TWI654042B - Steel melting method - Google Patents

Abstract

The method for melting the steel is a method of melting steel composed of Al deoxidized steel containing Mn and Ti, and has the following steps: one refining step, one refining in the converter; and, a secondary refining step, the molten steel is The converter is transferred to a processing furnace, and the composition of the molten steel is adjusted in the processing furnace, and the secondary refining step has the following steps: an Al raw material supply step, and an Al raw material is supplied to the molten steel in the processing furnace; a raw material supply step of supplying a Mn raw material to the molten steel in the treatment furnace at the same time as the Al raw material supply step or after the Al raw material supply step; and a Ti raw material supply step, after the Al raw material supply step, and At the same time as the Mn raw material supply step or after the Mn raw material supply step, the Ti raw material is supplied to the molten steel in the treatment furnace.

Description

Steel melting method

The present invention relates to a method for producing a steel of a steel cast piece obtained from Al deoxidized steel containing Mn and Ti. The case is based on Japanese Patent Application No. 2017-029645, which was filed on February 21, 2017 in Japan, and its contents are hereby incorporated by reference.

BACKGROUND OF THE INVENTION Generally, in the continuous casting of steel slabs, after the refining of the converter, the molten steel is transferred to a processing furnace equipped with a vacuum chamber, and secondary refining is performed in the processing furnace to perform composition adjustment, and then The resulting molten steel is supplied to a continuous casting apparatus. In the continuous casting apparatus, the molten steel accumulated in the tundish is supplied into the mold through a nozzle or the like to continuously cast the cast piece of the set shape.

Here, when the molten steel conveying path such as the nozzle is blocked in the casting, it is difficult to continue the casting, and the predetermined casting amount cannot be cast. That is, it may become impossible to perform the predetermined number of consecutive continuous castings, and there is a case where the molten steel of the tub is returned. Further, inclusions or the like adhering to the nozzle or the like are caught in the cast piece at the time of casting, and there is a problem that the quality of the cast piece is lowered.

In particular, in Al deoxidized steel in which aluminum is added for deoxidation, alumina is present as an inclusion in the molten steel, and alumina or a metal block adheres to a refractory material such as a nozzle and grows, so that molten steel is easily generated. The tendency of the path to block. Therefore, in the prior art, a technique in which an Ar gas is blown into a molten steel conveyance path such as a nozzle to suppress adhesion of alumina or a metal block is performed (for example, refer to Patent Documents 1 to 4).

CITATION LIST Patent Literature Patent Literature 1: Japanese Patent Laid-Open Publication No. JP-A No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. JP-A-2010-167495

SUMMARY OF THE INVENTION Problem to be Solved by the Invention Here, the state in which the molten steel conveying path is clogged is greatly different depending on the composition of the molten steel. In the Al deoxidized steel containing, for example, Mn and Ti, even if the heating nozzle or the Ar gas is blown as described above, the clogging of the molten steel conveying path cannot be sufficiently suppressed, and the predetermined number of consecutive continuous castings cannot be performed.

The present invention has been made in view of the above circumstances, and an object of the invention is to provide a method for melting a steel which can stably perform casting even when continuously casting an Al deoxidized steel containing Mn and Ti while suppressing clogging of a molten steel conveying path. .

Means for Solving the Problems In order to solve the above problems, the present invention employs the following method. (1) An aspect of the present invention is a method of melting steel composed of Al deoxidized steel containing Mn and Ti, comprising the steps of: one refining step, one refining in a converter; and, a second refining step, The molten steel is transferred from the converter to the processing furnace, and the molten material is supplied with the Al raw material, the Mn raw material and the Ti raw material in the processing furnace to adjust the composition of the composition, wherein the secondary refining step performs the following steps: Supplying the aforementioned Al raw material in the molten steel in the furnace, and then supplying the Mn raw material and supplying the Ti raw material sequentially or simultaneously; or sequentially or simultaneously supplying the Al raw material and supplying the Mn to the molten steel in the processing furnace The raw material is then supplied to the aforementioned Ti raw material.

