when the melted mold powder solidifies, the starting point of crystal nucleation increases in the mold powder and crystals are likely to precipitate. A method is described in which continuous water vapor partial pressure is increased to 0.05 to 0.7 atm.

  Steel produced by continuous casting is usually killed steel, and deoxidation is mainly performed by adding 0.015% by mass or more of Al. On the other hand, the steel may be continuously cast using Si deoxidation with an Al content of less than 0.015 mass% and an Si content of 0.05 mass% or more. The main purpose of this is to increase the austenite crystal grain size by reducing the Al content and prevent intergranular fracture at high temperatures. Hereinafter, such steel is sometimes referred to as Si killed steel.

  In the constraining breakout, the solidified shell adheres to the mold wall and breaks in the vicinity of the meniscus, the fractured portion of the solidified shell moves downward as the casting progresses, and finally the broken portion reaches the lower end of the mold and breaks out. It is to arrive. If a temperature measurement end is installed on the mold wall, the temperature rises unsteadily when passing through the temperature measurement part when the fractured part of the solidified shell moves below the mold, so it is predicted that a breakout will occur can do. If the casting speed is rapidly reduced when the prediction signal is generated, the breakage portion of the solidified shell can be repaired to prevent the occurrence of breakout.

JP 2000-218348 A JP 2001-225152 A Yu Fuwa et al. “Iron and Steel 53 (1963)”, p. 91

  In the continuous casting of Si killed steel having an Al content of less than 0.015% by mass, a phenomenon that a predictive signal for restrictive breakout frequently occurred was observed. When the Al content is 0.010% by mass or less, the frequency of occurrence further increases. Although breakout does not occur, it is necessary to rapidly reduce the casting speed each time a prediction signal is issued, so the casting productivity is reduced and the casting speed rapid reduction part becomes an unsteady part. It can also cause quality degradation. In selecting the powder for continuous casting, powder with a low basicity (basicity B is about 1.0 to 1.2) is selected in order to prioritize the inflow of the powder film. Occurrence is frequent.

  When the mold temperature in the vicinity of the meniscus was measured, compared with Al killed steel and Al-Si killed steel having an Al content of 0.015% by mass or more, in Si killed steel having an Al content of less than 0.015% by mass, It was found that the mold temperature was low. In the amount of heat removed from the solidified shell to the mold in the vicinity of the meniscus, Si killed steel means that the amount of heat removed is low. In addition, regarding the heat removal amount of the entire mold, it was found that the heat removal amount of Si killed steel was lower than that of other varieties. Despite not using a high basicity powder that slowly cools the heat removal, the heat removal is low, which results in frequent occurrence of constraining breakout prediction signals.

  An object of the present invention is to provide a continuous casting method capable of reducing the generation of a predictive signal of a constraining breakout when continuously casting Si killed steel having an Al content of less than 0.015% by mass.

  As described above, when continuously casting Si killed steel having an Al content of less than 0.015% by mass, the amount of heat removed from the solidified shell to the mold in the vicinity of the meniscus is lower than that of other varieties. This is presumed to be the cause of frequent occurrence of restrictive breakout prediction signals.

  Therefore, the powder film (part 50 mm below the meniscus) attached to the mold after casting was collected, and the cross section of the film was observed. As a result, it was found that when steel with a low Al content was cast, bubbles were generated in the cross section of the film, and the amount of generated bubbles increased as the Al content of the varieties to be cast decreased. In particular, when the Al content in the steel is 0.010% by mass or less, the porosity of the powder film due to air bubbles may exceed 10%. For this reason, in Si killed steel with a low Al content, bubbles are generated in the powder film being cast and heat insulation is increased. In particular, the amount of heat removed from the solidified shell to the mold wall is reduced in the vicinity of the meniscus. It is thought that it has led to frequent occurrence of sex breakout prediction signals.

When the type of gas contained in the bubbles in the powder film was specified, it was found that the hydrogen content was large and the bubble component contained hydrogen gas or water vapor gas. It is considered that when the concentration of OH ⁻ dissolved in the molten powder film becomes equal to or higher than the saturation solubility, bubbles are generated as water vapor in the powder film.

