JP2005206877A - Method for estimating carbon concentration at blowing time in converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for estimating a carbon concentration at blowing time in a converter, concretely, a carbon concentration after tapping molten steel, by which in the case of adjusting the components at the blowing in the converter, the steel tapping into a ladle and further, a secondary refining, etc., the load of this adjustment of composition can be reduced. <P>SOLUTION: When the molten steel held in the converter is tapped into the ladle by tilting into the ladle after blowing by using the converter, at the end stage of the blowing, oxygen partial pressure in slag in the converter is measured, and based on this measured value of this oxygen partial pressure and the operational condition factor at the blowing time, the carbon concentration after tapping the molten steel as the carbon concentration in the molten steel at the completing time of the molten steel tapping into the ladle, is estimated. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a method for estimating the carbon concentration at the time of converter blowing. Specifically, after performing blowing using the converter, the molten steel accommodated in the converter is discharged to the ladle. A method of accurately estimating the carbon concentration of molten steel stored in the ladle at the time of completion of steel extraction from the converter to the ladle when performing steel (referred to in this specification as `` carbon concentration after steel extraction '') About.

  In the blowing process in which oxygen, air, water vapor, or oxidizing gas such as carbon dioxide gas is blown into the hot metal contained in the converter, the steel is refined at the end of the blowing process in order to achieve high quality and low cost. It is extremely important to control the carbon concentration and temperature of the steel with high accuracy.

  Therefore, at the final stage of blowing near the end point, until the target carbon concentration is reached from the time of measurement calculated from the carbon concentration and temperature of the molten steel measured using the sublance placed inside the converter and the model formula. Dynamic control method for controlling the carbon concentration and temperature of molten steel to desired values at the end of blowing by supplying oxygen and coolant according to the amount of oxygen blown and coolant input to be supplied during Many are known.

For example, in Patent Document 1, the decarburization rate constant and the decarburized transition carbon concentration are calculated based on the operating condition factors (for example, the slag volume, the top bottom blowing gas flow rate, and the lance hot water surface distance). An invention for estimating the carbon concentration and temperature of molten steel at the end of the above is disclosed.
JP 2001-11521

  However, in the conventional invention disclosed in Patent Document 1 and the like, the amount of oxygen contained in the slag, that is, the variation in the decarburization speed due to the variation in the blowing process such as the oxygen partial pressure in the slag and the secondary combustion rate is completely eliminated. Not considered. For this reason, if an attempt is made to estimate the carbon concentration and temperature of the molten steel at the end of blowing (at the time when oxygen from the lance is blown off) according to the conventional invention, an error will inevitably occur in the estimated value.

  Moreover, in these inventions, if the post-blowing carbon concentration, which is the carbon concentration of the molten steel at the time when the steel starts from the converter to the ladle, is determined, the post-steeling carbon concentration is uniquely determined. Therefore, the decarburization reaction of the molten steel caused by oxygen in the slag is not considered at all. For this reason, even if the carbon concentration after blowing can be estimated with high accuracy, the estimation accuracy of the post-steeling carbon concentration is lowered.

  In Table 1, based on the conventional invention, the post-steeling carbon amount is less than 0.10% by mass (hereinafter, unless otherwise specified, “%” means “% by mass”) Low carbon steel, medium carbon steel with carbon content after steel output of 0.10% or more and less than 0.20%, and high carbon steel with carbon content after steel output of 0.20% or more An example of the deviation of the estimated value when estimated is shown as a percentage.

  As shown in Table 1, the deviation of the estimated value of the carbon concentration after blowing is small, about 0.004 to 0.010%, and the estimation accuracy is high for both low carbon steel, medium carbon steel and high carbon steel. However, it can be seen that the deviation in the estimated value of the post-steeling carbon concentration is significantly greater than the deviation in the estimated value of the carbon concentration after blowing and the estimation accuracy is greatly reduced.

  For this reason, after performing blowing by a converter according to the conventional invention, tilting the converter to perform steel removal to the ladle, and then trying to adjust the components such as secondary refining, the secondary The load of component adjustment in refining etc. is increased, and the cost and heat rise required for the alloy iron necessary for this component adjustment, and the decrease in quality and yield due to the increase in the carbon concentration blowing rate can be avoided. It was a big operational problem.