(2) In the method for melting steel according to (1) above, the Al raw material may be supplied in the secondary refining step, and then the Mn raw material may be supplied sequentially or simultaneously and the Ti raw material may be supplied. (3) In the method for melting steel according to the above (2), the supply of the Mn raw material may be started after 30 seconds or more has elapsed after the supply of the Al raw material is completely completed. (4) In the method for melting steel according to (2) or (3) above, in the secondary refining step, the Al raw material may be supplied, and then the Mn raw material may be sequentially supplied and the Ti raw material may be supplied. (5) In the method for melting steel according to the above (4), the supply of the Ti raw material may be started after 30 seconds or more has elapsed after the supply of the Mn raw material is completely completed. (6) In the method for melting a steel according to any one of the above (2) to (5), when the Al raw material is supplied to the molten steel, the oxygen in the molten steel may be 150 ppm by mass ratio. the above.

(7) In the method for melting steel according to (1) above, in the secondary refining step, the Al raw material may be supplied sequentially or simultaneously, and the Mn raw material may be supplied, and then the Ti raw material may be supplied. (8) In the method for melting steel according to the above (7), the supply of the Ti raw material may be started after 30 seconds or more has elapsed after the supply of the Mn raw material is completely completed.

(9) In the method for melting steel according to any one of the above (1) to (8), the oxygen may be blown in the secondary refining step. (10) In the method for melting steel according to the above (9), the oxygen may not be blown in the following period: one minute before the supply of the Al raw material is started, and one minute after the supply of the Al raw material is completed. Period: a period from 1 minute before the supply of the Mn raw material to the end of the supply of the Mn raw material, and a period from 1 minute before the supply of the Ti raw material to the end of the supply of the Ti raw material. (11) In the method for melting steel according to any one of the above (1) to (10), when the secondary refining step is completely completed, the molten steel may contain C: 0.0013% or more and 0.040 by mass ratio. % or less, Al: 0.01% or more and 0.10% or less, Mn: 0.20% or more and 3.00% or less, and Ti: 0.004% or more and 0.100% or less.

According to the method for melting steel according to the above (1), it is possible to prevent the Mn raw material from coexisting with the Al raw material in the molten steel in the treatment furnace, and/or to prevent the Mn raw material and the Ti raw material from coexisting in the molten steel in the treatment furnace, so that It is possible to suppress the formation of a composite oxide (MnO, Al ₂ O ₃ ) of Mn and Al and/or a composite oxide (MnO, TiO _X ) of Mn and Ti. That is, in the molten steel in the treatment furnace, for example, MnO, Al ₂ O ₃ and TiO _X may exist alone, and even if MnO is reduced by Al contained in the molten steel or Ti added later, high melting point is not formed. A composite oxide of Al and Ti (Al ₂ O ₃ · TiO _X ) suppresses clogging of the molten steel transportation path. Thereby, the predetermined number of consecutive continuous castings can be stably performed.

According to the method for melting steel according to the above (2), it is possible to prevent the Mn raw material and the Al raw material from coexisting in the molten steel in the treatment furnace, and to suppress the formation of the composite oxide (MnO, Al ₂ O ₃ ) of Mn and Al.

According to the method for melting steel according to the above (3), the Mn raw material can be supplied in a state in which the supplied Al raw material has been melted in the molten steel and uniformly dispersed. Thereby, it is possible to more reliably prevent the Mn raw material and the Al raw material from coexisting on the molten steel in the treatment furnace, and it is possible to further suppress the formation of the composite oxide (MnO, Al ₂ O ₃ ) of Mn and Al. According to the melting method of the steel of the above (4), not only the Mn raw material and the Al raw material can be prevented from coexisting in the molten steel in the processing furnace, but also the Mn raw material and the Ti raw material can be prevented from coexisting in the molten steel in the processing furnace, so A composite oxide (MnO, Al ₂ O ₃ ) of Mn and Al and a composite oxide (MnO, TiO _X ) of Mn and Ti are formed. Therefore, the blockage of the molten steel conveying path can be further suppressed. According to the method for melting steel according to the above (5), the Ti raw material can be supplied in a state in which the supplied Mn raw material has been melted in the molten steel and uniformly dispersed. Thereby, it is possible to more reliably prevent the Mn raw material and the Ti raw material from coexisting in the molten steel in the treatment furnace, and it is possible to further suppress the formation of the composite oxide (MnO, TiO _x ) of Mn and Ti. Further, even in the method of (6), the oxygen in the molten steel is in a relatively high state of 150 ppm or more in mass ratio, and since the Mn raw material is supplied after the Al raw material is supplied and the Al raw material has been melted according to the above-described melting method, By supplying an Al raw material, the oxygen content in the molten steel can be sufficiently reduced, and formation of a composite oxide (MnO, Al ₂ O ₃ ) of Mn and Al can be suppressed. Therefore, even when the Al deoxidized steel containing Mn and Ti is continuously cast, the clogging of the molten steel conveying path can be suppressed, and the casting can be stably performed.