As described in Non-Patent Document 1, at the interface between the molten slag and the gas phase, between the hydroxide ions in the slag and the water vapor in the gas phase,
2 (OH ⁻ ) ← → H ₂ O + (O ²⁻ ) [1]
There is a relationship. Here, (OH ⁻ ) and (O ²⁻ ) represent a hydroxide ion and an oxygen ion in the molten slag, respectively.

When the slag is in a high-temperature molten state, water vapor in the atmosphere dissolves in the slag, and the reaction from the right side to the left side of the formula [1] proceeds to form hydroxide ions in the slag. When the slag temperature decreases, a reaction occurs from the left side to the right side of the formula [1], and water vapor is generated as a gas phase. Non-Patent Document 1 is knowledge of CaO—SiO ₂ binary slag, but it is considered that the same principle is applicable to powders containing Na ₂ O, Al ₂ O ₃ , F, and the like.

  Therefore, the mold surface was shut off from the atmosphere during continuous casting, and the gas partial pressure in contact with the molten powder in the mold was replaced to reduce the water vapor partial pressure. The frequency of out prediction signals has decreased.

This invention is made | formed based on the said knowledge, The place made into the summary is as follows.
(1) A continuous casting method for steel with an Al content of less than 0.015% by mass, wherein the partial pressure of water vapor in the atmosphere in contact with the powder-coated surface in the continuous casting mold is reduced from the partial pressure of water vapor in the atmosphere. The continuous casting method of steel, wherein the water vapor partial pressure is 0.02 atm or less.
(2) In the above (1), a shielding plate is provided between the powder-coated surface in the continuous casting mold and the atmosphere, and a gas having a water vapor partial pressure of 0.02 atm or less is introduced into the shielding plate. The continuous casting method of the described steel.
(3) The continuous casting method for steel as described in (2) above, wherein the introduced gas is dry air.
(4) The continuous casting method for steel according to any one of (1) to (3) above, wherein the continuous casting of steel is slab continuous casting.

  The present invention reduces the partial pressure of water vapor in the atmosphere in contact with the powder-coated surface in the continuous casting mold from the partial pressure of water vapor in the atmosphere when continuously casting Si killed steel having an Al content of less than 0.015% by mass. By setting the water vapor partial pressure to 0.02 atm or less, the generation of bubbles in the powder film flowing between the mold and the solidified shell can be reduced, and the generation of a predictive signal for restrictive breakout can be reduced.

  The present invention is intended for steel having an Al content of 0.015 mass% or less. In order to deoxidize the dissolved oxygen remaining in the molten steel by decarburization refining, Si is contained in an amount of 0.05 mass% or more. Therefore, the target steel is referred to as Si killed steel here. The carbon concentration of the steel is not particularly specified, but low carbon steel of about 0.01 to 0.08 mass% is the main target, and medium carbon steel of about 0.09 to 0.40 mass% is also cast. Moreover, although it does not specifically limit about the slab to cast, Slab continuous casting becomes a main object. In the present specification, the Al content in steel means total Al.

  In continuous casting, a thermocouple is embedded in the mold wall to generate a breakout prediction signal in order to prevent the occurrence of a constraining breakout. As the fractured part of the solidified shell, which causes a constraining breakout, moves below the mold, the temperature rises unsteadily when the fractured part passes through this thermocouple installation, so it is predicted that a breakout will occur can do. If the casting speed is rapidly reduced when the prediction signal is generated, the breakage portion of the solidified shell can be repaired to prevent the occurrence of breakout.

  The occurrence frequency of the breakout prediction signal was compared for each Al content level of steel. In any case, the Si content of the steel is 0.05% by mass or more, and the Al content of 0.015% by mass or more can be called Al-Si killed steel, and the Al content is less than 0.015% by mass. Can be called Si killed steel. FIG. 1 is a diagram in which the horizontal axis represents the Al content and the vertical axis represents the breakout prediction signal generation frequency. As is clear from FIG. 1, as the Al content in the steel decreases, the occurrence frequency of the breakout prediction signal increases, which is particularly remarkable when the Al content is less than 0.015% by mass.

