JP6007887B2 - Vacuum degassing apparatus and method for decarburizing molten steel using the same - Google Patents

Description

  The present invention relates to a vacuum degassing apparatus for decarburizing molten steel and a method for decarburizing molten steel using the same.

  Conventionally, in a steelmaking process, a vacuum degassing apparatus that performs decarburization processing of molten steel has been used. For example, the RH vacuum degassing apparatus immerses two dip tubes leading to the inside of the vacuum vessel in molten steel in the ladle, and between these ladles and the vacuum vessel via these two dip tubes. The molten steel is exposed to a reduced pressure space (vacuum) in the vacuum chamber while circulating the molten steel. Thereby, a RH vacuum degassing apparatus performs the decarburization process which reduces the carbon concentration in molten steel.

  As a conventional technique related to the decarburization treatment of molten steel, for example, by using information on exhaust gas discharged from a vacuum tank accompanying decarburization treatment of molten steel, the carbon concentration contained in the molten steel during decarburization treatment (hereinafter, There is an RH vacuum degassing device that estimates the molten steel carbon concentration and terminates the decarburization treatment of the molten steel when the estimated value of the obtained molten carbon concentration reaches a target value (see Patent Documents 1 and 2). . Also, a molten steel sample is collected during the estimation of the molten steel carbon concentration based on the exhaust gas information, etc., and based on the analytical value of the collected molten steel sample, the molten steel carbon concentration is considered in consideration of information detection and analysis delay time. There is an RH vacuum degassing apparatus that obtains an estimated value and terminates the decarburization process of the molten steel when the estimated value reaches the target value of the molten steel carbon concentration (see Patent Document 3).

JP-A-9-202913 Japanese Patent No. 2985643 JP 11-279625 A

  On the other hand, in the actual operation of the decarburization treatment of molten steel, the inner wall of the dip tube that communicates between the ladle and the vacuum chamber is worn due to the recirculation of the molten steel between the ladle and the vacuum chamber. In many cases, the adhesion of the alloy to the inner wall proceeds and the inner diameter of the dip tube changes during the decarburization treatment of the molten steel. However, in the above-described conventional technology, when the inner diameter of the dip tube changes during the decarburization treatment of the molten steel, the estimation accuracy of the molten steel carbon concentration is lowered, and as a result, an appropriate molten steel carbon concentration satisfying the standard is obtained. It becomes difficult to finish the decarburization process of the molten steel at the timing. Further, as disclosed in Patent Document 3, when the molten steel carbon concentration is estimated based on the analysis value of the collected molten steel sample, the time required for obtaining the analysis result of the molten steel sample is the time required for decarburizing the molten steel. May be excessively long.

  This invention is made | formed in view of said situation, Comprising: The estimation precision of molten steel carbon concentration can be improved, and the decarburization process of molten steel is complete | finished at an appropriate timing based on the estimated value of molten steel carbon concentration An object of the present invention is to provide a vacuum degassing apparatus that can be used and a method for decarburizing a molten steel using the same.

  In order to solve the above-described problems and achieve the object, a vacuum degassing apparatus according to the present invention has a dip tube immersed in molten steel in a ladle, and passes through the dip tube under a reduced pressure lower than atmospheric pressure. A vacuum chamber that sucks the molten steel from the ladle to decarburize the molten steel, and a ring of the molten steel that circulates between the ladle and the vacuum chamber through the dip tube during the decarburization process. The flow rate is calculated by taking into account the inner diameter change of the dip tube accompanying the reflux of the molten steel, the calculated annular flow rate of the molten steel, the material balance equation regarding the carbon in the molten steel in the decarburization treatment, and the molten steel Based on the decarburization rate and the reaction model equation in the tank representing the decarburization reaction of the molten steel in the vacuum tank, the carbon concentration in the molten steel is estimated, and the estimated carbon concentration becomes a predetermined target value. And a controller that terminates the decarburization process at a timing reached. Characterized in that was.

  Further, the vacuum degassing apparatus according to the present invention further includes a temperature concentration measuring unit that measures the temperature of the molten steel and the oxygen concentration in the molten steel in the above invention, and the control unit includes the mass balance equation Based on the estimation formula of the carbon concentration in the molten steel derived based on the calculation formula of the decarburization rate and the reaction model equation in the tank, the temperature of the molten steel, the oxygen concentration, and the ring flow rate of the molten steel are used. The carbon concentration in the molten steel is estimated.

  Further, the vacuum degassing apparatus according to the present invention, in the above invention, performs an exhaust gas flow meter for measuring a flow rate of exhaust gas discharged from the vacuum tank during the decarburization process, and performs component analysis of the exhaust gas. An exhaust gas component analyzer that measures the carbon monoxide concentration and the carbon dioxide concentration in the exhaust gas, and the control unit uses the flow rate of the exhaust gas, the carbon monoxide concentration, and the carbon dioxide concentration. Calculating the decarburization speed of the molten steel, determining whether the calculated decarburization speed is equal to or lower than a predetermined speed, and if the decarburization speed is equal to or lower than the predetermined speed, the carbon concentration in the molten steel is calculated. It is characterized by estimating.

  Moreover, the decarburization processing method for molten steel according to the present invention includes immersing a dip tube of a vacuum tank in molten steel in a ladle, and the ladle and the vacuum tank through the dip tube under a reduced pressure lower than atmospheric pressure. In the molten steel decarburization processing method using a vacuum degassing apparatus that performs decarburization processing of the molten steel while circulating the molten steel between, the annular flow rate of the molten steel between the ladle and the vacuum tank is Calculated by taking into account the inner diameter change of the dip tube accompanying the circulating flow of molten steel, the calculated annular flow rate of the molten steel, the material balance equation regarding the carbon in the molten steel in the decarburization treatment, the decarburization rate of the molten steel, Based on the reaction model equation in the tank representing the decarburization reaction of the molten steel in the vacuum tank, the molten steel carbon concentration estimation step for estimating the carbon concentration in the molten steel and the molten steel carbon concentration estimation step were estimated. The carbon concentration is a predetermined value. Characterized in that it comprises a decarburization end step to end the decarburization to the timing value has been reached, the.

  Moreover, the decarburization treatment method for molten steel according to the present invention further includes a temperature concentration measuring step for measuring the temperature of the molten steel and the oxygen concentration in the molten steel in the above invention, and the molten steel carbon concentration estimating step includes: Based on the estimation formula for the carbon concentration in the molten steel derived based on the mass balance equation, the decarburization rate calculation equation, and the reaction model equation in the tank, the temperature of the molten steel, the oxygen concentration, and the molten steel The carbon concentration in the molten steel is estimated using the ring flow rate.

  Moreover, the decarburization treatment method for molten steel according to the present invention includes, in the above invention, an exhaust gas flow rate measuring step for measuring a flow rate of exhaust gas discharged from the vacuum tank during the decarburization treatment, and component analysis of the exhaust gas. Using the exhaust gas component concentration measuring step for measuring the carbon monoxide concentration and the carbon dioxide concentration in the exhaust gas, and the flow rate of the exhaust gas, the carbon monoxide concentration, and the carbon dioxide concentration. A decarburization speed calculation step for calculating a charcoal speed; and a determination step for determining whether or not the decarburization speed calculated by the decarburization speed calculation step is equal to or lower than a predetermined speed, and the molten steel carbon concentration estimation The step is characterized by estimating a carbon concentration in the molten steel when the decarburization speed is equal to or lower than the predetermined speed.