According to the method for melting steel according to the above (7), it is possible to prevent the Mn raw material and the Ti raw material from coexisting in the molten steel in the treatment furnace, and to suppress the formation of the composite oxide (MnO, TiO _x ) of Mn and Ti. According to the method for melting steel according to the above (8), the Ti raw material can be supplied in a state in which the supplied Mn raw material has been melted in the molten steel and uniformly dispersed. Thereby, it is possible to more reliably prevent the Mn raw material and the Ti raw material from coexisting in the molten steel in the treatment furnace, and it is possible to further suppress the formation of the composite oxide (MnO, TiO _x ) of Mn and Ti.

According to the method for melting steel according to the above (9), the temperature of the molten steel in the treatment furnace can be raised by blowing oxygen. According to the method for melting steel according to the above (10), since oxygen, which is not supplied with Ti, Al, and Mn, which has a high oxygen concentration immediately after oxygen gas is blown, is not blown, it is possible to prevent Al oxide and Mn. Excessive formation of oxides and Ti oxides. In addition, since there has always been a concern that if the oxygen is blown into the treatment furnace, the inclusions will increase, so the shutdown temperature of the converter will be set higher, and the implementation of blowing oxygen into the treatment furnace is limited. The temperature of the molten steel can be raised in the treatment furnace by appropriately arranging the time point at which oxygen is blown as described above. Therefore, it is not necessary to set the shutdown blow temperature of the converter above the required level, and it is also possible to reduce the energy cost. According to the method for melting steel according to the above (11), when the secondary refining step is completely completed, a molten steel having a chemical composition of the following chemical composition can be obtained, and the chemical composition is C: 0.0013% or more and 0.040% or less, Al. : 0.01% or more and 0.10% or less, Mn: 0.20% or more and 3.00% or less, and Ti: 0.004% or more and 0.100% or less.

Advantageous Effects of Invention As described above, according to the present invention, it is possible to provide a method for melting a steel which can stably perform casting even when continuously casting an Al-deoxidized steel containing Mn and Ti while suppressing clogging of a molten steel conveying path.

EMBODIMENT OF THE INVENTION The inventors of the present invention have made intensive studies to solve the above problems, and have confirmed that the composite oxide of Al and Ti (Al ₂ O ₃ · TiO _X ) is one of the causes of the clogging of the molten steel transportation path. Therefore, the following knowledge is obtained: the composite oxide of Al and Ti (Al ₂ O ₃ · TiO _X ) is a composite oxide of Mn and Al (MnO) added to the Ti in the molten steel in the secondary refining step. A product produced by preferentially reducing MnO of Al ₂ O ₃ ) or a product obtained by preferentially reducing MnO of a composite oxide of Mn and Ti (MnO·TiO _X ) due to Al in the molten steel. And the following knowledge is known: the composite oxide of Mn and Al (MnO·Al ₂ O ₃ ), and the composite oxide of Mn and Ti (MnO·TiO _X ) have a low melting point, and are solid-liquid two phases in the molten steel. Coexisting state or inclusions in a liquid phase state, but when the MnO of the composite oxide is reduced by Al or Ti to form a composite oxide of Al and Ti (Al ₂ O ₃ · TiO _X ), the melting point becomes high. , and become the main reason for the blockage of the molten steel conveying path.

The present invention has been made in view of the above knowledge. Hereinafter, the method of melting the steel according to the present invention will be described with reference to the accompanying drawings in accordance with the embodiments. Further, the present invention is not limited to the following embodiments.

(First Embodiment) Hereinafter, a method of melting a steel according to a first embodiment of the present invention will be described. The method for melting steel according to the present embodiment is a method of melting steel composed of Al deoxidized steel containing Mn and Ti, and has a primary refining step and a secondary refining step.