  In a product that frequently generates a breakout prediction signal, a breakout may occur because the countermeasure for preventing the occurrence of the breakout is not in time. Breakout does not occur at all in Al-Si killed steel with an Al content of 0.015 mass% or more, whereas the breakout occurrence rate is about 1.7% for varieties with an Al content of 0.010 mass% or less. It was.

  Therefore, the state of heat transfer between the solidified shell and the mold wall in the mold was investigated for each Al content of steel. The survey was conducted from two viewpoints. First, the cooling water temperature rise allowance of the entire mold long side surface was measured, and the amount of heat removed from the entire mold long side surface was compared. Second, the temperature of thermocouples embedded in a plurality of locations in the casting direction in the mold was measured, and the temperature distribution in the casting direction was compared. Casting varieties had an Al content of 0.008 mass% (low Al varieties), 0.017 mass% (medium Al varieties), and 0.036 mass% (high Al varieties), and the Si content was low. It is 0.05 mass% or more for Al varieties, and 0.006 to 0.01 mass% for medium Al varieties and high Al varieties. The basicity of the used powder for continuous casting was about 1.1 to 1.2.

The surface average heat flux of the entire long side surface was determined based on the cooling water temperature rise margin on the long side surface of the mold. The casting speed was about 1.5 m / min. As a result, the surface average heat flux was about 1500 kW / m ² · sec for medium Al and high Al varieties, while the surface average heat flux was about 1100 kW / m ² · sec for low Al varieties. .

  In the mold wall, thermocouples are embedded at four locations at a pitch of 120 mm in the casting direction. The uppermost thermocouple is 65 mm from the meniscus. The distance from the mold wall surface to the thermocouple tip is about 5 mm. When the thermocouple temperature was measured for the low Al and medium Al varieties, the results shown in FIG. 2 were obtained. The thermocouple temperature in the 2nd to 4th stages in the casting direction does not change much depending on the type, but the temperature of the thermocouple installed near the meniscus is about 160 ° C for the medium Al type, and about 110 ° C for the low Al type. A significantly lower temperature was observed. From this, it is clear that in the low Al varieties, the heat removal from the solidified shell to the mold wall is reduced particularly in the vicinity of the meniscus.

  From the above results, in spite of casting using the same continuous casting powder, in the low Al varieties, the extraction from the solidified shell near the meniscus to the mold wall is different from the medium Al varieties and high Al varieties. It was found that the amount of heat was greatly reduced. Since there was no tendency for the thickness of the powder film existing between the solidified shell and the mold wall to vary by type, the difference in the amount of heat removal is not the difference in the thickness of the powder film. In addition, regarding the crystallization rate of the powder film, since there was no tendency for the crystallization rate to change for each type, the difference in the amount of heat removal is not the difference in the crystallization rate.

  Therefore, a powder film remaining on the wall of the mold after casting was collected and investigated. A powder film was sampled from a position about 50 mm from the meniscus, which has a large effect on the heat removal behavior near the meniscus.

  FIG. 3 shows a cross-sectional photograph of a powder film collected after casting a low Al variety. The black circles seen in the photos are voids. The voids in the film cross section were most severe in the film after casting the low Al type, less in the medium Al type, and hardly observed in the film after casting the high Al type. FIG. 4 shows the relationship between the Al content in the steel and the porosity, which was calculated based on the cross-sectional photograph. As is clear from FIG. 4, the low Al varieties have a remarkably high porosity. It is clear that the lower the Al content in the steel, the more air bubbles are present in the powder film existing between the solidified shell and the mold wall.

  From the above results, it was estimated that the cause of the decrease in the amount of heat removal in the vicinity of the meniscus in the continuous casting of low Al varieties was caused by the frequent occurrence of bubbles in the powder film and the increased porosity. .