  ADVANTAGE OF THE INVENTION According to this invention, the estimation precision of molten steel carbon concentration can be improved and there exists an effect that the decarburization process of molten steel can be complete | finished at an appropriate timing based on the estimated value of molten steel carbon concentration.

FIG. 1 is a diagram illustrating a configuration example of a vacuum degassing apparatus according to an embodiment of the present invention. FIG. 2 is a diagram illustrating the correlation between the estimated value of the molten steel carbon concentration in the decarburization treatment of molten steel and the inner diameter of the dip tube in the vacuum chamber. FIG. 3 is a flowchart showing an example of a method for decarburizing molten steel according to the embodiment of the present invention.

  Exemplary embodiments of a vacuum degassing apparatus and a method for decarburizing molten steel using the same according to the present invention will be described below in detail with reference to the accompanying drawings. Note that the present invention is not limited to the embodiment. Moreover, in each drawing, the same code | symbol is attached | subjected to the same component.

(Vacuum degasser)
First, a vacuum degassing apparatus according to an embodiment of the present invention will be described. FIG. 1 is a diagram illustrating a configuration example of a vacuum degassing apparatus according to an embodiment of the present invention. The vacuum degassing apparatus 1 according to the present embodiment is an RH type vacuum degassing apparatus having two dip tubes immersed in molten steel 16. Specifically, as shown in FIG. 1, the vacuum degassing apparatus 1 includes a ladle 2 that contains molten steel 16, and an ascending-side dip tube 3 a and a descending-side dip tube 3 b that are immersed in the molten steel 16 in the ladle 2. And a vacuum exhaust device 4 for reducing the pressure in the vacuum chamber 3. Further, the vacuum degassing apparatus 1 includes a circulating gas supply pipe 5 for circulating the molten steel 16 between the ladle 2 and the vacuum tank 3, a circulating gas gas valve 6, and a circulating gas flow meter 7. And a deoxidizing material charging unit 8 for ending the decarburization process of the molten steel 16. Furthermore, the vacuum degassing apparatus 1 includes an in-vessel vacuum gauge 9 that measures the pressure in the vacuum chamber 3, an exhaust gas flow meter 10 that measures the exhaust gas flow rate from the vacuum chamber 3, and an exhaust gas component that performs exhaust gas component analysis. The analyzer 11 includes a measurement probe 12 that measures the temperature of the molten steel 16 and the oxygen concentration in the molten steel 16, an input unit 13, a storage unit 14, and a control unit 15.

  The ladle 2 accommodates the molten steel 16 refined by a converter (not shown) or the like. The ladle 2 containing the molten steel 16 moves to a position on the lower side of the vacuum chamber 3 and rises toward the vacuum chamber 3 so that the ascending-side dip tube 3a and the descending-side dip tube 3b of the vacuum chamber 3 are moved. It is immersed in this molten steel 16. In the present embodiment, the molten steel 16 contains oxygen necessary for decarburizing the molten steel 16 by the vacuum degassing apparatus 1 as dissolved oxygen. That is, when the molten steel 16 is decarburized, it is not necessary to blow and supply oxygen to the surface of the molten steel 16 in the vacuum chamber 3. Further, when oxygen for decarburizing the molten steel 16 is insufficient, oxygen may be supplied to the molten steel 16 from an oxygen supply mechanism (not shown) such as an upper blowing lance.

  The vacuum chamber 3 is for performing the decarburization process of the molten steel 16 under a reduced pressure lower than the atmospheric pressure. Specifically, as shown in FIG. 1, the vacuum chamber 3 has two dip pipes immersed in the molten steel 16 in the ladle 2, that is, an ascending-side dip pipe 3 a and a descending-side dip pipe 3 b at the lower part. Has an exhaust pipe 3c at the top. The vacuum chamber 3 discharges the gas in the vacuum chamber 3 from the exhaust pipe 3c by evacuation or the like, thereby forming a decompressed space lower than the atmospheric pressure. This decompression space is, for example, a substantially vacuum space having a degree of vacuum equal to or greater than a predetermined value. The vacuum chamber 3 forms this decompression space when the ascending-side dip tube 3a and the descending-side dip tube 3b are immersed in the molten steel 16 in the pan 2, and rises under the pressure state of this decompression space (under decompression). The molten steel 16 is sucked from the ladle 2 through the side dip tube 3a and the descending side dip tube 3b. Next, the vacuum tank 3 decarburizes the molten steel 16 by exposing the molten steel 16 to the reduced pressure space while circulating the molten steel 16 to and from the ladle 2 through the rising side dip tube 3a and the descending side dip tube 3b. I do.

The vacuum exhaust device 4 is a device that discharges gas from the vacuum chamber 3. Specifically, as shown in FIG. 1, the vacuum exhaust device 4 is provided in the exhaust pipe 3 c of the vacuum chamber 3. The vacuum exhaust device 4 evacuates the vacuum chamber 3 through the exhaust pipe 3c, and thereby brings the vacuum chamber 3 into the above-described reduced pressure state (substantially vacuum state). The vacuum exhaust device 4 discharges exhaust gas from the vacuum chamber 3 to the outside of the vacuum degassing device 1 through the exhaust pipe 3c by a suction operation or the like. This exhaust gas is a mixed gas containing a gas generated during the decarburization process of the molten steel 16 performed in the vacuum chamber 3. The generated gas in the decarburization process is a gas containing a carbon component separated from the molten steel 16 by the decarburization process, such as carbon monoxide (CO) and carbon dioxide (CO ₂ ).

  The recirculation gas supply pipe 5 is a recirculation gas supply pipe for recirculating the molten steel 16 between the ladle 2 and the vacuum chamber 3. Specifically, as shown in FIG. 1, the recirculation gas supply pipe 5 is arranged in such a manner that its outlet end is connected to the rising side dip pipe 3 a of the vacuum chamber 3. The recirculation gas supply pipe 5 blows recirculation gas into the molten steel 16 in the ascending-side dip pipe 3a, and the molten steel 16 in the ascending-side dip pipe 3a is taken from the ladle 2 side by the air lift pump action generated thereby. (See the broken line arrow shown in FIG. 1). Along with this, the molten steel 16 in the vacuum chamber 3 is decarburized under reduced pressure and then descends from the vacuum chamber 3 side to the ladle 2 side through the descending side dip tube 3b (see the broken line arrow shown in FIG. 1). The molten steel 16 circulates (circulates) between the ladle 2 and the vacuum chamber 3 through the ascending-side dip tube 3a and the descending-side dip tube 3b. As described above, for example, an inert gas such as argon gas is used as the reflux gas supplied from the reflux gas supply pipe 5 into the ascending-side dip pipe 3a.

  As shown in FIG. 1, the gas valve 6 is an automatic open / close valve that is provided in the circulating gas supply pipe 5 and whose valve opening / closing operation is controlled by the control unit 15. The gas valve 6 performs a valve opening operation based on the control of the control unit 15, thereby enabling the supply of the recirculation gas from the recirculation gas supply pipe 5 into the ascending-side immersing pipe 3 a. Further, the gas valve 6 performs a valve closing operation based on the control of the control unit 15, thereby stopping the supply of the circulating gas.