In the steel melting method of the present embodiment, the steel slab to be used is composed of Al deoxidized steel containing Mn and Ti, and specifically, the C content is set to 0.0013% or more by mass ratio. 0.040% or less, the Al content is 0.01% or more and 0.10% or less, the Mn content is 0.20% or more and 3.00% or less, and the Ti content is 0.004% or more and 0.100% or less. Therefore, when the secondary refining step is completely completed, the molten steel component is adjusted so as to contain C: 0.0013% or more and 0.040% or less, Al: 0.01% or more and 0.10% or less, and Mn: 0.20% or more and 3.00% by mass ratio. Hereinafter, Ti: 0.004% or more and 0.100% or less. More preferably, when the secondary refining step is completely completed, the molten steel component is adjusted to contain C: 0.0032% or more and 0.040% or less, Al: 0.01% or more and 0.10% or less, and Mn: 0.20% by mass ratio. The above is 3.00% or less, and Ti: 0.004% or more and 0.100% or less.

First, in one refining step, one refining of the molten steel is performed in the converter.

Next, in the secondary refining step, the molten steel is transferred from the converter to the treatment furnace, and secondary refining for adjusting the composition of the molten steel is performed in the treatment furnace. Further, in the secondary refining step, when decarburization is necessary, the decarburization treatment is first performed to adjust the amount of carbon, and then, while Al is supplied for deoxidation, the constituent elements are supplied to the molten steel to adjust the composition.

As the treatment furnace, a treatment furnace 10 having a vacuum chamber 11 as shown in Fig. 1 can be used. As shown in Fig. 1, the processing furnace 10 includes a vacuum chamber 11, an exhaust unit 12 that discharges the gas in the vacuum chamber 11 to the outside, a suction pipe 13 that sucks the molten steel into the vacuum chamber 11, and a vacuum chamber 11 The discharge pipe 15 through which the molten steel is discharged and the element supply portion 17 that supplies the raw material (additive material) to the molten steel in the vacuum chamber 11 are provided. Further, an inert gas introduction mechanism 14 for introducing an inert gas (Ar gas in the present embodiment) is disposed on the suction pipe 13.

In the steel melting method of the present embodiment, the Al raw material is supplied to the molten steel in the processing furnace in the secondary refining step, and then the Mn raw material and the Ti raw material are supplied. That is, the Al raw material is supplied to the molten steel in the vacuum chamber 11, and then the supplied Al raw material is melted in the molten steel and uniformly dispersed, and then the Mn raw material and the Ti raw material are supplied. Further, in the steel melting method of the present embodiment, the Mn raw material and the Ti raw material may be sequentially supplied, or may be simultaneously performed.

According to the steel melting method of the present embodiment, since the Mn raw material is supplied after the Al raw material is supplied and the Al raw material is melted, it is possible to prevent the Mn raw material and the Al raw material from coexisting in the molten steel in the processing furnace. Therefore, formation of a composite oxide (MnO, Al ₂ O ₃ ) of Mn and Al can be suppressed. That is, in the molten steel in the treatment furnace, for example, MnO and Al ₂ O ₃ may exist alone, and even if MnO is reduced by the added Ti, a high melting point composite oxide of Al and Ti (Al ₂ O is not formed). ₃ ·TiO _X ), which can suppress the blockage of the molten steel conveying path. Thereby, the predetermined number of consecutive continuous castings can be stably performed.

Here, when the Al raw material is supplied to the molten steel, the oxygen in the molten steel may be 150 ppm or more in mass ratio. In general, when a molten steel having an oxygen content of 150 ppm or more in mass ratio is used for secondary refining using an Al raw material and a Mn raw material, a composite oxide of Mn and Al (MnO·Al ₂ O ₃ ) is easily formed. However, according to the method for melting steel according to the present embodiment, the Mn raw material is supplied after the Al raw material is supplied and the Al raw material is melted, so that the oxygen content in the molten steel can be sufficiently reduced by supplying the Al raw material. Therefore, even when the Al content is supplied to the molten steel, the oxygen content of the molten steel is 150 ppm or more by mass ratio, and formation of a composite oxide (MnO, Al ₂ O ₃ ) of Mn and Al can be suppressed. Therefore, even when the Al deoxidized steel containing Mn and Ti is continuously cast, the clogging of the molten steel conveying path can be suppressed, and the casting can be stably performed.

In addition, for the molten steel having a higher oxygen in the molten steel, if the Mn raw material is first supplied, MnO is formed in the vacuum chamber 11, and when the Al raw material is put therein, the composite oxide of Mn and Al is formed. (MnO・Al ₂ O ₃ ) doubts.