  The gas analysis of the gas contained in the bubbles in the powder film was obtained from the spectrum integrated intensity ratio by mass number. As a result, the most abundant gas was nitrogen or carbon monoxide, but each sample was characterized by containing hydrogen gas at a ratio of 7 to 16%. Since hydrogen gas was detected, it is presumed that the interaction between the molten slag and water vapor is related to the generation of bubbles in the powder film.

Next, OH in Powder ^- it describes a method for quantifying hydrogen present as. Until now, the analysis of OH ⁻ in slag has been performed by the molten Al reduction method. In this method, OH ⁻ in the slag is reduced to H ₂ gas with Al, and OH ⁻ is quantified by measuring the amount of H ₂ gas with a gas mass spectrometer. However, with continuous casting powder containing F or Na ₂ O, this method cannot be used because NaF and SiF ₄ gases are generated during heating. Therefore, OH ^- was analyzed using nuclear magnetic resonance (solid NMR). The NMR spectrum of H was measured for the powder before casting and the powder film collected after casting. Kaolinite Al ₂ Si ₂ O ₅ (OH) ₄ was used as a standard sample. Since it is known to contain 1.56% by weight of H as, powder samples OH ^{- -} kaolinite OH know the ratio of the area value of the NMR spectrum corresponding to the ^- OH of the area value and the standard samples of the NMR spectrum corresponding to Thus, the weight of H present as OH ⁻ in the powder was quantified.

The H present as OH ⁻ of the powder before casting was 80 ppm. On the other hand, the powder film after casting the low Al type increased to 120-150 ppm. On the other hand, the powder film after casting the medium / high Al type was as low as 40-80 ppm. From this result, in the medium and high Al varieties, Al in the molten steel reacts with powder melting pool OH ^- Since lowering the ion concentration relative to the air bubbles are not generated, Al in the molten steel at low Al varieties Therefore, the degree of lowering the OH ion concentration of the molten powder pool is low, and OH ^- ions remain in the powder film at a high concentration. As a result, in the low Al variety, the OH ⁻ ion concentration in the powder film exceeds the dissolution concentration during the cooling process, and water vapor bubbles are generated in the powder film.

As described in Non-Patent Document 1, at the interface between the molten slag and the gas phase, between the hydroxide ions in the slag and the water vapor in the gas phase,
2 (OH ⁻ ) ← → H ₂ O + (O ²⁻ ) [1]
There is a relationship. Here, (OH ⁻ ) and (O ²⁻ ) represent a hydroxide ion and an oxygen ion in the molten slag, respectively.

When the steel used for continuous casting is Al killed steel containing Al or Al—Si killed steel, 3 (OH ⁻ ) +2 [Al] → (Al ₂ O ₃ ) +3 [between the molten powder and the molten steel. H] + 3e ^- [2]
Reaction occurs. As a result, the hydroxide ions in the molten powder are reduced by Al in the molten steel and move as hydrogen into the molten steel. Therefore, even if water vapor in the atmosphere is taken into the molten powder as hydroxide ions, it is reduced by Al, so the hydroxide ion concentration in the molten powder does not rise sufficiently and the temperature of the molten powder decreases. Water vapor bubbles are not generated.

  In the case where the steel used for continuous casting is Si killed steel with a low Al content, there is no reduction of hydroxide ions due to the reaction of the above formula [2]. The reason why many bubbles are generated in the continuous cast powder film in the Si killed steel with a low Al content can be explained as described above.

  From the above analysis, it is possible that the generation of bubbles can be prevented if an increase in the OH ion concentration in the molten powder can be suppressed even in a low Al variety.

When the powder is in a high-temperature molten state, water vapor in the atmosphere dissolves in the molten powder, and the reaction from the right side to the left side of the formula [1] proceeds to form hydroxide ions in the molten powder. When the molten powder temperature decreases, a reaction occurs from the right side to the left side of the formula [1], and water vapor is generated as a gas phase. Non-Patent Document 1 is knowledge of CaO—SiO ₂ binary slag, but it is considered that the same principle is applicable to powders containing Na ₂ O, Al ₂ O ₃ , F, and the like.