  The recirculation gas flow meter 7 is connected to the gas valve 6 from a predetermined position of the recirculation gas supply pipe 5, for example, from the outlet end of the recirculation gas supply pipe 5 (connection end to the ascending side immersion pipe 3a) as shown in FIG. Between the two. The recirculation gas flow meter 7 measures the flow rate of the recirculation gas (hereinafter referred to as recirculation gas flow rate) supplied into the ascending-side dip tube 3a through the recirculation gas supply tube 5 and measures the recirculation flow for each time. An electric signal indicating the gas flow rate is transmitted to the control unit 15.

  The deoxidizing material charging unit 8 inputs a deoxidizing material for ending the decarburization processing of the molten steel 16 into the molten steel 16. Specifically, as shown in FIG. 1, the deoxidizing material charging unit 8 is disposed in the vicinity of the opening of the ladle 2. The deoxidizing material charging unit 8 is controlled by the control unit 15 at the timing of supplying the deoxidizing material. The molten steel 16 in the pan 2 is charged. As this deoxidizing material, for example, aluminum (Al) or the like is used.

  The tank vacuum gauge 9 measures the degree of vacuum in the vacuum tank 3. Specifically, as shown in FIG. 1, the in-vessel vacuum gauge 9 is provided at a predetermined position (for example, in the vicinity of the exhaust pipe 3 c) on the upper inner wall of the vacuum chamber 3. The tank vacuum gauge 9 measures the pressure in the vacuum tank 3 (hereinafter referred to as “vacuum tank pressure”), which is reduced by the action of the vacuum exhaust device 4 described above, as the degree of vacuum, and each time, An electric signal indicating the pressure is transmitted to the control unit 15.

  The exhaust gas flow meter 10 measures the flow rate of the exhaust gas discharged from the vacuum chamber 3. Specifically, as shown in FIG. 1, the exhaust gas flow meter 10 is provided at a predetermined position of the exhaust pipe 3 c of the vacuum chamber 3. The exhaust gas flow meter 10 measures the flow rate of exhaust gas discharged from the vacuum chamber 3 to the outside through the exhaust pipe 3c during the decarburization process of the molten steel 16 (hereinafter referred to as exhaust gas flow rate). In each case, an electric signal indicating the measured exhaust gas flow rate is transmitted to the control unit 15.

The exhaust gas component analyzer 11 measures the concentration of carbon component-containing gas in the exhaust gas discharged from the vacuum chamber 3. Specifically, as shown in FIG. 1, the exhaust gas component analyzer 11 is provided at a predetermined position (for example, in the vicinity of the exhaust gas flow meter 10) of the exhaust pipe 3 c of the vacuum chamber 3. The exhaust gas component analyzer 11 performs component analysis of exhaust gas discharged from the vacuum chamber 3 through the exhaust pipe 3c when the molten steel 16 is decarburized. Thereby, the exhaust gas component analyzer 11 measures the carbon component-containing gas concentration in the exhaust gas, specifically, the carbon monoxide concentration and the carbon dioxide concentration. Each time, the exhaust gas component analyzer 11 transmits an electrical signal indicating the measured carbon monoxide concentration (hereinafter referred to as exhaust gas CO concentration) and carbon dioxide concentration (hereinafter referred to as exhaust gas CO ₂ concentration) to the control unit 15. To do.

  The measurement probe 12 functions as a temperature concentration measuring unit that measures the temperature of the molten steel 16 and the oxygen concentration in the molten steel 16. Specifically, the measurement probe 12 is a probe-type measuring instrument in which a temperature detector and an oxygen concentration detector are incorporated in a probe-shaped housing. As shown in FIG. 1, the measurement probe 12 is appropriately immersed in the molten steel 16 in the ladle 2, and the temperature of the molten steel 16 (hereinafter referred to as molten steel temperature) and the oxygen concentration in the molten steel 16 (hereinafter referred to as molten steel oxygen concentration). Measure). Each time, the measurement probe 12 transmits an electrical signal indicating the measured molten steel temperature and molten steel oxygen concentration to the control unit 15.

  The input unit 13 inputs various types of information necessary for arithmetic processing for estimating the carbon concentration in the molten steel 16 to be decarburized to the control unit 15. For example, every time the vacuum degassing apparatus 1 receives the molten steel 16 for one charge accommodated in the ladle 2, the input unit 13 receives the total weight of the molten steel 16 for the received one charge (hereinafter referred to as molten steel weight). Is input to the control unit 15. Further, the input unit 13 inputs various information such as the inner diameter of the dip tube of the vacuum chamber 3 and constants used for calculation processing to the control unit 15. In the present embodiment, the inner diameter of the dip tube of the vacuum chamber 3 is the original inner diameter of the dip tube, such as an unused or inner diameter of the dip tube in equipment specifications. Such an inner diameter of the dip tube may be an inner diameter of at least one of the ascending-side dip tube 3a and the descending-side dip tube 3b of the vacuum chamber 3, or the ascending-side dip tube 3a and the descending-side dip tube 3b. It may be an average value, a maximum value, or a minimum value of each inner diameter.

  The memory | storage part 14 memorize | stores the various information required for the arithmetic processing for estimating the carbon concentration in the molten steel 16 of the decarburization process object. For example, the memory | storage part 14 memorize | stores the correction coefficient etc. which were calculated | required from the past performance data of the molten steel carbon concentration accumulated by the operation of the decarburization process of the various molten steel repeatedly performed in the past using the vacuum degassing apparatus 1. The molten steel carbon concentration is the carbon concentration in the molten steel 16 to be decarburized. The storage unit 14 transmits the information instructed to be read out by the control unit 15 to the control unit 15 from the various pieces of stored information.

  The control unit 15 controls the end timing of the decarburization process of the molten steel 16 by the vacuum degassing apparatus 1. Specifically, the control unit 15 is configured using a memory that stores various types of information such as calculation parameters, a CPU that executes a preset program, and the like. As an arithmetic expression for estimating the carbon concentration (molten steel carbon concentration) in the molten steel 16 to be decarburized, the control unit 15 includes a material balance expression that represents the material balance of the entire system related to carbon in the molten steel 16, and the molten steel. An arithmetic expression representing the decarburization speed in the 16 decarburization process is preset. Further, the control unit 15 includes an arithmetic expression representing the ring flow rate of the molten steel 16 during the decarburization treatment of the molten steel 16, an arithmetic expression representing the carbon flow rate in the exhaust gas from the vacuum chamber 3, and the molten steel in the vacuum chamber 3. A tank reaction model formula representing 16 decarburization reactions is preset. Further, the control unit 15 includes an arithmetic expression that represents an equilibrium constant of the reaction between carbon and oxygen in the decarburization treatment of the molten steel 16, an estimation expression for the molten steel carbon concentration, and an arithmetic expression that represents the amount of change in the dip tube inner diameter for each charge. Expressions are programmed in advance. The control unit 15 includes input signals from the above-described reflux gas flow meter 7, in-vessel vacuum meter 9, exhaust gas flow meter 10, exhaust gas component analyzer 11, and measurement probe 12, and input information from the input unit 13. And the information read from the storage unit 14 are used to perform arithmetic processing based on each arithmetic expression described above.