Further, it is preferable to supply the Mn raw material after the Al raw material is supplied to the molten steel in the vacuum chamber 11 for 30 seconds or more. This is because the Al raw material can be surely melted by allowing the Al raw material to be supplied for 30 seconds or more. Further, it is more preferable to supply the Mn raw material after the Al raw material is supplied to the molten steel in the vacuum chamber 11 for one minute or more.

When the Mn raw material and the Al raw material coexist on the molten steel, a composite oxide of Mn and Al (MnO·Al ₂ O ₃ ) is formed by the oxygen contained in the Mn raw material. Since the composite oxide (MnO, Al ₂ O ₃ ) of Mn and Al has a low melting point, it is present in the molten steel as an inclusion of a solid-liquid two-phase coexisting state. Then, when the MnO of the composite oxide of Mn and Al (MnO, Al ₂ O ₃ ) is reduced by the added Ti, a composite oxide of Al and Ti (Al ₂ O ₃ · TiO _X ) is formed. Since the composite oxide of Al and Ti (Al ₂ O ₃ · TiO _X ) has a high melting point, it adheres to the inner wall of the molten steel conveying path such as a nozzle, and causes the molten steel conveying path to be blocked.

Therefore, in the steel melting method of the present embodiment, the supply time point of the Al raw material and the supply time point of the Mn raw material are adjusted so that the Mn raw material and the Al raw material do not coexist in the molten steel in the vacuum chamber 11.

Further, in this secondary refining step, oxygen gas blowing may be performed in order to increase the temperature of the molten steel in the vacuum chamber 11. When oxygen is blown, in order to suppress the oxidation of Ti, Al, and Mn supplied, and to suppress the formation of excessive Ti oxide, Al oxide, and Mn oxide, it is preferable to supply the Al raw material, the Mn raw material, and the Ti raw material. Staggered with oxygen for a period of more than 1 minute. In other words, as shown in Fig. 2, it is preferable not to perform oxygen blowing in the following period: from 1 minute before the start of the supply of the Al raw material to the end of the supply of the Al raw material for 1 minute, from the start of the supply of the Mn raw material 1 minute before the start The period from the completion of the supply of the Mn raw material for one minute, and the period from the start of the supply of the Ti raw material for one minute to the end of the supply of the Ti raw material for one minute.

The molten steel obtained by adjusting the composition as described above is supplied to a continuous casting apparatus, and the steel cast piece is continuously cast.

According to the steel melting method of the present embodiment configured as described above, the molten steel in the vacuum chamber 11 is supplied to the molten steel in the vacuum chamber 11 in the secondary refining step. After the supplied Al raw material has been melted in the molten steel and uniformly dispersed, the Mn raw material is supplied to the molten steel in the vacuum chamber 11, so that the Mn raw material and the Al raw material do not coexist on the steel, and Mn and Mn can be suppressed. Al composite oxide (MnO, Al ₂ O ₃ ) is formed. By this means, even if Ti is added, the formation of a composite oxide (Al ₂ O ₃ , TiO _X ) of Al and Ti having a high melting point can be suppressed, and the molten steel conveying path can be prevented from being clogged, and the predetermined operation can be stably performed. The number of consecutive continuous castings. Further, it is possible to suppress the inclusion of inclusions, and it is possible to manufacture a high-quality cast piece.

In addition, when the oxygen is blown in the secondary refining step, the Al oxide and the Mn can be suppressed by shifting the supply timing of the Al raw material, the Mn raw material, and the Ti raw material to the oxygen injection time point by one minute or more. The oxide and the Ti oxide are excessively formed, and the inclusion of the inclusions can be further suppressed. Further, since the temperature of the molten steel in the vacuum chamber 11 can be raised by blowing oxygen, it is not necessary to set the shutdown temperature of the converter above the required level, and the energy cost can be reduced.