  The object of the present invention is to reduce the load of this component adjustment when performing component adjustment such as blowing by a converter, tapping into a ladle, and secondary refining, and this is necessary for this component adjustment. Carbon concentration at the time of converter blowing that can improve the quality and yield due to the reduction in the cost and heating amount required for the alloyed iron, and also the reduction in the carbon concentration blowing rate, specifically after steel output It is to provide a method for estimating the carbon concentration.

  The present invention relates to the slag in the converter at the end of the blowing, when the converter is tilted and then the converter is tilted to take out the molten steel contained in the converter into the ladle. At the time of converter blowing, the carbon concentration of the molten steel is estimated based on the oxygen partial pressure in the steel, for example, the post-steeling carbon concentration, which is the carbon concentration of the molten steel when the steel is drawn into the ladle It is an estimation method of carbon concentration.

  Further, the present invention provides a converter at the final stage of blowing when the converter is tilted after the converter is tilted and the molten steel contained in the converter is taken out into the ladle. Measure the oxygen partial pressure in the slag inside, and based on the measured value of this oxygen partial pressure and the operating condition factor at the time of blowing, it is the carbon concentration of the molten steel when the steel is discharged to the ladle This is a method for estimating the carbon concentration during converter blowing, characterized by estimating the carbon concentration after steelmaking. In this case, it is exemplified that the post-steeling carbon concentration is estimated using a decarburization rate constant determined by using the measured oxygen partial pressure in the slag and the operating condition factor during blowing. Is done.

  In these methods for estimating the carbon concentration at the time of converter blowing according to the present invention, the oxygen partial pressure in the slag includes a reference electrode and a reference electrode made of a solid electrolyte, and this reference electrode serves as the slag in the converter. In order to improve the estimation accuracy associated with shortening the measurement time, measurement is performed by performing calculation based on this electromotive force using a sublance that forms the electromotive force of the oxygen concentration cell by contact. desirable.

  Further, in the carbon concentration estimation methods during the converter blowing according to the present invention, the post-steeling carbon concentration takes into account the increase in carbon concentration due to the alloy iron that is introduced when steeling into the ladle. Then, the estimation is exemplified. In other words, the post-steeling carbon concentration increases due to the alloy iron introduced into the steeling. For this reason, if the post-steeling carbon concentration is estimated by adding an increase in the carbon concentration due to the alloyed iron added to the estimated carbon concentration obtained by the present invention, this estimated value is added to the ladle. The actual analytical value of the molten steel that has been steeled out can be substantially matched.

  According to the present invention, when the converter is tilted after being blown using the converter, the molten steel contained in the converter is taken out into the ladle. When the steel removal to the ladle is completed based on the partial pressure of oxygen in the slag, specifically using the decarburization rate constant determined from this partial pressure of oxygen and the operating conditions during converter blowing. Since the post-steeling carbon concentration, which is the carbon concentration of the molten steel, is estimated, the estimation accuracy of the post-steeling carbon concentration can be significantly increased.

  For this reason, quality and yield are reduced by reducing the iron alloy cost required for adjusting the components, such as secondary refining, etc., reducing the amount of heat rise, and further reducing the carbon concentration blowing rate, which is performed after steel is extracted to the ladle. Cost reduction can be achieved by improving the cost.

BEST MODE FOR CARRYING OUT THE INVENTION The best mode for carrying out the carbon concentration estimation method during converter blowing according to the present invention will be described in detail below.
First, the background and principle of the present invention will be described.

  The mechanism by which the post-steel carbon concentration varies irregularly from the carbon concentration after blowing, for example, the mechanism that the post-steel carbon concentration fluctuates from 0.40 to 0.30% for molten steel with a blown carbon concentration of 0.40%. explain.

  Not all of the oxygen blown from the lance during blowing by the converter is used up for the decarburization reaction in the converter, and some of the blown oxygen is expressed by the following formulas (1) and (2) Is accumulated in the slag in the converter by the reaction indicated by. Note that the amount of oxygen accumulated varies depending on the blowing conditions for each blowing.

Fe + O ＝ FeO ………… (1)
Mn + O ＝ MnO ………… (2)
The oxygen accumulated in the slag in this way is agitated between the slag and the molten steel, for example, by tilting the converter or discharging it from the converter before the steel output from the converter to the ladle is completed. When it becomes active, it reacts with the carbon in the molten steel by the reaction shown by the following formulas (3) and (4) to reduce the carbon content of the molten steel.