Specifically, the control unit 15 performs an annular flow rate of the molten steel 16 that flows between the ladle 2 and the vacuum chamber 3 through the ascending-side dip tube 3a and the descending-side dip tube 3b during the decarburization process of the molten steel 16 (hereinafter referred to as “flow rate”). , The flow rate of the molten steel ring) is calculated in consideration of the change in the inner diameter of the dip tube accompanying the circulating flow of the molten steel 16. Further, the control unit 15 calculates the decarburization speed of the molten steel 16 using the exhaust gas flow rate from the vacuum chamber 3, the exhaust gas CO concentration, and the exhaust gas CO ₂ concentration, and the calculated decarburization speed is equal to or less than a predetermined speed. Determine whether or not. When the decarburization speed is equal to or lower than the predetermined speed, the control unit 15 relates to the molten steel ring flow rate calculated by taking into account the change in the inner diameter of the dip tube and the carbon in the molten steel 16 in the decarburization process of the molten steel 16 as described above. The molten steel carbon concentration is estimated based on the material balance equation, the decarburization rate of the molten steel 16, and the reaction model equation in the tank representing the decarburization reaction of the molten steel 16 in the vacuum chamber 3. At this time, the control unit 15 calculates the molten steel temperature of the molten steel 16 based on the estimation formula of the molten carbon concentration derived from the preset mass balance equation, the decarburization rate calculation equation, and the reaction model equation in the tank. The molten steel carbon concentration is estimated using the molten steel oxygen concentration and the molten steel ring flow rate. The control unit 15 ends the decarburization processing of the molten steel 16 by the vacuum degassing apparatus 1 at the timing when the estimated molten steel carbon concentration reaches a predetermined target value.

(Calculation processing required to estimate molten steel carbon concentration)
Next, a calculation process required for estimating the molten steel carbon concentration in the present invention will be described. In the controller 15 of the vacuum degassing apparatus 1 according to the present embodiment, as described above, various arithmetic expressions required for estimating the carbon concentration (molten steel carbon concentration) in the molten steel 16 to be decarburized are previously stored. Is set. Among these various calculation formulas, the mass balance equation representing the mass balance of the entire system related to carbon in the molten steel 16 is the molten steel carbon concentration [C], the molten steel flow rate Q, the molten steel weight W, and the downcomer side molten steel carbon concentration. [C] ^* and is expressed by the following formula (1).

In the above formula (1), d [C] / dt is the amount of change in the molten steel carbon concentration [C] per unit time, and corresponds to the decarburization rate of the molten steel 16 to be decarburized. Further, the downcomer side molten steel carbon concentration [C] ^* is the carbon concentration in the molten steel 16 in the downside dip tube 3b that forms the descending path of the molten steel 16 from the vacuum chamber 3 to the ladle 2 shown in FIG. is there.

On the other hand, among the various arithmetic expressions set in the control unit 15 described above, the arithmetic expression representing the decarburization speed in the decarburization process of the molten steel 16 is the flow rate of the carbon component contained in the exhaust gas from the vacuum chamber 3 (hereinafter, It is expressed by the following equation (2) using G _{C (referred} to as exhaust gas carbon flow rate) and molten steel weight W. Moreover, the arithmetic expression showing the molten steel ring flow rate Q at the time of the decarburization treatment of the molten steel 16 is the flow rate F of the recirculation gas, the dip tube inner diameter d of the vacuum chamber 3, and the change amount of the dip tube inner diameter d for each charge (hereinafter referred to as the flow rate). D _gN ), atmospheric pressure Pa (= 1 [atm]), and vacuum chamber pressure P, and are expressed by the following equation (3).

The exhaust gas carbon flow rate G _C included in the above equation (2) uses the exhaust gas flow rate G from the vacuum chamber 3, the exhaust gas CO concentration [CO], the exhaust gas CO ₂ concentration [CO ₂ ], and a constant a. Is expressed by the following equation (4).

G _C = a · G · ([CO] + [CO ₂ ]) (4)

On the other hand, among the various arithmetic expressions set in the control unit 15 described above, the reaction model expression in the tank representing the decarburization reaction of the molten steel 16 in the vacuum tank 3 is the downcomer-side molten steel carbon concentration [C] ^* and the vacuum. Using the pressure P in the tank, the equilibrium constant K of the reaction between carbon and oxygen in the decarburization treatment of the molten steel 16, the molten steel oxygen concentration [O], the correction coefficient B, and the molten steel carbon concentration [C], It is represented by (5).

In the above equation (5), the correction coefficient B was obtained from past performance data of the molten steel carbon concentration [C] accumulated by the operation of decarburization treatment of various molten steels repeatedly performed using the vacuum degassing apparatus 1 in the past. Correction coefficient. This correction coefficient B is stored in the storage unit 14 shown in FIG. Further, the equilibrium constant K is expressed by the following equation (6) using the molten steel temperature T.

K = exp (2671 / T + 4.612) (6)

  Moreover, the estimation formula of the above-mentioned molten steel carbon concentration [C] includes a mass balance equation such as equation (1), a decarburization rate calculation equation such as equation (2), and a tank such as equation (5). It is derived on the basis of the internal reaction model equation and is expressed as the following equation (7).

In the vacuum degassing apparatus 1 according to the present embodiment, the control unit 15 includes the recirculation gas flow meter 7, the in-tank vacuum meter 9, the exhaust gas flow meter 10, the exhaust gas component analyzer 11, and the measurement probe 12. Using the input signal, the input information from the input unit 13, and the information read from the storage unit 14, arithmetic processing is performed based on the above-described equations (1) to (7). In particular, the control unit 15 takes into account the change in the inner diameter d of the dip tube due to the wear of the inner wall of the dip tube or the adhesion of metal due to the circulation of the molten steel 16 in the calculation process of the equation (3). That is, the control unit 15 uses the value obtained by adding the dip tube inner diameter change d _gN accompanying the reflux of the molten steel 16 to the original dip tube inner diameter d of the vacuum chamber 3 as the dip tube inner diameter in the actual operation of the decarburization treatment of the molten steel 16. Using the estimated value of the dip tube inner diameter in actual operation and the like as an estimated value, the molten steel ring flow rate Q is calculated based on the equation (3). The control unit 15 acquires the molten steel ring flow rate Q calculated in this way as an estimated value of the molten steel ring flow rate in the actual operation of the decarburization process of the molten steel 16. Further, the control unit 15 calculates the exhaust gas carbon flow rate G _C from the vacuum chamber 3 based on the formula (4), and uses the calculated exhaust gas carbon flow rate G _C for the exhaust gas in the actual operation of the decarburization treatment of the molten steel 16. Obtained as an estimate of carbon flow rate. The control unit 15 includes the molten steel ring flow rate Q and the exhaust gas carbon flow rate G _C acquired in this way, the vacuum chamber pressure P from the vacuum gauge 9 in the chamber, the equilibrium constant K according to the equation (6), and the measurement probe 12. The molten steel carbon concentration [C] is calculated on the basis of the equation (7) using the molten steel oxygen concentration [O] from No. 1 and the correction coefficient B read from the storage unit 14. That is, the control unit 15 calculates the molten steel carbon concentration [C] in consideration of the change of the dip tube inner diameter d accompanying the reflux of the molten steel 16. The control unit 15 acquires the molten steel carbon concentration [C] calculated as described above as an estimated value of the molten steel carbon concentration in the actual operation of the decarburization process of the molten steel 16.