Further, in the steel melting method of the present embodiment, it is preferable to sequentially supply the Mn raw material and the Ti raw material in the secondary refining step, that is, in the secondary refining step, it is preferable to use the Al raw material, the Mn raw material, and the Ti raw material. The order is supplied to the molten steel. At this time, since the Ti raw material is supplied after the Mn raw material is supplied and the Mn raw material is melted, it is possible to prevent the Mn raw material and the Ti raw material from coexisting in the molten steel in the processing furnace. Therefore, formation of a composite oxide (MnO, TiO _x ) of Mn and Ti can be suppressed. The composite oxide of Mn and Ti (MnO, TiO _X ) is reduced by Al in the molten steel, whereby a composite oxide of Al and Ti (Al ₂ O ₃ · TiO _X ) is formed, and thus Mn and Al are combined. Like the composite oxide (MnO, Al ₂ O ₃ ), it adheres to the inner wall of the molten steel conveying path such as a nozzle, and causes the molten steel conveying path to be blocked. Therefore, by avoiding the formation of the composite oxide (MnO, Al ₂ O ₃ ) of Mn and Al and avoiding the formation of the composite oxide (MnO, TiO _x ) of Mn and Ti, it is possible to more reliably prevent the molten steel transport path from being clogged.

Further, in the secondary refining step, even when the molten material is supplied in the order of the Al raw material, the Mn raw material, and the Ti raw material, in order to allow the Mn raw material to be surely melted, it is preferable to supply the Mn raw material to the molten steel in the vacuum chamber 11 after the molten steel is supplied. After 30 seconds or more, the Ti raw material is supplied, and it is more preferable to supply the Ti raw material after 1 minute or more.

(Second embodiment) Hereinafter, a method of melting a steel according to a second embodiment of the present invention will be described. In the method for melting steel according to the present embodiment, the order of supplying the Al raw material, the Mn raw material, and the Ti raw material to the molten steel in the processing furnace in the secondary refining step is different from that of the first embodiment, and the first embodiment will be omitted below. Explain the repeated instructions.

In the steel melting method of the present embodiment, the Al raw material is supplied to the molten steel in the processing furnace and the Mn raw material is supplied in the secondary refining step, and then the Ti raw material is supplied. That is, the Al raw material and the Mn raw material are supplied to the molten steel in the vacuum chamber 11, and then the supplied Mn raw material is melted in the molten steel and uniformly dispersed, and then the Ti raw material is supplied. Further, in the steel melting method of the present embodiment, the Al raw material and the Mn raw material may be sequentially supplied, or may be simultaneously performed.

According to the steel melting method of the present embodiment, since the Mn raw material is supplied and the Mn raw material is melted, the Ti raw material is supplied, so that the Mn raw material and the Ti raw material can be prevented from coexisting in the molten steel in the processing furnace. Therefore, formation of a composite oxide (MnO, TiO _x ) of Mn and Ti can be suppressed. That is, in the molten steel in the treatment furnace, for example, MnO and TiO _X may exist alone, and even if MnO is reduced by Al contained in the molten steel, a high melting point composite oxide of Al and Ti is not formed (Al). ₂ O ₃ · TiO _X ), which suppresses the blockage of the molten steel conveying path. Thereby, the predetermined number of consecutive continuous castings can be stably performed.

Further, it is preferable to supply the Ti raw material after the Mn raw material is supplied to the molten steel in the vacuum chamber 11 for 30 seconds or more. This is because the Mn raw material can be surely melted by allowing the Mn raw material to pass for 30 seconds or more. It is preferable that the Mn raw material is supplied to the molten steel in the vacuum chamber 11 and then the Ti raw material is supplied after one minute or more.

When the Mn raw material and the Ti raw material coexist on the molten steel, a composite oxide of Mn and Ti (MnO·TiO _X ) is formed. Since the composite oxide of Mn and Ti (MnO·TiO _X ) has a low melting point, it is present as a inclusion in a liquid phase state in the molten steel. Then, when MnO of the composite oxide of Mn and Ti (MnO, Al ₂ O ₃ ) is reduced by Al in the molten steel, a composite oxide of Al and Ti (Al ₂ O ₃ · TiO _X ) is formed. Since the composite oxide of Al and Ti (Al ₂ O ₃ · TiO _X ) has a high melting point, it adheres to the inner wall of the molten steel conveying path such as a nozzle, and causes the molten steel conveying path to be blocked.

Therefore, in the steel melting method of the present embodiment, the supply time point of the Mn raw material and the supply time point of the Ti raw material are adjusted so that the Mn raw material and the Ti raw material do not coexist in the molten steel in the vacuum chamber 11.

