WO2021200496A1 - 減圧下における溶鋼の脱炭精錬方法 - Google Patents
減圧下における溶鋼の脱炭精錬方法 Download PDFInfo
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- WO2021200496A1 WO2021200496A1 PCT/JP2021/012330 JP2021012330W WO2021200496A1 WO 2021200496 A1 WO2021200496 A1 WO 2021200496A1 JP 2021012330 W JP2021012330 W JP 2021012330W WO 2021200496 A1 WO2021200496 A1 WO 2021200496A1
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/04—Removing impurities by adding a treating agent
- C21C7/068—Decarburising
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/0068—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00 by introducing material into a current of streaming metal
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/0075—Treating in a ladle furnace, e.g. up-/reheating of molten steel within the ladle
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/10—Handling in a vacuum
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
- C21C5/52—Manufacture of steel in electric furnaces
- C21C2005/5288—Measuring or sampling devices
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C2300/00—Process aspects
- C21C2300/06—Modeling of the process, e.g. for control purposes; CII
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
- C21C5/28—Manufacture of steel in the converter
- C21C5/42—Constructional features of converters
- C21C5/46—Details or accessories
- C21C5/4673—Measuring and sampling devices
Definitions
- the present invention relates to a decarburization refining method for molten steel under reduced pressure using a vacuum degassing facility.
- vacuum degassing equipment for decarburizing and refining molten steel in the pan under reduced pressure
- various types of equipment such as RH vacuum degassing equipment, DH vacuum degassing equipment, REDA vacuum degassing equipment, and VAD vacuum refining equipment.
- decarburization and refining of molten steel in a ladle under reduced pressure is also referred to as "vacuum decarburization and refining”.
- vacuum decarburization and refining With the upgrading of steel materials and the increase in demand for them, the types of steel and the target amount that require vacuum decarburization tend to increase, and by shortening the processing time, the processing capacity of vacuum degassing equipment can be improved. It is strongly desired to reduce the steel manufacturing cost by lowering the steel output temperature in the converter.
- Patent Document 1 describes the CO gas concentration and CO 2 in which the concentrations of CO gas, CO 2 gas, and O 2 gas in the exhaust gas are analyzed and the amount of air leak in the vacuum exhaust system is corrected for the analyzed values.
- a method has been proposed in which the gas concentration is obtained and the carbon content in the molten steel is estimated from the corrected CO gas concentration and the CO 2 gas concentration based on the correlation between the corrected gas concentration obtained in advance and the carbon content in the molten steel. ..
- Patent Document 2 describes a carbon analysis value of a molten steel sample collected before the start of vacuum exhaust and a measurement immediately before the start of vacuum exhaust in a method of estimating the carbon concentration during decarburization treatment based on a vacuum decarburization reaction model of molten steel.
- a method has been proposed in which the change in the pressure Pt in the vacuum chamber is read online based on the temperature T of the molten steel and the value of the oxygen potential [O] by the oxygen potential sensor, and the carbon concentration and the oxygen concentration are calculated every moment. ..
- Patent Document 2 does not consider the influence of oxygen transfer into the slag, and accurately evaluates the oxygen balance (oxygen balance) during the acid transfer decarburization treatment accompanied by FeO formation due to the oxidation of molten steel. Since it cannot be done, there is a problem that an error occurs in the calculation.
- Patent Document 3 states that the carbon content of molten steel is estimated from the composition and amount of exhaust gas from the start of treatment, and at any time when the estimated carbon content of molten steel is in the range of 100 mass ppm to 30 mass ppm.
- a method has been proposed in which the subsequent changes in carbon concentration are estimated by calculation using a decarburization model formula.
- Non-Patent Document 1 in order to accurately analyze the decarburization reaction of molten steel in a vacuum degassing furnace, three elementary processes of substance transfer in the liquid phase, substance transfer in the gas phase, and chemical reaction rate, and internal decarburization , A decarburization reaction model considering three reactions of surface decarburization and bubble decarburization is described.
- internal decarburization is a decarburization reaction due to the generation of CO gas from the inside of molten steel having a supersaturation pressure of a certain value or more
- surface decarburization is a free surface exposed to an atmosphere under reduced pressure.
- Non-Patent Document 1 only shows the concept of analyzing the decarburization reaction of molten steel under reduced pressure, and proposes a specific refining method such as determining the end of decarburization refining at an appropriate timing. is not it.
- the present invention has been made in view of the above circumstances, and an object of the present invention is to accurately estimate the carbon concentration in molten steel at an appropriate timing when decarburizing and refining molten steel using a vacuum degassing facility. It is an object of the present invention to provide a decarburization refining method for molten steel under reduced pressure, which can determine the end of decarburization refining.
- the present inventors diligently conducted experiments and studies in order to solve the above problems.
- the following three treatment methods are performed.
- This treatment method is called "acid-feeding decarburization treatment”.
- Oxygen in molten steel by exposing undeoxidized molten steel (limbed molten steel) under reduced pressure without supplying oxygen sources such as oxidizing gas and iron oxide to the molten steel.