(Changes in the inner diameter of the dip tube with the flow of molten steel)
Next, a change in the inner diameter d of the dip tube accompanying the reflux of the molten steel 16 will be described. When performing the decarburization process of the molten steel 16 using the vacuum degassing apparatus 1 shown in FIG. 1, the molten steel 16 for one charge, which is the decarburization target, is, as described above, the ascending-side dip tube 3 a and the descending side. It circulates between the ladle 2 and the vacuum chamber 3 through the dip tube 3b (hereinafter referred to as two dip tubes as appropriate). During the actual operation of the decarburization process, the inner diameters of these two dip pipes increase and decrease with the circulation of the molten steel 16.

  Specifically, when the molten steel 16 circulates between the ladle 2 and the vacuum chamber 3, the molten steel 16 rises through the ascending side dip tube 3a and also passes through the descending side dip tube 3b. Descend. At this time, phenomena such as wear due to passage (circulation) of the molten steel 16 and adhesion of alloy iron added to the molten steel 16 during circulation occur on the inner walls of these two dip tubes. The wear of the inner wall of the dip tube due to the passage of the molten steel 16 through the dip tube (hereinafter referred to as wear in the dip tube due to the molten steel recirculation) increases the inner diameter d of the dip tube of the vacuum chamber 3. On the other hand, the adhesion of the alloy iron to the inner wall of the dip tube when the molten steel 16 passes through the dip tube (hereinafter referred to as the adhesion of the added alloy iron in the dip tube when the molten steel circulates) reduces the dip tube inner diameter d of the vacuum chamber 3.

The increase / decrease change in the inner diameter d of the dip tube accompanying the circulating flow of the molten steel 16 described above affects the estimation of the molten steel carbon concentration [C] in the decarburization treatment of the molten steel 16. FIG. 2 is a diagram illustrating the correlation between the estimated value of the molten steel carbon concentration in the decarburization treatment of molten steel and the inner diameter of the dip tube in the vacuum chamber. In the decarburization process of the molten steel 16, the estimated value of the molten steel carbon concentration [C] changes according to the change of the dip tube inner diameter d of the vacuum chamber 3, as shown in FIG. Therefore, the molten steel carbon concentration [C] in the decarburization treatment of the molten steel 16 should be estimated in consideration of the change of the dip tube inner diameter d accompanying the reflux of the molten steel 16, that is, the dip tube inner diameter change amount d _gN .

In the present invention, the dip tube inner diameter change d _gN accompanying the _circulation of the molten steel 16 is two phenomena that occur on the inner wall of the dip tube during the _circulation of the molten steel 16, specifically, the wear in the dip tube due to the molten steel circulation and the molten steel circulation. It is calculated paying attention to the adhesion of the added alloy iron in the dip tube. That is, the dip tube inner diameter change d _gN is the dip tube wear amount d _a per unit time due to the _circulating flow of the molten steel 16, the dip tube inner diameter reduction amount d _b per unit time due to the addition of the alloy iron of the molten steel 16, and the molten steel reflux. Using the time t _N and the alloy iron addition amount J _N during the reflux of the molten steel 16, it is expressed by the following equation (8). The molten steel reflux time t _N is the time during which the molten steel 16 is circulating between the ladle 2 and the vacuum chamber 3.

d _gN = d _a × t _N −d _b × J _N (8)

Among the terms of the above equation (8), the dip tube inner diameter variation d _gN , the molten steel reflux time t _N , and the alloyed iron addition amount J _N are the results of the decarburization treatment of the molten steel 16 using the vacuum degassing apparatus 1. It can be obtained by using the operation data and the measured inner diameters before and after replacement of the two dip tubes (the rising side dip tube 3a and the descending side dip tube 3b) to be exchanged every time the molten steel 16 is charged. Specifically, each inner diameter measurement value in the unused state (state immediately after replacement) of the two dip pipes exchanged after the previous decarburization process of the molten steel 16 is completed, and the current decarburization process of the molten steel 16 is completed. After that, the measured values of the inner diameter change d _gN of the dip tube are obtained by using the measured values of the inner diameters of the two dip tubes to be replaced after use (the state immediately before the replacement) and taking the difference between the measured values of the inner diameters. A value is obtained. Further, the elapsed time from the start of using the two dip pipes this time for the circulation of the molten steel 16 to the end of the use is measured as the molten steel circulation time t _N. Further, the amount of alloy iron added to the molten steel 16 in the reflux when the two dip tubes this time are used for the reflux of the molten steel 16 is actually measured as the alloy iron addition amount J _N.

The above-described measurement of the inner diameter of the dip tube, the time measurement of the molten steel reflux, and the measurement of the amount of addition of alloy iron are performed N times (N is a positive integer), and the dip tube inner diameter change d _{gN as the} Nth measurement result. And the molten steel reflux time t _N and the alloy iron addition amount J _N are substituted into the equation (8). As a result, the equation (8) becomes a linear function equation having the dip tube wear amount d _a and the dip tube inner diameter reduction amount d _b as two variables. As described above, the two variables described above correspond to each of the inner diameter measurement of the dip tube performed N times (N = 1, 2, 3,...), The time measurement of the molten steel reflux, and the addition amount measurement of the iron alloy. N linear function equations are derived. Based on these N linear function equations, an optimum dip tube wear amount d _a and dip tube inner diameter reduction amount d _b are obtained by the least square method. The optimum dip tube wear d _a and dip tube inner diameter reduction d _b obtained in this way are substituted into the above-described equation (8). As a result, the equation (8) shows that the dip tube inner diameter d _a and the dip tube inner diameter decrease d _b are used as coefficients, and the molten steel reflux time t _N and the alloy iron addition amount J _N are variables. This is an arithmetic expression for calculating the change amount d _gN . The dip tube inner diameter change amount d _gN represented by the equation (8) is a change amount of the dip tube inner diameter d associated with the recirculation of the molten steel 16 for one charge, as shown in the above-described equation (3). And included in the calculation formula of the flow rate Q of the molten steel ring. That is, the equation (3) including the term (d + d _gN ) obtained by adding the dip tube inner diameter variation d _gN to the original dip tube inner diameter d of the vacuum chamber 3 is the dip tube inner diameter d accompanying the reflux of the molten steel 16 for one charge. This is an arithmetic expression for calculating the flow rate Q of the molten steel ring in consideration of the change (change in the inner diameter of the dip tube for each charge). Note that the molten steel reflux time t _N and the alloy iron addition amount J _N as variables of the equation (8) are input to the control unit 15 every time the molten steel 16 is charged by the input unit 13 shown in FIG.

(Method for decarburizing molten steel)
Below, the decarburization processing method of the molten steel concerning embodiment of this invention is demonstrated. FIG. 3 is a flowchart showing an example of a method for decarburizing molten steel according to the embodiment of the present invention. In the molten steel decarburizing treatment method according to the present embodiment, the two dip tubes of the vacuum chamber 3 are immersed in the molten steel 16 in the ladle 2 and are taken through these two dip tubes under a reduced pressure lower than the atmospheric pressure. Step S101 shown in FIG. 3 is performed every time the molten steel 16 is charged using the vacuum degassing apparatus 1 (see FIG. 1) that performs the decarburization process of the molten steel 16 while circulating the molten steel 16 between the pan 2 and the vacuum chamber 3. To S109 are sequentially performed.