The molten steel obtained by adjusting the composition as described above is supplied to a continuous casting apparatus, and the steel cast piece is continuously cast.

According to the steel melting method of the present embodiment configured as described above, the Mn raw material is supplied to the molten steel in the vacuum chamber 11 in the molten steel in the vacuum chamber 11 in the secondary refining step. After the supplied Mn raw material has been melted in the molten steel and uniformly dispersed, the Ti raw material is supplied to the molten steel in the vacuum chamber 11, so that the Mn raw material and the Ti raw material do not coexist on the molten steel, and Mn can be suppressed. The composite oxide (MnO, TiO _X ) with Ti is formed. Thereby, formation of a composite oxide (Al ₂ O ₃ , TiO _X ) of Al and Ti having a high melting point can be suppressed, and clogging of the molten steel conveying path can be prevented from occurring, and the predetermined number of continuous continuous castings can be stably performed. Further, it is possible to suppress the inclusion of inclusions, and it is possible to manufacture a high-quality cast piece.

Further, in the method for melting steel according to the embodiment, it is preferable to sequentially supply the Al raw material and the Mn raw material in the secondary refining step, that is, in the order of the Al raw material, the Mn raw material, and the Ti raw material in the secondary refining step. Supply to molten steel. In this case, as described in the first embodiment, formation of a composite oxide (MnO, Al ₂ O ₃ ) of Mn and Al is avoided, and formation of a composite oxide (MnO, TiO _x ) of Mn and Ti is avoided. It can more reliably prevent the molten steel conveying path from being blocked.

In the above, the method of melting the steel according to the embodiment of the present invention has been specifically described. However, the present invention is not limited thereto, and can be appropriately modified without departing from the scope of the invention. For example, although the present embodiment is described using a treatment furnace composed of a vacuum chamber, the present invention is not limited thereto, and the present invention can be applied to a treatment furnace capable of performing secondary refining.

EXAMPLES Hereinafter, the experimental results that have been carried out will be described to confirm the effects of the present invention. A steel slab was produced by casting a molten steel having a composition shown in Table 1 in a vertical bending type continuous casting machine (hereinafter referred to as a continuous casting machine). Further, the steel type 2 of Table 1 was an extremely low carbon material, and the undeoxidized tapping was performed in a converter, and the oxygen in the molten steel was about 500 ppm after the decarburization treatment with RH and before the supply of the Al raw material and the supply of the Mn raw material.

[Table 1]

Table 2 shows the supply time points of the Al raw material, the Mn raw material, and the Ti raw material in the secondary refining step.

[Table 2]

In each of the experimental examples, the nozzle clogging condition (casting condition) at the time of performing 8 continuous casting was evaluated based on the following criteria. A: 8 Example of the tendency of nozzle clogging in any continuous feeding in continuous casting. B: 8 continuous continuous casting, the tendency of nozzle clogging was observed only in one feeding C: 8 continuous In the continuous casting, an example of the tendency of nozzle clogging was observed only in two feedings: In the continuous casting of 8 times, an example of the tendency of nozzle clogging was observed in three or more feedings (Comparative Example) E: 8 continuous In the case of continuous casting, there is an example in which nozzle clogging occurs. (Comparative Example) The example of "the tendency to observe the clogging of the nozzle" refers to the cross-sectional area of the nozzle without deposits before the start of casting, and the inclusion of the deposit after the casting is completely completed. An example in which the nozzle cross-sectional area ratio is 95% or less, and "an example of occurrence of nozzle clogging" means a cross-sectional area of a nozzle having no deposits before starting casting, and a nozzle cross-sectional area ratio of adhering matter after the casting is completely finished is 75%. The following example.

[table 3]

In Experimental Examples 1 to 6 in which the appropriate raw material supply time was used, it was confirmed that the nozzle was suppressed from being clogged. It is presumed that this is because the composite of Mn and Al (MnO, Al ₂ O ₃ ) and/or Mn and Ti is suppressed by avoiding the coexistence of the Mn raw material and the Al raw material and/or avoiding the coexistence of the Mn raw material and the Ti raw material. Since the oxide (MnO, TiO _X ) is formed, the formation of a composite oxide (Al ₂ O ₃ , TiO _X ) of Al and Ti having a high melting point is suppressed.