That is, by lowering the partial pressure of water vapor in the gas phase in contact with the molten powder to suppress the progress of the reaction to the left side from the right side of the above formula [1], in the molten powder - should be able to reduce the concentration ^(OH) .

The water vapor partial pressure in the atmosphere rises to about 0.04 atm in summer when the temperature is high, and falls to about 0.005 atm in winter when the temperature is low. Therefore, a powder film obtained by casting Si killed steel was sampled in each season of the year, and the (OH ⁻ ) concentration in the powder film was compared. As a result, as shown in FIG. 5, it was found that the (OH ⁻ ) concentration in the powder film decreased in the winter compared to the summer.

  Therefore, a shielding plate as shown in FIG. 6 is provided between the powder-coated surface in the continuous casting mold and the atmosphere, and dry air having a partial pressure of water vapor of 0.010 atm is introduced into the shielding plate. An attempt was made to reduce the partial pressure of water vapor in the portion in contact with the molten powder. Even when the season was summer and the partial pressure of water vapor in the atmosphere was as high as 0.04 atm, the partial pressure of water vapor in the mold and in contact with the molten powder could be reduced to 0.015 atm.

Next, when this shield plate and gas introduction were used to cast Si killed steel throughout the year, it was found that the (OH ⁻ ) concentration in the powder film was kept low throughout the year including summer.

Based on the above results, variously changing the partial pressure of water vapor in the atmosphere in contact with the powder-coated surface in the continuous casting mold, performing slab continuous casting of Si-killed steel having an Al content of less than 0.015% by mass, The relationship between the (OH ⁻ ) concentration in the powder film, the porosity in the powder film taken from the mold cross section, the breakout prediction signal generation rate, and the water vapor partial pressure was investigated. The basicity of the used continuous casting powder is about 1.0 to 1.2. As shown in FIG. 7, FIG. 8, and FIG. 9, the lower the water vapor partial pressure in the portion in contact with the powder coating surface in the continuous casting mold, the lower the (OH ⁻ ) concentration in the powder film, the powder collected from the mold cross section. Generates a breakout prediction signal if the void ratio in the film and the breakout prediction signal generation rate are both reduced, and the partial pressure of water vapor in the atmosphere in contact with the powder coating surface in the continuous casting mold is 0.02 atm or less. It became clear that the frequency could be reduced sufficiently.

  A continuous casting method of steel having an Al content of less than 0.015% by mass, wherein the partial pressure of water vapor in the atmosphere in contact with the powder-coated surface in the continuous casting mold is reduced from the partial pressure of water vapor in the atmosphere, In order to make the pressure 0.02 atm or less, it is preferable to provide a shielding plate between the powder-coated surface in the continuous casting mold and the atmosphere, and introduce a gas having a water vapor partial pressure of 0.02 atm or less into the shielding plate. The shielding plate may be any material that can withstand the ambient temperature around the mold, and may be a stainless steel plate or the like. Desirably, a transparent material is preferable so that the condition of the molten metal surface in the mold can be observed, but a window may be provided partially. In addition, in the case of a mold equipped with a powder feeder, the shielding plate needs to be in a position and structure that does not interfere with the powder feeder.

  Moreover, it is preferable to use dry air as the gas introduced into the shielding plate. This is because it can be supplied at low cost.

  The continuous casting of steel to which the present invention is applied is preferably slab continuous casting. In continuous casting of Si killed steel having an Al content of less than 0.015% by mass, generation of a breakout prediction signal due to bubbles generated in the powder film is unique to slab continuous casting, and the effect of the present invention is particularly It is because it is demonstrated.

  In addition, the improvement effect becomes more remarkable in the steel having an Al content of 0.010% by mass or less. In addition, the effect is remarkable in slab continuous casting. Although the effects of the present invention can be obtained regardless of the carbon concentration in the steel, the occurrence of vertical cracks in conventional slabs is always a problem, especially for low carbon steel having a C content of 0.08% by mass or less. It can be said that the special effect is exhibited especially from the relationship in which the low basicity powder was used. The present invention is preferably applied only to Si killed steel having a low Al content, or to only some varieties including Si killed steel.