- the first half of the vacuum decarburization refining is decarburized by the acid feeding decarburization treatment, and the second half of the vacuum decarburization refining is the decarburization refining by the rimmed decarburization treatment.
- the present invention has been enthusiastically tested and studied on the premise of vacuum decarburization refining by the method (3), which is the most commonly used treatment method.
- the amount of decarburized during the acid transfer decarburization treatment is not accurately estimated, so that the carbon concentration in the molten steel at the start of the rimmed decarburization treatment varies.
- the present inventors have completed the present invention by estimating the amount of decarburization during the acid transfer decarburization treatment more accurately and reflecting this in the determination of the end of the rimmed decarburization treatment.
- the amount of decarburized during the acid-feeding decarburization treatment is obtained from the oxygen balance during the acid-feeding decarburization treatment, and further, a decarburization reaction model is used during the rimmed decarburization treatment after the acid-feeding decarburization treatment. It was found that the carbon concentration in molten steel can be estimated accurately by calculating the carbon concentration in molten steel.
- the present invention has been made based on the above findings, and the gist thereof is as follows.
- the estimated value of the carbon concentration in the molten steel at the start of the rimmed decarburization treatment was obtained.
- the time course of the carbon concentration in the molten steel during the rimmed decarburization treatment in the heat was calculated.
- the end time of the rimmed decarburization treatment is determined based on the calculated change over time in the carbon concentration in the molten steel during the rimmed decarburization treatment.
- the amount of decarburization in the acid transfer decarburization treatment is estimated based on the balance of oxygen during the acid transfer decarburization treatment in the heat, under the reduced pressure according to the above [1] or the above [2].
- Decarburization refining method for molten steel is estimated based on the balance of oxygen during the acid transfer decarburization treatment in the heat, under the reduced pressure according to the above [1] or the above [2].
- the amount of change in oxygen in the slag before and after the acid feeding decarburization treatment is the measured value of the oxygen potential and the slag thickness of the slag before the start of the acid feeding decarburizing treatment, and the feeding.
- delta O.D. C is oxygen-flow amount of oxygen contributed to decarburization of the molten steel during decarburization (kg)
- delta O.D. O the change amount of dissolved oxygen in the molten steel during the oxygen-flow-decarburization (kg)
- S oxygen oxygen-flow variation of the oxygen in the slag during decarburization (kg)
- O Exh is that of the oxygen supplied in the oxygen-flow-decarburization, is discharged into the exhaust system as an oxygen or carbon dioxide the amount (kg)
- F O2 is the oxygen supply amount in the oxygen-flow-decarburization (kg)
- G CO2 is the amount of carbon dioxide in the exhaust gas when the oxygen-flow-decarburization (kg)
- G O2 is Okusanda'
- ⁇ C is the amount of decarburized steel in the molten steel during the acid feeding decarburization treatment (kg)
- ⁇ is the correction coefficient ( ⁇ ) of the exhaust gas flow rate.
- the reaction boundary area of the surface decarburization is included in the calculation parameter to calculate the change with time of the carbon concentration in the molten steel, and the reaction boundary area of the surface decarburization is the rimmed decarburization treatment.
- At least the CO concentration in the exhaust gas, the CO 2 concentration in the exhaust gas, the O 2 concentration in the exhaust gas, and the molten steel are used as the operation data from moment to moment for deriving the reaction boundary area of the surface decarburization in the rimmed decarburization treatment.
- a S the reaction field area of the surface decarburization (m 2)
- a NA is rising side soaked from the cross-sectional area of the lower tank Area obtained by subtracting the cross-sectional area of the tube (m 2 )
- ⁇ is the bath surface activity coefficient
- a A is the cross-sectional area of the ascending-side immersion tube (m 2 )
- ⁇ Q is the stirring power density (W / kg).
- W is the amount of molten steel (kg)
- Q is the ring flow rate of molten steel (kg / s)
- v is the discharge flow velocity of molten steel (m / s) from the descending immersion pipe
- G is the flow rate of the circulating gas (recycling gas).
- D is the inner diameter (m) of the ascending dipping tube
- P 0 is the atmospheric pressure (torr)
- P is the pressure in the vacuum chamber (torr)
- ⁇ m is the density of molten steel (kg / min).
- gamma is the proportionality constant (1 ⁇ 10 4 ⁇ 1 ⁇ 10 5)
- P CO CO gas partial pressure in the vacuum chamber atmosphere
- T is, the molten steel temperature (K)
- c co_gas is in the exhaust gas CO gas concentration (mass%)
- c co2_gas are the CO 2 gas concentration (mass%) in the exhaust gas.
- the decarburization end determination is made at an appropriate timing. Can be performed, and the vacuum decarburization refining time can be shortened.
- FIG. 1 is a schematic vertical sectional view of an example of an RH vacuum degassing device.
- the decarburization refining method for molten steel under reduced pressure is a decarburization treatment in which an oxidizing gas is sprayed on the molten steel under reduced pressure to carry out a decarburization treatment, and after the acid feeding decarburization treatment, the oxidation is performed.