On the other hand, in Experimental Examples 7 and 8, the tendency of nozzle clogging was observed in three or more additions. It is presumed that MnO is produced by supplying Mn raw material first, and then Al raw material is supplied thereto. Therefore, a composite oxide of Mn and Al (MnO·Al ₂ O ₃ ) is formed, thereby forming a composite oxidation of Al and Ti having a high melting point. Caused by (Al ₂ O ₃ , TiO _X ).

Further, in Experimental Examples 9 and 10, nozzle clogging occurred during the casting. It is estimated that a composite oxide of Mn and Al (MnO·Al ₂ O ₃ ) and a composite oxide of Mn and Ti (MnO·TiO _X ) are formed, and a composite oxide of Al and Ti having a high melting point is formed ( Al ₂ O ₃ · TiO _X ).

From the above, it can be confirmed that, according to the present invention, it is possible to provide a method for melting steel which can stably perform casting even when continuously casting an Al deoxidized steel containing Mn and Ti while suppressing the clogging of the molten steel conveying path. .

Industrial Applicability According to the present invention, even when the Al deoxidized steel containing Mn and Ti is continuously cast, the clogging of the molten steel conveying path can be suppressed, and the casting can be stably performed.

10‧‧‧Processing furnace

11‧‧‧vacuum tank

12‧‧‧Exhaust Department

13‧‧‧Sipper

14‧‧‧Inert gas introduction mechanism

15‧‧‧Draining tube

17‧‧‧ Element Supply Department

Fig. 1 is an explanatory view of a treatment furnace (vacuum tank) used in a method for melting steel according to an embodiment of the present invention. Fig. 2 is an explanatory diagram of a time point at which oxygen is blown.

Claims (11)

A method for melting steel is a method for melting steel composed of Al deoxidized steel containing Mn and Ti, and the method for melting the steel is characterized by comprising the following steps: one refining step, and one refining in a converter; And a secondary refining step of transferring the molten steel from the converter to the processing furnace, and supplying the Al raw material, the Mn raw material, and the Ti raw material to the molten steel in the processing furnace to adjust a composition, wherein the secondary refining step is Providing the step of supplying the Al raw material to the molten steel in the processing furnace, and then sequentially or simultaneously supplying the Mn raw material and supplying the Ti raw material; or sequentially or simultaneously supplying the molten steel in the processing furnace The Al raw material and the Mn raw material are supplied, and then the Ti raw material is supplied. The method for melting steel according to claim 1, wherein in the secondary refining step, the Al raw material is supplied, and then the Mn raw material is supplied sequentially or simultaneously and the Ti raw material is supplied. The method for melting a steel according to claim 2, wherein the supply of the Mn raw material is started after 30 seconds or more has elapsed after the supply of the Al raw material is completely completed. The method for melting a steel according to claim 2 or 3, wherein in the secondary refining step, the Al raw material is supplied, and then the Mn raw material is supplied in sequence and supplied The aforementioned Ti raw material is given. The method for melting steel according to claim 4, wherein the supply of the Ti raw material is started after 30 seconds or more has elapsed after the supply of the Mn raw material is completely completed. In the method for melting steel according to claim 2 or 3, when the Al raw material is supplied to the molten steel, the oxygen in the molten steel is 150 ppm or more by mass. The method for melting steel according to claim 1, wherein in the secondary refining step, the Al raw material is supplied sequentially or simultaneously, and the Mn raw material is supplied, and then the Ti raw material is supplied. The method for melting steel according to claim 7, wherein the supply of the Ti raw material is started after 30 seconds or more has elapsed after the supply of the Mn raw material is completely completed. A method of melting a steel according to any one of claims 1, 2, 3, 7, or 8, wherein the oxygen is blown in the secondary refining step. The method for melting steel according to claim 9, wherein the oxygen is not blown during the period from 1 minute before the supply of the Al raw material is started to one minute after the supply of the Al raw material is completed; A period from 1 minute before the supply of the Mn raw material to the end of the Mn raw material, and a period from 1 minute before the supply of the Ti raw material to the end of the supply of the Ti raw material. The method for melting a steel according to any one of claims 1, 2, 3, 7, or 8, wherein the aforementioned secondary refining step is completely finished, the aforementioned molten steel The mass ratio includes: C: 0.0013% or more and 0.040% or less, Al: 0.01% or more and 0.10% or less, Mn: 0.20% or more and 3.00% or less, and Ti: 0.004% or more and 0.100% or less.