  That is, in the molten steel decarburizing method according to the present embodiment, the vacuum degassing apparatus 1 first starts decarburizing processing of the molten steel 16 for one charge as shown in FIG. 3 (step S101). In step S <b> 101, the vacuum degassing apparatus 1 receives the molten steel 16 for one charge accommodated in the ladle 2. Next, the vacuum chamber 3 immerses two dip tubes, that is, the ascending side dip tube 3 a and the descending side dip tube 3 b in the molten steel 16 in the ladle 2. In this state, the control unit 15 controls the vacuum exhaust device 4 so as to suck the internal gas in the vacuum chamber 3 and discharge it to the outside. The vacuum evacuation device 4 discharges the internal gas of the vacuum chamber 3 from the exhaust pipe 3c to the outside based on the control of the control unit 15, thereby reducing the pressure in the vacuum chamber 3 to a substantially vacuum state. As a result, the molten steel 16 in the ladle 2 is sucked into the vacuum chamber 3 through the ascending side dip tube 3a and the descending side dip tube 3b. At this timing, the control unit 15 causes the gas valve 6 to perform a valve opening operation. Accordingly, the reflux gas supply pipe 5 supplies the reflux gas to the molten steel 16 in the ascending-side dip pipe 3a. Due to the air lift pump action caused by this, the molten steel 16 rises from the ladle 2 side to the vacuum chamber 3 side through the ascending side dip tube 3a. The molten steel 16 in the vacuum chamber 3 is decarburized under a reduced pressure lower than the atmospheric pressure. The molten steel 16 in the vacuum chamber 3 descends from the vacuum chamber 3 side to the ladle 2 side through the descending side dip tube 3b. In this way, the molten steel 16 is continuously exposed to the reduced pressure space in the vacuum chamber 3 while continuously circulating between the ladle 2 and the vacuum chamber 3 through the ascending-side dip tube 3a and the descending-side dip tube 3b. Decarburized.

  Subsequently, the vacuum degassing apparatus 1 measures the exhaust gas flow rate G from the vacuum chamber 3 (step S102). In step S102, the exhaust gas flow meter 10 measures the flow rate of exhaust gas discharged from the vacuum chamber 3 to the outside through the exhaust pipe 3c when the molten steel 16 is decarburized. The exhaust gas flow meter 10 transmits an electrical signal indicating the measured exhaust gas flow rate G to the control unit 15.

Next, the vacuum degassing apparatus 1 measures the carbon monoxide (CO) concentration and the carbon dioxide (CO ₂ ) concentration in the exhaust gas from the vacuum chamber 3 (step S103). In step S103, the exhaust gas component analyzer 11 performs a component analysis of the exhaust gas discharged from the vacuum chamber 3 through the exhaust pipe 3c when the molten steel 16 is decarburized. Based on the result of this component analysis, the exhaust gas component analyzer 11 measures the carbon monoxide concentration (exhaust gas CO concentration [CO]) and carbon dioxide concentration (exhaust gas CO ₂ concentration [CO ₂ ]) in the exhaust gas. . The exhaust gas component analyzer 11 transmits an electrical signal indicating the measured exhaust gas CO concentration [CO] and exhaust gas CO ₂ concentration [CO ₂ ] to the control unit 15.

Next, the vacuum degassing apparatus 1 calculates the decarburization speed of the molten steel 16 using the measured exhaust gas flow rate G, exhaust gas CO concentration [CO], and exhaust gas CO ₂ concentration [CO ₂ ] (step S104). In step S < _b > 104, the control unit 15 controls the exhaust gas flow rate G based on the input signal from the exhaust gas flow meter 10 and the exhaust gas CO concentration [CO] and exhaust gas CO ₂ concentration [CO ₂ ] based on the input signal from the exhaust gas component analyzer 11. And get. Control unit 15, using the obtained exhaust gas flow rate G and the exhaust gas CO concentration [CO] and flue gas CO ₂ concentration [CO _2], calculates the exhaust carbon flow rate G _C according to equation (4). Next, the control unit 15 uses the calculated exhaust gas carbon flow rate G _C and the molten steel weight W input by the input unit 13 to calculate the decarburization speed d [C] / dt of the molten steel 16 based on the equation (2). calculate.

  Subsequently, the vacuum degassing apparatus 1 determines whether or not the decarburization speed d [C] / dt of the molten steel 16 calculated in step S104 is equal to or lower than a predetermined speed (step S105). In step S105, the control unit 15 compares the decarburization speed d [C] / dt calculated based on Expression (2) as described above with a predetermined speed set in advance. When the control unit 15 determines that the decarburization speed d [C] / dt exceeds the predetermined speed (No at Step S105), the vacuum degassing apparatus 1 returns to Step S102 described above, and the processing steps after Step S102 repeat.

  On the other hand, when the control unit 15 determines that the decarburization speed d [C] / dt is equal to or lower than the predetermined speed (step S105, Yes), the vacuum degassing apparatus 1 sets the molten steel temperature T and the molten steel oxygen concentration [O]. Measurement is performed (step S106). In step S106, the measurement probe 12 is driven based on the control of the control unit 15, and measures the molten steel temperature T and the molten steel oxygen concentration [O]. At this time, the measurement probe 12 is immersed in the molten steel 16 in the ladle 2 and measures the temperature of the molten steel 16 (molten steel temperature T) and the oxygen concentration in the molten steel 16 (molten steel oxygen concentration [O]). . The measurement probe 12 transmits an electrical signal indicating the measured molten steel temperature T and molten steel oxygen concentration [O] to the control unit 15.