- a decarburization refining method under reduced pressure including a rimmed decarburization treatment in which the supply of an oxygen source containing a sex gas to molten steel is stopped and decarburization is carried out under reduced pressure until the carbon concentration in the molten steel becomes equal to or lower than the target. Is.
- the amount of decarburization in the decarburization treatment was estimated and estimated using the operation data at the start of the decarburization treatment and the end of the decarburization treatment.
- the estimated value of the carbon concentration in the molten steel at the start of the rimmed decarburization treatment is obtained.
- the change over time in the molten steel during the rimmed decarburization treatment in the heat was calculated, and the calculated value in the molten steel during the rimmed decarburization treatment was calculated.
- the end time of the rimmed decarburization treatment is determined based on the change over time in the carbon concentration.
- Vacuum degassing equipment capable of performing the decarburization refining method for molten steel under reduced pressure includes RH vacuum degassing equipment, DH vacuum degassing equipment, REDA vacuum degassing equipment, VAD vacuum refining equipment and the like. The most typical equipment among them is the RH vacuum degassing device. Therefore, first, the vacuum degassing refining method in the RH vacuum degassing device will be described.
- FIG. 1 shows a schematic vertical sectional view of an example of an RH vacuum degassing device.
- reference numeral 1 is an RH vacuum degassing device
- 2 is a ladle
- 3 is molten steel
- 4 is a refining slag
- 5 is a vacuum tank
- 6 is an upper tank
- 7 is a lower tank
- 8 is an ascending side immersion pipe
- 9 Is a descending immersion pipe
- 10 is a recirculation gas blowing pipe
- 11 is a duct
- 12 is a raw material input port
- 13 is a top blowing lance.
- Reference numeral 14 is an oxidizing gas flow meter for measuring the flow rate of the oxidizing gas supplied from the top blown lance
- 15 is an exhaust gas flow meter for measuring the flow rate of the exhaust gas discharged from the duct
- 16 is the exhaust gas flow meter discharged from the duct.
- It is a gas analyzer that measures the concentration of the components (CO gas, CO 2 gas, O 2 gas) of the exhaust gas.
- Reference numeral 17 is a storage / arithmetic unit, which stores operation data input from the oxidizing gas flow meter 14, the exhaust gas flow meter 15, the gas analyzer 16, and the like, and uses these operation data. It is a storage / arithmetic device that calculates equations (1) to (24), which will be described later. Further, D L is ladle average inner diameter, D S is the outer diameter of the raised side dip tube and descending side dip tube, d s is the slag thickness.
- the vacuum tank 5 is composed of an upper tank 6 and a lower tank 7, and the top blowing lance 13 is a device for spraying an oxidizing gas or a medium solvent onto the molten steel in the vacuum tank to add the vacuum tank 5. It is installed on the upper part and can move up and down inside the vacuum chamber 5.
- the ladle 2 containing the molten steel 3 is raised by an elevating device (not shown), and the ascending-side immersion pipe 8 and the descending-side immersion pipe 9 are immersed in the molten steel 3 in the pan. .. Then, the inside of the vacuum tank 5 is exhausted by an exhaust device (not shown) connected to the duct 11, the inside of the vacuum tank 5 is depressurized, and the inside of the rising side immersion pipe 8 from the recirculation gas blowing pipe 10 is used. Inject gas for circulation into the air.
- the molten steel 3 in the ladle rises in proportion to the difference between the atmospheric pressure and the pressure (vacuum degree) in the vacuum chamber, and flows into the vacuum chamber. Further, the molten steel 3 in the ladle rises along with the recirculation gas and flows into the inside of the vacuum chamber 5 by the gas lift effect of the recirculation gas blown from the recirculation gas blowing pipe 10. The molten steel 3 that has flowed into the inside of the vacuum chamber 5 due to the pressure difference and the gas lift effect returns to the ladle 2 via the lowering side immersion pipe 9.
- the flow of molten steel that flows from the ladle 2 into the vacuum tank 5 and returns from the vacuum tank 5 to the ladle 2 is called "circulation".
- the molten steel 3 forms a recirculation, and the molten steel 3 is subjected to RH vacuum degassing refining. NS.
- the molten steel 3 is exposed to the atmosphere under reduced pressure in the vacuum chamber, and hydrogen and nitrogen in the molten steel move from the molten steel 3 into the atmosphere in the vacuum chamber, and the molten steel 3 is dehydrogenated and denitrified. Will be done.
- the molten steel 3 is in an undeoxidized state, it is exposed to an atmosphere under reduced pressure, so that carbon in the molten steel reacts with dissolved oxygen in the molten steel to generate CO gas, and this CO gas is used in a vacuum chamber. It moves into the atmosphere inside, and the decarburization reaction of the molten steel 3 proceeds. This decarburization reaction corresponds to the rimmed decarburization treatment.
- an oxidizing gas is sprayed from the top-blown lance 13 onto the undeoxidized molten steel 3 in the vacuum chamber to send acid.
- Carry out decarburization The carbon in the molten steel reacts with oxygen in the oxidizing gas supplied from the top-blown lance 13 to become CO gas, and this CO gas moves into the atmosphere in the vacuum chamber, and the decarburization reaction of the molten steel 3 proceeds. do.