FeO + C ＝ Fe + CO ………… (3)
MnO + C ＝ MnO ………… (4)
For this reason, the post-steeling carbon concentration inevitably deviates from the post-blowing carbon concentration, and it accumulates in the slag shown by the equations (1) to (4) when estimating the post-steeling carbon concentration. If the decarburization reaction of the molten steel due to the released oxygen is not taken into account, even if the post-blowing carbon concentration can be estimated with high accuracy, the post-steeling carbon concentration estimation accuracy is unsatisfactory. Therefore, in order to improve the estimation accuracy of the carbon concentration after blowing, it is essential to use the oxygen partial pressure in the slag in the converter as an estimation factor.

  By the way, as an invention for estimating the oxygen partial pressure of slag at the time of blowing for estimating components (P, Mn) in molten steel, for example, Japanese Patent Laid-Open No. 5-239524 discloses analysis values of exhaust gas components. In which the partial pressure of oxygen in the slag is estimated from the measured value of the slag and the measured value of the slag level. Inventions for bringing the components of the molten steel closer to the target are disclosed.

  However, in these inventions, it takes time to analyze the exhaust gas components, so it is difficult to accurately estimate the partial pressure of oxygen in the slag from the time difference between when the exhaust gas components are sampled and when the analysis is completed. .

  Therefore, in the present embodiment, for example, using a sub lance that includes a reference electrode and a reference electrode made of a solid electrolyte, and forms an electromotive force of the oxygen concentration cell by contacting the reference electrode with the slag in the converter, By calculating based on this electromotive force, the partial pressure of oxygen in the slag is measured almost in real time in the short term at the end of blowing, and this partial pressure of oxygen in the slag in the converter at the end of blowing is measured. Based on the value, the post-steeling carbon concentration, which is the carbon concentration of the molten steel when steeling to the ladle is completed, is estimated. For this reason, according to this Embodiment, the estimation precision of post-steeling carbon concentration can be raised extremely.

Next, the present invention will be described in more detail with reference to the accompanying drawings.
In the method for estimating the carbon concentration at the time of converter blowing according to the present embodiment, at the time of converter blowing, oxygen accumulated in the slag by the end of the blowing is decarburization reaction thereafter, that is, sublance. Measurement of oxygen partial pressure in slag using slag-Since it greatly affects the decarburization reaction during the completion of steel extraction from the converter to the ladle, the oxygen partial pressure in slag is measured at the end of blowing, This measured value is used as an estimation factor of the post-steeling carbon concentration.

Figure 1 shows the analytical concentration (%) of T.Fe + MnO in the slag sampled at the end of blowing and when the carbon concentration and temperature of the molten steel were measured by the sublance, and the blowing after the measurement by this sublance. 6 is a graph showing an example of a relationship with decarbonation efficiency (% / Nm ³ / T) until the end of smelting. Decarbonation efficiency (% / Nm ³ / T) = (carbon concentration at the time of measurement by sublance−carbon concentration at the time of blowing;%) / (supplied oxygen amount; Nm ³ / T). In this example, the carbon concentration at the time of measurement by the sublance was 0.30%, and the carbon concentration at the time of blowing was 0.18%.

  As shown in the graph of Fig. 1, the higher the T.Fe + MnO (%) in the slag, the greater the decarbonation efficiency, and the oxygen in the slag affects the estimation accuracy of the carbon concentration at the time of blowing. It can be seen that This is because oxygen in the slag slightly contributes to the decarburization reaction at the end of blowing.

FIG. 2 is a graph showing an example of the relationship between the concentration of T.Fe + MnO in the moving bath slag collected in the same manner and the deviation ΔC (%) of the carbon concentration after blowing and the carbon concentration after steelmaking It is.
As shown in the graph of FIG. 2, the higher the T.Fe + MnO concentration in the slag and the higher the carbon concentration at the end of blowing, the deviation ΔC ( %) Increases.

  The reason for this is that during the steel output, for example, the slag and molten steel are vigorously stirred due to the tilting of the converter, the discharge from the converter, etc., so that the reaction between oxygen in the slag and carbon in the molten steel. This is because the amount increases. For this reason, as shown in Table 1 above, even if the estimation accuracy of the carbon concentration after blowing is high, the estimation accuracy of the post-steeling carbon concentration is not good.