Next, the vacuum degassing apparatus 1 estimates the molten steel carbon concentration [C] in consideration of the change in the dip tube inner diameter d of the vacuum chamber 3 accompanying the reflux of the molten steel 16 (step S107). In step S107, the control unit 15 uses the molten steel recirculation time t _N input by the input unit 13 and the alloy iron addition amount J _N during the recirculation of the molten steel 16, and the recirculation of the molten steel 16 based on the equation (8). The dip tube inner diameter change amount d _gN is calculated. The control unit 15 then calculates the calculated dip tube inner diameter change d _gN , the dip tube inner diameter d input by the input unit 13, the _{recirculation} gas flow rate F measured by the recirculation gas flow meter 7, and the tank The molten steel ring flow rate Q between the ladle 2 and the vacuum chamber 3 is calculated based on the equation (3) using the vacuum chamber internal pressure P measured by the internal vacuum gauge 9 and the atmospheric pressure Pa. Thereby, the control part 15 calculates the molten steel ring flow volume Q in consideration of the change of the immersion pipe inner diameter d accompanying the reflux of the molten steel 16. Thereafter, the control unit 15 calculates the calculated molten steel ring flow rate Q, the material balance equation (equation (1)) regarding the carbon in the molten steel 16 in the decarburization process of the molten steel 16, and the decarburization speed d [C] / The carbon concentration in the molten steel 16 is estimated based on dt and a reaction model equation (equation (5)) representing the decarburization reaction of the molten steel 16 in the vacuum chamber 3. At this time, the control unit 15 calculates the molten steel carbon concentration derived from the mass balance equation of the equation (1), the decarburization rate calculation equation of the equation (2), and the reaction model equation in the tank of the equation (5) [ Based on the estimation formula (formula (7)) of C], the carbon concentration in the molten steel 16 is estimated using the molten steel temperature T, the molten steel oxygen concentration [O], and the molten steel ring flow rate Q. Specifically, the control unit 15 calculates the equilibrium constant K of the reaction between carbon and oxygen in the decarburization process of the molten steel 16 based on the equation (6) using the molten steel temperature T measured in step S106. Subsequently, the control unit 15 calculates the molten steel ring flow rate Q and the equilibrium constant K calculated as described above, the pressure P in the vacuum chamber from the vacuum gauge 9 in the tank, and the molten steel oxygen concentration [O] measured in step S106. Then, using the correction coefficient B read from the storage unit 14 and the exhaust gas carbon flow rate G _C , the molten steel carbon concentration [C] is calculated based on the equation (7). In this processing, the control unit 15, the decarburization speed d [C] / dt is used exhaust carbon flow rate G _C when satisfying the condition that is less than a predetermined speed. Through the above arithmetic processing, the control unit 15 calculates the estimated molten steel carbon concentration [C] by taking into account the change in the dip tube inner diameter d accompanying the reflux of the molten steel 16.

  After executing Step S107, the vacuum degassing apparatus 1 determines whether or not the molten steel carbon concentration [C] estimated in Step S107 has reached the target value (Step S108). In step S108, the control unit 15 compares the molten steel carbon concentration [C] (estimated value) calculated based on the equation (7) as described above with the target carbon concentration (target value) in the molten steel 16. To process. The control unit 15 presets a target value of the carbon concentration according to the required specifications of the molten steel 16 based on, for example, order information of the molten steel 16 input by the input unit 13. As a result of this comparison processing, when the control unit 15 determines that the molten steel carbon concentration [C] has not reached the target value (No at Step S108), the vacuum degassing apparatus 1 returns to Step S106 described above, and this step The processing steps after S106 are repeated as appropriate.

  On the other hand, when the control unit 15 determines that the molten steel carbon concentration [C] has reached the target value (step S108, Yes), the vacuum degassing apparatus 1 ends the decarburization process of the molten steel 16 (step S109). In step S109, the control part 15 performs various control operation | movement which complete | finishes the decarburization process of the molten steel 16 at the timing when the molten steel carbon concentration [C] estimated by step S107 reached the target value mentioned above. Specifically, the control unit 15 controls the deoxidizing material feeding unit 8 so as to feed the deoxidizing material into the molten steel 16, and the decarburizing process of the molten steel 16 is terminated through this control. In addition to this, the control unit 15 controls the vacuum exhaust device 4 to stop the suction operation of the internal gas in the vacuum chamber 3, thereby returning the pressure in the vacuum chamber 3 to atmospheric pressure. Further, the control unit 15 causes the gas valve 6 to perform the valve closing operation, and thereby stops the supply of the recirculation gas from the recirculation gas supply pipe 5 into the ascending-side dip pipe 3a.

(Example)
Next, examples of the present invention will be described. In this example, the vacuum degassing apparatus 1 shown in FIG. 1 was used, and the decarburization process of the molten steel 16 was performed along each processing step of steps S101 to S109 shown in FIG. Under the present circumstances, the molten steel carbon concentration [C] in the case of the decarburization process of the molten steel 16 was estimated by performing arithmetic processing based on Formula (1)-(8) mentioned above. In particular, the amount of change in the dip tube inner diameter d of the vacuum chamber 3 accompanying the reflux of the molten steel 16 between the ladle 2 and the vacuum chamber 3 (the dip tube inner diameter change amount d _gN ) is calculated based on the equation (8). The molten steel ring flow rate Q was calculated by applying the calculated dip tube inner diameter change d _gN to the equation (3). In this way, the molten steel ring flow rate Q including the dip tube inner diameter variation d _gN was applied to the equation (7), and the estimated value of the molten steel carbon concentration [C] at the end of the decarburization treatment of the molten steel 16 was calculated.

On the other hand, as a comparative example with respect to the present example, the molten steel carbon concentration [C] was estimated without taking into account the amount of change in the dip tube inner diameter d of the vacuum chamber 3 accompanying the above-described reflux of the molten steel 16. That is, the term of the dip tube inner diameter change amount d _gN is removed from the equation (3), thereby calculating the molten steel ring flow rate Q with the dip tube inner diameter d being a constant value regardless of the circulation of the molten steel 16, and this molten steel ring. The estimated value of the molten steel carbon concentration [C] at the end of the decarburization treatment of the molten steel 16 was calculated by applying the flow rate Q to the equation (7). The conditions of the comparative example were the same as those of this example except that the molten steel carbon concentration [C] was estimated without taking into account the amount of change in the dip tube inner diameter d.

  A portion of the molten steel 16 after the decarburization treatment by the vacuum degassing apparatus 1 was taken as a sample, and the molten steel carbon concentration [C] of this sample was measured. Table 1 shows a comparison result between the actually measured value of the molten steel carbon concentration [C] and each estimated value of the molten steel carbon concentration [C] in the present example and the comparative example.

As shown in Table 1, the estimated value of the molten steel carbon concentration [C] according to this example is higher than the estimated value of the molten steel carbon concentration [C] according to the comparative example. The value was close to the actual measured value. Therefore, by adding the dip tube inner diameter variation d _gN accompanying reflux of molten steel 16, the estimation accuracy of the molten steel carbon concentration at the time of decarburization treatment of the molten steel 16 [C], the dip tube inner diameter variation d _gN It has become clear that it can be improved as compared with the case where no is added.

  As described above, in the embodiment of the present invention, the dip tube of the vacuum vessel is immersed in the molten steel in the ladle, and between the ladle and the vacuum vessel through the dip tube under a reduced pressure lower than the atmospheric pressure. When the molten steel is decarburized while circulating the molten steel, the molten steel ring flow rate between the ladle and the vacuum chamber is calculated taking into account the inner diameter change of the dip tube accompanying the molten steel circulation, and this calculated molten steel ring Based on the flow rate, the mass balance equation for carbon in the molten steel in the decarburization process, the decarburization rate of the molten steel, and the reaction model in the tank representing the decarburization reaction of the molten steel in the vacuum tank, Then, the decarburization process of the molten steel is finished at a timing when the estimated molten steel carbon concentration reaches a predetermined target value.

  For this reason, taking into account the amount of change in the inner diameter of the dip tube that is expected to change as the molten steel circulates, the dip tube inner diameter at the time of processing is corrected to be closer to the actual dip tube inner diameter. Then, the estimated value of the molten steel carbon concentration can be calculated according to the corrected dip tube inner diameter. As a result, compared to the conventional technology that estimates the molten steel carbon concentration by fixing the inner diameter of the dip tube, the estimated value of the molten steel carbon concentration is close to the actual value of the molten steel carbon concentration in the actual operation of the decarburization treatment of the molten steel. Can be obtained. As a result, it is possible to improve the estimation accuracy of the molten steel carbon concentration compared to the prior art, and to finish the decarburization processing of the molten steel at an appropriate timing based on the estimated value of the molten steel carbon concentration obtained with high accuracy. Can do.