- oxygen gas industrial pure oxygen gas
- a mixed gas of oxygen gas and an inert gas, oxygen-enriched air, or the like is used as the oxidizing gas to be blown from the top blowing lance 13.
- the dissolved oxygen concentration in the molten steel increases due to the oxidizing gas blown from the top-blown lance 13.
- the supply of an oxygen source such as iron oxide to the molten steel 3, including the supply of the oxidizing gas from the top-blown lance 13, is stopped, and the process shifts to the rimmed decarburization treatment under reduced pressure.
- the rimmed decarburization treatment the rimmed decarburization treatment is continued until the carbon concentration in the molten steel becomes lower than the target, and after the time when the carbon concentration in the molten steel becomes lower than the target, the deoxidizing material such as metallic aluminum is transferred to the molten steel 3. Addition to complete the rimmed decarburization process.
- the addition of a deoxidizing material such as metallic aluminum reduces the dissolved oxygen in the molten steel and completes the rimmed deoxidizing treatment.
- the present inventors are in the initial stage of vacuum decarburization refining. It was examined to accurately obtain the oxygen balance during the acid feeding and decarburization treatment period. As a result, as the operation data for obtaining the oxygen balance, not only the dissolved oxygen in the molten steel and the oxygen in the oxidizing gas used for the decarburization reaction, but also the oxygen contained in the slag 4 such as FeO and MnO is taken into consideration. We found that the amount of decarburized was calculated based on the balance. It was found that the carbon concentration in the molten steel after the acid transfer decarburization treatment can be estimated accurately by determining the oxygen balance by this method.
- the estimation of the decarburization amount using the carbon balance in the exhaust gas is not applicable to the determination of the end of decarburization because the accuracy is insufficient in the extremely low coal region where the carbon concentration in the molten steel is 50 mass ppm or less.
- the decarburization reaction model in estimating the carbon concentration in the molten steel during the rimmed decarburization treatment including the extremely low coal region.
- the consumption breakdown of the blown oxygen for each treatment (decarburization reaction, secondary combustion, slag oxidation). , Exhaust), which causes a problem that the estimation accuracy drops.
- the breakdown of the consumption of blown oxygen including the amount of oxygen consumed for decarburization during the acid transfer decarburization process can be accurately evaluated. It is possible to do.
- the end time of the acid transfer decarburization treatment is clearly defined by utilizing the transition of the oxygen concentration in the exhaust gas, and the actual measurement timing of the oxygen amount in the slag and the decarburization reaction model are used at that time. Match the timing of switching to carbon concentration estimation. This makes it possible to eliminate the influence of variations in the consumption breakdown of blown oxygen and reduce the estimation error.
- the oxygen balance during acid decarburization treatment is expressed by the following equations (1) and (2).
- delta O.D. C is oxygen-flow amount of oxygen contributed to decarburization of the molten steel during decarburization (kg)
- delta O.D. O the change amount of dissolved oxygen in the molten steel during the oxygen-flow-decarburization (kg)
- S oxygen oxygen-flow variation of the oxygen in the slag during decarburization (kg)
- O Exh is that of the oxygen supplied in the oxygen-flow-decarburization, is discharged into the exhaust system as an oxygen or carbon dioxide the amount (kg)
- F O2 is the oxygen supply amount in the oxygen-flow-decarburization (kg)
- G CO2 is the amount of carbon dioxide in the exhaust gas when the oxygen-flow-decarburization (kg)
- G O2 is Okusanda'
- ⁇ C is the amount of decarburized steel in the molten steel during the acid feeding decarburization treatment (kg)
- ⁇ is the correction coefficient ( ⁇ ) of the exhaust gas flow rate.
- the correction coefficient ( ⁇ ) is determined based on past results so that the left side and the right side of equation (1) are equal.
- the test heat for determining the ⁇ value is performed a plurality of times, and in each test heat, the ⁇ value is calculated so that the left side and the right side of the equation (1) are equal to each other, and the calculated test heat of each test heat is calculated.
- the ⁇ value can be arithmetically averaged to determine the ⁇ value used in the operation.
- the test heat for determining the ⁇ value is preferably at least 5 heats.
- ⁇ that minimizes the error between the calculated molten steel carbon concentration and the actual molten steel carbon concentration in the last few heats (5 to 50 heats) may be calculated and obtained each time.
- the ⁇ value thus obtained is about 0.2 to 2.0 according to the tests of the present inventors, but is not limited to this value and may be appropriately determined.
- delta O.D. O and delta O.D. S are both values after oxygen-flow decarburization previous value from the oxygen-flow decarburizing processing is defined to be a positive value when the increase.
- the first term on the right side represents the amount of oxygen used for the oxidation of CO gas by the secondary combustion. This is because CO gas is generated in the decarburization reaction and CO 2 gas is not generated, so that the CO 2 gas in the exhaust gas is generated by the secondary combustion of the CO gas.