  In continuous casting with a slab continuous casting machine of vertical bending type, the partial pressure of water vapor in the atmosphere in contact with the molten powder in the mold was changed, and the frequency of occurrence of breakout prediction signals was compared for each Al content level of steel. . In any case, the Si content of the steel is 0.05% by mass or more. The continuous casting powder components used are as shown in Table 1.

  The circles in FIG. 10 are the results of casting in the summer with the atmosphere in contact with the powder-coated surface in the continuous casting mold being an atmospheric atmosphere. The water vapor partial pressure in the atmosphere in contact with the molten powder was about 0.04 atm. Further, a shielding plate 2 as shown in FIG. The shielding plate 2 is made of stainless steel, and shields the upper surface, both side surfaces, and the rear surface of the mold 1 from the atmosphere. The front side is open because it is necessary to feed powder from the powder feeder 5 to the hot water surface 6. About the upper surface of the shielding board 2, the notch part is provided in the position which inserts the immersion nozzle 3. As shown in FIG. By introducing dry air having a water vapor partial pressure of 0.010 atm into the shielding plate 2 through the dry air supply pipe 4, the water vapor partial pressure of the portion in contact with the molten powder in the mold may be 0.02 atm or less. did it. The case where the shielding plate 2 is provided and cast is indicated by ◎ in FIG. As is apparent from FIG. 10, in the Si killed steel having an Al content of less than 0.015% by mass, the breakout prediction signal is frequently generated at a water vapor partial pressure of 0.04 atm, whereas the water vapor partial pressure is high. In the case of 0.02 atm or less, it can be seen that the frequency of breakout prediction signal generation is drastically reduced. In particular, the effect is remarkable in varieties having an Al content of 0.010% by mass or less.

  The breakout frequency was about 1.7% when steel with an Al content of 0.010% by mass or less was cast in an air atmosphere, whereas the breakout frequency was in contact with the molten powder. When the water vapor partial pressure was 0.02 atm or less, no breakout occurred at any Al content level.

It is a figure which shows the relationship between Al content in steel, and a breakout prediction signal generation rate. It is a figure which shows the relationship between Al content in steel, and the thermocouple temperature in a casting mold according to casting direction. It is a figure which shows the cross-sectional photograph of the powder film after low Al kind casting. It is a figure which shows the relationship between Al content in steel, and the porosity in a powder film. It is a figure which shows the relationship between the casting time throughout the year, and the (OH < ^- >) ion concentration in a powder film. It is a figure which shows the shielding board for reducing the water vapor partial pressure of the powder coating surface in a continuous casting mold, (a) is a perspective view, (b) is a cross-sectional view. It is a figure which shows the relationship between water vapor partial pressure and the (OH < ^- >) density | concentration in a powder film. It is a figure which shows the relationship between water vapor partial pressure and the porosity in a powder film. It is a figure which shows the relationship between water vapor partial pressure and a breakout prediction signal generation rate. It is a figure which shows the relationship between Al content in steel, and a breakout prediction signal generation rate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Mold 2 Shielding board 3 Immersion nozzle 4 Dry air supply pipe 5 Powder feeder 6 Hot water surface (powder surface)

Claims (4)

  A continuous casting method of steel having an Al content of less than 0.015% by mass, wherein the partial pressure of water vapor in the atmosphere in contact with the powder-coated surface in the continuous casting mold is reduced from the partial pressure of water vapor in the atmosphere, A continuous casting method of steel, characterized in that the pressure is 0.02 atm or less.   The steel according to claim 1, wherein a shielding plate is provided between the powder-coated surface in the continuous casting mold and the atmosphere, and a gas having a water vapor partial pressure of 0.02 atm or less is introduced into the shielding plate. Continuous casting method.   The continuous casting method for steel according to claim 2, wherein the gas to be introduced is dry air.   4. The steel continuous casting method according to claim 1, wherein the continuous casting of steel is slab continuous casting.