  By applying the present invention to the decarburization treatment of molten steel, the decarburization treatment of the molten steel can be terminated at an appropriate timing for each charge, so that excessive continuation of the decarburization treatment of the molten steel is suppressed, and the decarburization treatment of the molten steel Shortening of time can be promoted. As a result, it is possible to efficiently produce the target low carbon concentration molten steel without deviating from the standard value of the carbon concentration required for the molten steel, and it is possible to reduce the utility cost required for the decarburization treatment of the molten steel.

  In addition, in embodiment mentioned above, although the molten steel 16 which contains oxygen required for a decarburization process as dissolved oxygen was used, this invention is not limited to this. For example, an oxygen supply mechanism such as an oxygen blowing tuyere or an oxygen blowing lance is appropriately provided in the vacuum chamber 3 of the vacuum degassing apparatus 1, and oxygen necessary for decarburization treatment is blown into the molten steel 16 in the vacuum chamber 3. Thus, the molten steel 16 may be decarburized. In this case, the control unit 15 may be configured to stop the oxygen supply to the molten steel 16 by the oxygen supply mechanism of the vacuum chamber 3 at the end timing of the decarburization process of the molten steel 16.

  Moreover, in embodiment mentioned above, although the RH-type vacuum degassing apparatus 1 provided with two dip tubes was illustrated, this invention is not limited to this. That is, the present invention can also be applied to a DH vacuum degassing apparatus having a single dip tube.

  Further, in the embodiment described above, after measuring the flow rate of the exhaust gas from the vacuum chamber 3, the carbon monoxide concentration and the carbon dioxide concentration in the exhaust gas are measured, but the present invention is limited to this. It is not a thing. In the present invention, after measuring the carbon monoxide concentration and the carbon dioxide concentration in the exhaust gas from the vacuum chamber 3, the flow rate of the exhaust gas may be measured, or the carbon monoxide concentration, the carbon dioxide concentration, and the exhaust gas The flow rate may be measured simultaneously.

  In addition, the present invention is not limited by the above-described embodiment or example, and the present invention includes a configuration in which the above-described constituent elements are appropriately combined. In addition, all other embodiments, examples, operation techniques, and the like made by those skilled in the art based on the above-described embodiments are included in the present invention.

DESCRIPTION OF SYMBOLS 1 Vacuum degassing apparatus 2 Ladle 3 Vacuum tank 3a Ascending side immersion pipe 3b Decreasing side immersion pipe 3c Exhaust pipe 4 Vacuum exhaust apparatus 5 Recirculation gas supply pipe 6 Gas valve 7 Recirculation gas flow meter 8 Deoxidation material input part 9 In-tank vacuum gauge 10 Exhaust gas flow meter 11 Exhaust gas component analyzer 12 Measurement probe 13 Input unit 14 Storage unit 15 Control unit 16 Molten steel

Claims (6)

A vacuum tank that has a dip tube immersed in the molten steel in the ladle, and performs decarburization treatment of the molten steel by sucking the molten steel from the ladle through the dip tube under a reduced pressure lower than atmospheric pressure;
The flow rate of the molten steel circulating between the ladle and the vacuum tank through the dip tube during the decarburization treatment is calculated by taking into account the change in the inner diameter of the dip tube accompanying the reflux of the molten steel. And the calculated flow rate of the molten steel, the material balance equation regarding the carbon in the molten steel in the decarburization process, the decarburization rate of the molten steel, and the decarburization reaction of the molten steel in the vacuum chamber Based on the reaction model formula, a carbon concentration in the molten steel is estimated, and a controller that terminates the decarburization process at a timing when the estimated carbon concentration reaches a predetermined target value;
A vacuum degassing apparatus comprising: A temperature concentration measuring unit for measuring the temperature of the molten steel and the oxygen concentration in the molten steel;
The control unit is configured to calculate the temperature of the molten steel and the oxygen based on an estimation formula of the carbon concentration in the molten steel derived based on the mass balance equation, the decarburization rate calculation formula, and the reaction model formula in the tank. The vacuum degassing apparatus according to claim 1, wherein the carbon concentration in the molten steel is estimated using the concentration and the ring flow rate of the molten steel. An exhaust gas flow meter for measuring the flow rate of exhaust gas discharged from the vacuum chamber during the decarburization treatment;
An exhaust gas component analyzer that performs a component analysis of the exhaust gas and measures a carbon monoxide concentration and a carbon dioxide concentration in the exhaust gas;
Further comprising
The control unit calculates a decarburization rate of the molten steel using the flow rate of the exhaust gas, the carbon monoxide concentration, and the carbon dioxide concentration, and whether the calculated decarburization rate is equal to or less than a predetermined rate. The vacuum degassing apparatus according to claim 1 or 2, wherein the carbon concentration in the molten steel is estimated when the decarburization speed is equal to or less than the predetermined speed. A dip tube of a vacuum tank is immersed in the molten steel in the ladle, and the molten steel is decarburized while circulating the molten steel between the ladle and the vacuum tank through the dip tube under a reduced pressure lower than atmospheric pressure. In the decarburization processing method of the molten steel using the vacuum degassing device that performs
The flow rate of the molten steel between the ladle and the vacuum chamber is calculated by taking into account the change in the inner diameter of the dip tube accompanying the flow of the molten steel, the calculated flow rate of the molten steel, Based on the material balance equation for carbon in the molten steel in the carbon treatment, the decarburization rate of the molten steel, and the reaction model equation in the tank representing the decarburization reaction of the molten steel in the vacuum tank, A molten steel carbon concentration estimation step for estimating the carbon concentration;
A decarburization processing end step of ending the decarburization processing at a timing when the carbon concentration estimated by the molten steel carbon concentration estimation step reaches a predetermined target value;
A decarburization processing method for molten steel, comprising: A temperature concentration measuring step of measuring the temperature of the molten steel and the oxygen concentration in the molten steel,
The molten steel carbon concentration estimation step is based on the estimation formula of the carbon concentration in the molten steel derived based on the mass balance equation, the calculation formula of the decarburization rate, and the reaction model equation in the tank, and the temperature of the molten steel. The method for decarburizing molten steel according to claim 4, wherein the carbon concentration in the molten steel is estimated using the oxygen concentration and the ring flow rate of the molten steel. An exhaust gas flow rate measuring step for measuring a flow rate of exhaust gas discharged from the vacuum chamber during the decarburization treatment;
An exhaust gas component concentration measurement step of performing a component analysis of the exhaust gas and measuring a carbon monoxide concentration and a carbon dioxide concentration in the exhaust gas;
A decarburization rate calculating step of calculating a decarburization rate of the molten steel using the flow rate of the exhaust gas, the carbon monoxide concentration, and the carbon dioxide concentration;
A determination step of determining whether or not the decarburization speed calculated by the decarburization speed calculation step is a predetermined speed or less;
Further including
6. The method for decarburizing molten steel according to claim 4 or 5, wherein the molten steel carbon concentration estimating step estimates the carbon concentration in the molten steel when the decarburizing speed is equal to or lower than the predetermined speed.

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