- the oxygen input amount in the equation (1) is from the top blown lance in the acid transfer decarburization process. It is the amount of oxygen gas contained in the supplied oxidizing gas. Also, output the amount of oxygen, and the oxygen amount delta O.D. C that contributed to decarburization of the molten steel, the amount of change delta O.D. O dissolved oxygen in the molten steel, the amount of change delta O.D. S of the oxygen in the slag, in the exhaust system as an oxygen or carbon dioxide It can be considered to be the sum of the amount of oxygen discharged and OExh. In this case, the change amount delta O.D. O and variation delta O.D. S will increase.
- Variation delta O.D. O of dissolved oxygen before and after the oxygen-flow decarburization the oxygen potential of the ladle molten steel, obtained by measuring using a Hakasan probe.
- Variation delta O.D. S of the oxygen in the slag, the oxygen concentration c 0_1 (mass%) of the previous slag oxygen-flow, slug thickness d s_1 (m) of the previous oxygen-flow, oxygen concentration c in the slag after oxygen-flow 0_2 ( (Mass%) and slag thickness d s_2 (m) after acid feeding are obtained, and are obtained from the following equation (11).
- c 0_1 the oxygen concentration in the pre-oxygen-flow slag (wt%)
- c 0_2 the oxygen concentration c 0_2 in the slag after oxygen-flow (mass%)
- d s_1 is oxygen-flow before slag thickness (m)
- d s_2 the slag thickness after oxygen-flow (m)
- D L is ladle average inner diameter ((upper end diameter + bottom diameter) / 2, units; m)
- D s is the immersion tube
- the outer diameter (m) and ⁇ s are the slag density (kg / m 3 ).
- Oxygen concentration c 0_2 of oxygen concentration c 0_1 and slag in the slag is defined by the following equation (12).
- c 0_1 , 2 means that the oxygen concentration in the slag is c 0_1 or the oxygen concentration in the slag is c 0_2.
- X i is the concentration (mass%) of the slag component i produced during the acid feeding decarburization treatment period in the slag
- mi and all are the molecular weights of the slag component i
- mi and O are the slag components. It is the total atomic weight of oxygen in the molecular weight of component i.
- the component i refers to a component of the metal oxide in the slag that is produced during the acid transfer decarburization treatment period. Specifically, FeO, Fe 2 O 3 , MnO, Al 2 O 3 , SiO 2 , and TiO 2 And so on.
- the metal oxide mainly generated during the acid transfer decarburization treatment period is FeO, and therefore the component i needs to contain FeO. Since the amount of change (increase) of oxides other than FeO is smaller than that of FeO, there is no problem even if they are not included in component i, but it is desirable to include them.
- the slag thickness d s_1 and the slag thickness d s_2 may be obtained by immersing a metal rod in molten steel and physically measuring the height (thickness) of the slag layer adhering to the metal rod. It may be measured using a vortex sensor.
- the oxygen concentration in the slag may be determined by directly measuring the oxygen potential of the refined slag with a solid electrolyte sensor, or by collecting a slag sample and analyzing the slag sample.
- the component i as FeO and MnO determine the FeO concentration and MnO concentration in the slag, to calculate the oxygen concentration c 0_2 of oxygen concentration c 0_1 and slag using equation (12). If determined by the analysis carried out composition analysis of slag samples, from the analysis results, we obtain the X i for each oxide, calculates the oxygen concentration c 0_2 of oxygen concentration c 0_1 and slag by equation (12).
- the amount of oxygen discharged to the exhaust system OExh is a flow rate obtained by measuring the exhaust gas flow rate, the CO 2 gas concentration in the exhaust gas, and the O 2 gas concentration in the exhaust gas with the exhaust gas flow meter 15 and the gas analyzer 16, respectively.
- the amount of oxygen is derived from the product of and the concentration.
- the exhaust gas flow rate measured by the exhaust gas flow meter 15 causes an error due to the state of the device due to leaks or the like, so the correction is determined from the actual mass balance of carbon and oxygen in the exhaust gas in the latest heat. Multiply the coefficient ⁇ .
- Oxygen supply F O2 is the measured flow rate value by the oxidizing gas flow meter 14, is calculated by the product of the oxygen purity of the oxidizing gas.
- Delta O.D. O was determined by the method described above, by substituting the delta O.D. S, O Exh, the F O2 (1) wherein the oxygen-flow-decarburization amount of oxygen delta O.D. C used for decarburization during is determined.
- Q G is the exhaust gas flow rate (kg / sec)
- co_gas is the oxygen concentration in the exhaust gas (mass%)
- co_base is the oxygen concentration in the exhaust gas (mass%) at the time when acid transfer is not performed.
- t s is the oxygen-flow-decarburization process start time
- t e is the oxygen-flow-decarburization end time.
- the time when (co_gas / co_base) fell below 1.05 after the end of acid feeding It is defined as a t e.
- ⁇ C during the acid transfer decarburization treatment can be calculated by the following equation (3).
- ⁇ C is the decarburization amount (kg) of the molten steel at the time of acid feeding decarburization treatment.
- oxygen amount delta O.D. C was the sum of the change amount delta O.D. O dissolved oxygen in the molten steel, the amount of change delta O.D. S of the oxygen in the slag, and exhaust oxygen quantity O Exh the exhaust system as an oxygen or carbon dioxide.
- the decarburization amount ⁇ C of the molten steel can also be obtained by a simple method.
- the amount of oxygen output in the acid feed decarburization treatment is at least the amount of change in oxygen in the molten steel before and after the acid feed decarburization treatment.
- delta O.D. O it is important that the sum of the variation delta O.D. S of slag in oxygen before and after the oxygen-flow-decarburization.
- the start time of the rimmed decarburization treatment is defined as the end time of the acid feeding decarburization treatment
- the end time of the rimmed decarburization treatment is defined as the addition time of the deoxidizing material.
- the decarburization reaction model formula is not limited to the formulas shown in the formulas (14) to (17), and another model formula may be used.
- [C] is the carbon concentration (mass%) of the molten steel in the pan
- [C] E is the equilibrium carbon concentration (mass%) of the molten steel in the vacuum chamber
- K is the decarburization reaction rate constant (1 /).
- s) and t are the elapsed time (s) from the end of the acid feeding decarburization treatment
- [O] is the oxygen concentration (mass%) of the molten steel in the pan
- [O]' is the pan one step before.
- the decarburization rate constant (K) can be a value determined in advance from the past processing results of similar steel grades, but as will be described later, it is calculated by including the reaction boundary area of surface decarburization, which is updated as appropriate, in the calculation parameters. It is preferable to do so. By calculating using the reaction boundary area of this surface decarburization, it is possible to estimate the carbon concentration in the molten steel during the rimmed decarburization treatment more accurately. The method will be described below.
- Non-Patent Document 1 decarburization reactions are roughly classified into three types: internal decarburization, surface decarburization, and bubble decarburization, and the decarburization rate constant (K) is represented by the following equation (18). ..
- K is the decarburization rate constant (1 / s)
- ak I is the reaction capacity coefficient of internal decarburization (m 3 / s)
- A is the cross-sectional area of the lower tank (m 2 )
- ak S is.
- AS is surface decarburization reaction boundary area (m 2 )
- ak B is bubble decarburization reaction capacity coefficient (m 3 / s)
- a B is the reaction boundary area (m 2 ) of bubble decarburization
- W is the amount of molten steel (kg)
- ⁇ m is the molten steel density (kg / m 3 ).
- the internal decarburization reaction capacity coefficient (ak I ) and the bubble decarburization reaction capacity coefficient (ak B ) are represented by the following equations (19) to (23).
- A is the cross-sectional area (m 2 ) of the lower tank
- T is the molten steel temperature (K)
- [C] is in the molten steel.
- NL / min which is a unit of the flow rate G of the recirculation gas, means the volume of the gas supplied per unit time in the standard state, and "N" is a symbol indicating the standard state. Further, in the present invention, the standard state is 0 ° C. and 1 atm.
- a S is the surface decarburization interfacial area of (m 2)
- the [pi surface reaction rate factor , ⁇ is a constant (3 to 15)
- ANA is the area obtained by subtracting the cross-sectional area of the ascending-side immersion tube from the cross-sectional area of the lower tank (m 2 )
- ⁇ is the bath surface activity coefficient
- the cross-sectional area (m 2 ) of the side immersion tube ⁇ Q is the stirring power density (W / kg), W is the amount of molten steel (kg), Q is the ring flow rate of the molten steel (kg / s), and v is the decrease.
- the discharge flow rate of molten steel from the side immersion tube (m / s) G is the flow rate of the recirculation gas (NL / min), D is the inner diameter of the ascending side immersion tube (m), and P 0 is the atmospheric pressure (torr).
- P is the pressure in the vacuum chamber (torr)
- ⁇ m is the molten steel density (kg / m 3)
- ⁇ is a proportionality constant (1 ⁇ 10 4 ⁇ 1 ⁇ 10 5)
- the P CO vacuum
- T is the molten steel temperature (K)
- c co_gas is the concentration of CO gas in the exhaust gas (mass%)
- c co2_gas is the concentration of CO 2 gas in the exhaust gas (mass%).
- the bath surface activity coefficient ( ⁇ ) in the equation (5) is treated as a fixed value as a fitting parameter in Non-Patent Document 1, but as a result of various studies, the present inventors have conducted (9). As shown in the equation, by deriving the bath surface activity coefficient ( ⁇ ) using the CO gas partial pressure ( PCO ) and the molten steel temperature (T), the estimation accuracy of the carbon concentration in the molten steel can be further improved. I found that.
- the reaction capacity coefficient (ak I ) for internal decarburization, the reaction capacity coefficient (ak S ) for surface decarburization, and the reaction capacity coefficient (ak B ) for bubble decarburization obtained as described above are shown in (18).
- the decarburization rate constant (K) can be obtained.
- the decarburization rate constant (K) is updated at predetermined intervals during the treatment in accordance with the above-mentioned update of the value of the bath surface activity coefficient ( ⁇ ).
- the carbon concentration in the molten steel during the rimmed decarburization treatment is estimated, and the end time of the rimmed decarburization treatment is determined based on the time-dependent change in the carbon concentration in the molten steel during the rimmed decarburization treatment. Specifically, after the calculated value, that is, the estimated value of the change over time in the carbon concentration in the molten steel during the rimmed decarburization treatment becomes equal to or less than the target value, a deoxidizing material such as metallic aluminum is added to the molten steel 3 to remove the rim. Finish the charcoal treatment, that is, vacuum decarburization refining.
- the present invention when decarburizing and refining molten steel using a vacuum degassing facility, it is possible to accurately estimate the carbon concentration in the molten steel, and further, decarburize at an appropriate timing. It is possible to determine the end, and the vacuum decarburization refining time can be shortened.
- the steel grade to be decarburized and refined was an extremely low coal grade with a carbon content standard upper limit of 25 mass ppm.
- oxygen gas is first blown onto the molten steel from the top-blown lance to perform acid-feeding decarburization, and then oxygen gas from the top-blown lance is included to the molten steel of an oxygen source such as iron oxide.
- the rimmed decarburization treatment was carried out by stopping the supply of carbon dioxide and carrying out the decarburization treatment under reduced pressure.
- the chemical composition of the molten steel used in the test was carbon; 0.01 to 0.06% by mass, silicon; 0.015 to 0.025% by mass, manganese; 0.1. It was ⁇ 0.3% by mass, phosphorus; 0.02% by mass or less, sulfur; 0.003% by mass or less, and the molten steel temperature before vacuum degassing refining was 1600 to 1650 ° C.
- the ultimate vacuum degree in the vacuum chamber was 0.5 to 1.0 torr (0.067 to 0.133 kPa), argon gas was used as the recirculation gas, and the flow rate of the argon gas was 2000 to 2200 NL / min.
- slag thickness d s was using measurements by direct measurement using steel bars immersion.
- the amount of oxygen in the slag is a measured value obtained by directly measuring the FeO concentration and MnO concentration in the slag using a solid electrolyte sensor, and in Example 2 of the present invention and Example 3 of the present invention, the slag is used.
- the mass concentrations of FeO, MnO, Al 2 O 3 , SiO 2 , and TiO 2 in the slag were determined by fluorescent X-ray analysis. However, the oxide mass was converted from the value of the mass in the slag of each metal element obtained from the fluorescent X-ray analysis value, assuming that the form of the oxide is one type for each metal element.
- Example 2 of the present invention the average value of the past actual results is used in Example 2 of the present invention, and (4) in Example 3 of the present invention.
- the reaction rate constants (ak I , ak S , ak B ) obtained from Eqs. (10) and (19) to (24) were substituted into Eq. (18) and the values obtained were used.
- the input parameters that fluctuate during operation are every 2 seconds using the operation data transmitted to the storage / arithmetic unit at any time.
- Updated to. (4) is a constant ⁇ of the 0.65 past operation record, the ⁇ constant of proportionality (9), and from past operations experience and 4.5 ⁇ 10 5.
- Examples 1, 2, 3 and Comparative Examples of the present invention are treated by setting the target carbon concentration to 20 mass ppm, adding metallic aluminum to the molten steel when the estimated carbon concentration falls below the target carbon concentration, and terminating the vacuum decarburization refining. 100 heats were performed in 1 and 2 respectively.
- a molten steel sample was taken from the pan, and the difference between the actual ⁇ C and the estimated ⁇ C after vacuum degassing refining obtained from the analytical values of the molten steel sample was A; Estimate by 3; B; estimation by carbon mass balance in exhaust gas (Comparative Example 1), C; estimation by decarburization estimation model of Eqs. (14) to (17) (Comparative Example 2), respectively, and ⁇ C estimation error
- the standard deviation ⁇ of each was calculated. Table 1 shows the standard deviation ⁇ obtained.
- Example 1 of the present invention The standard deviation was smaller in Examples 1, 2 and 3 of the present invention than in Comparative Examples 1 and 2, and it was confirmed that the ⁇ C estimation accuracy was improved. Further, the estimation accuracy of Examples 2 and 3 of the present invention in consideration of not only FeO and MnO contained in the slag but also oxygen contained in Al 2 O 3 , SiO 2 and TiO 2 is higher than that of Example 1 of the present invention. It was high.
- Example 2 of the present invention the decarburization rate is compared with that of Example 2 of the present invention in which the average value of the past actual results is used for the decarburization rate constant (K) used for estimating the decarburization during the rimmed decarburization treatment.
- K decarburization rate constant
Abstract
Description
前記送酸脱炭処理の後、前記酸化性ガスを含む酸素源の溶鋼への供給を停止し、目標とする溶鋼中炭素濃度以下となるまで減圧下で脱炭処理を実施するリムド脱炭処理と、
を含む減圧下における溶鋼の脱炭精錬方法であって、
脱炭精錬対象のヒートにおいて、前記送酸脱炭処理の開始時及び前記送酸脱炭処理の終了時の操業データを用いて、前記送酸脱炭処理での脱炭量を推定し、
推定した前記送酸脱炭処理での脱炭量に基づいて、前記リムド脱炭処理の開始時での溶鋼中炭素濃度の推定値を求め、
求めた前記推定値をリムド脱炭処理開始時の溶鋼中炭素濃度として、当該ヒートにおけるリムド脱炭処理中の溶鋼中炭素濃度の経時変化を計算し、
前記計算されたリムド脱炭処理中の溶鋼中炭素濃度の経時変化に基づいて前記リムド脱炭処理の終了時期を判定する、
減圧下における溶鋼の脱炭精錬方法。
2 取鍋
3 溶鋼
4 スラグ
5 真空槽
6 上部槽
7 下部槽
8 上昇側浸漬管
9 下降側浸漬管
10 環流用ガス吹き込み管
11 ダクト
12 原料投入口
13 上吹きランス
14 酸化性ガス流量計
15 排気ガス流量計
16 ガス分析計
17 記憶・演算装置
Claims (10)
- 減圧下で溶鋼に酸化性ガスを吹き付けて脱炭処理を実施する送酸脱炭処理と、
前記送酸脱炭処理の後、前記酸化性ガスを含む酸素源の溶鋼への供給を停止し、目標とする溶鋼中炭素濃度以下となるまで減圧下で脱炭処理を実施するリムド脱炭処理と、
を含む減圧下における溶鋼の脱炭精錬方法であって、
脱炭精錬対象のヒートにおいて、前記送酸脱炭処理の開始時及び前記送酸脱炭処理の終了時の操業データを用いて、前記送酸脱炭処理での脱炭量を推定し、
推定した前記送酸脱炭処理での脱炭量に基づいて、前記リムド脱炭処理の開始時での溶鋼中炭素濃度の推定値を求め、
求めた前記推定値をリムド脱炭処理開始時の溶鋼中炭素濃度として、当該ヒートにおけるリムド脱炭処理中の溶鋼中炭素濃度の経時変化を計算し、
前記計算されたリムド脱炭処理中の溶鋼中炭素濃度の経時変化に基づいて前記リムド脱炭処理の終了時期を判定する、
減圧下における溶鋼の脱炭精錬方法。 - 前記リムド脱炭処理中の溶鋼中炭素濃度の経時変化の計算値が、目標とする溶鋼中炭素濃度以下となった後に、リムド脱炭処理を終了する、請求項1に記載の減圧下における溶鋼の脱炭精錬方法。
- 前記送酸脱炭処理での脱炭量を、当該ヒートにおける送酸脱炭処理中の酸素の収支に基づいて推定する、請求項1または請求項2に記載の減圧下における溶鋼の脱炭精錬方法。
- 前記送酸脱炭処理での酸素の収支において、少なくとも、当該ヒートにおいて送酸脱炭処理中に供給された前記酸化性ガスに含まれる酸素ガスの供給量、前記送酸脱炭処理の前後での溶鋼中酸素の変化量、前記送酸脱炭処理の前後でのスラグ中酸素の変化量を、入酸素量または出酸素量として含み、前記送酸脱炭処理での脱炭量を、前記入酸素量と前記出酸素量との差から求める、請求項1から請求項3のいずれか1項に記載の減圧下における溶鋼の脱炭精錬方法。
- 前記送酸脱炭処理の前後でのスラグ中酸素の変化量を、前記送酸脱炭処理の開始前でのスラグの酸素ポテンシャルの測定値及びスラグ厚みの測定値、並びに、前記送酸脱炭処理の終了後でのスラグの酸素ポテンシャルの測定値及びスラグ厚みの測定値、から求める、請求項4に記載の減圧下における溶鋼の脱炭精錬方法。
- 前記送酸脱炭処理での脱炭量を、下記の(1)式から下記の(3)式を用いて推定する、請求項1から請求項5のいずれか1項に記載の減圧下における溶鋼の脱炭精錬方法。
- 前記リムド脱炭処理において、少なくとも表面脱炭の反応界面積を計算パラメータに含めて溶鋼中炭素濃度の経時変化の計算を行い、前記表面脱炭の反応界面積を、リムド脱炭処理中における時々刻々の操業データを用いて導出し、且つ、更新する、請求項1から請求項6のいずれか1項に記載の減圧下における溶鋼の脱炭精錬方法。
- 前記リムド脱炭処理における表面脱炭の反応界面積を導出するための時々刻々の操業データとして、少なくとも排ガス中のCO濃度を用いる、請求項7に記載の減圧下における溶鋼の脱炭精錬方法。
- 前記リムド脱炭処理における表面脱炭の反応界面積を導出するための時々刻々の操業データとして、少なくとも排ガス中のCO濃度、排ガス中のCO2濃度、排ガス中のO2濃度及び溶鋼温度を用いる、請求項7に記載の減圧下における溶鋼の脱炭精錬方法。
- 前記リムド脱炭処理における表面脱炭の反応界面積を、下記の(4)式から下記の(10)式を用いて導出する、請求項9に記載の減圧下における溶鋼の脱炭精錬方法。
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