  Therefore, grasping T.Fe and MnO in the slag at the end of the blow smelting is extremely effective in improving the estimation accuracy of the post-steel carbon concentration. However, collecting and analyzing slag during blowing requires a considerable amount of time, and thus cannot be used for dynamic control for estimating the post-steel carbon concentration. Therefore, in the present embodiment, the oxygen partial pressure in the molten steel is directly measured using a sublance described below.

  FIG. 3 is an explanatory diagram conceptually showing the sublance 1 used in the present embodiment. The sublance 1 used in the present embodiment has a probe for measuring the carbon concentration and temperature of molten steel as well as the known sublance, and is additionally provided with a reference electrode made of a solid electrolyte for measuring slag oxygen. .

That is, it has the Mo electrode 2 as the reference electrode and the ZrO ₂ electrode 3 as the reference electrode. The sublance 1 can measure the carbon concentration and temperature of the molten steel when the probe is immersed in the molten steel, and the oxygen concentration can be measured through the reference electrode 3 made of a zirconia solid electrolyte when passing through the slag layer when it is pulled up. A battery is formed. This electromotive force E is measured, and based on the electromotive force E, the oxygen partial pressure is calculated based on the following equations (5) and (6).

PO ₂ : Partial pressure of oxygen in molten steel or slag (atm)
T: Molten steel or slag temperature (K)
E: Measurement electromotive force (mV)
F: Faraday constant 23.066 (cal / mol · mV)
R: Gas constant 1.987 (cal / mol · K)
Po ₂ (ref): oxygen partial pressure of the reference electrode (Cr / Cr ₂ O ₃ ) [Elliott & Gleiser (1963)]
10 ^{(8.936-39416 / T)}

FIG. 4 is a graph showing the relationship between the measured oxygen partial pressure logPo _{2 in} the slag and the analysis value of T.Fe + MnO (%) in the slag at that time. There is a good correlation between oxygen partial pressure logPo ₂ and T.Fe + MnO (%). For this reason, the estimation accuracy of the carbon concentration after blowing and the carbon concentration after steelmaking can be improved by considering the measured value of the oxygen partial pressure logPo _{2 in} the slag.

FIG. 5 is a graph showing the relationship between the oxygen partial pressure logPo ₂ in the slag measured at the end of blowing and the carbon concentration [C] of the molten steel.
As shown in the graph of FIG. 5, since Fe, Mn, etc. in the molten steel are oxidized during blowing, a slag with an extremely high oxygen partial pressure logPo ₂ is formed, and the CO equilibrium indicated by the dotted line is greatly increased upward. It is offset. Further, the oxygen partial pressure logPo ₂ varies at the same carbon concentration [C] and varies depending on the blowing conditions and the like.

Next, the concept of model logic considering the oxygen partial pressure logPo ₂ in the slag will be described below. FIG. 6 shows the oxygen partial pressure logPo ₂ in the slag and the carbon of the molten steel, as in the graph shown in FIG. It is a graph which shows the relationship with density | concentration [C].

As shown in the graph of FIG. 6, the amount of oxygen in the slag at the end of blowing is higher than the equilibrium (see the black circles in FIG. 6) and is excessive. This excess oxygen source approaches CO equilibrium slightly by the end of blowing (see white squares), and further approaches CO equilibrium by the end of steelmaking (see white circles). Of oxygen is used. The model logic in consideration of the oxygen partial pressure logPo ₂ in the slag in the present embodiment is logic for estimating the oxygen concentration [C] in consideration of this reaction.

First, an excess oxygen amount index in the _slag is expressed as Oslag = (logPO _2SL −logPo _2eq ) × V _slag . Here, logPO _2SL indicates the oxygen partial pressure in the slag of the sublance measurement value, logPo _2eq indicates the equilibrium oxygen partial pressure in the [C] value at the time of the sublance measurement, and Vslag indicates the slag volume.

If the contribution ratio of how much excess oxygen is supplied to the decarburization reaction after the end of blowing or after completion of steelmaking is a function of the target [C], the amount of oxygen in the slag used for the decarburization reaction The oxygen index can be expressed as Oslag (DC) = a × [C] aim × Oslag. And this was taken into account in the decarburization rate constant estimation formula
K1 = Σαi x Xi + b x Oslag (DC) (estimated at the end of blowing), or
K1 = Σαi x Xi + C x Oslag (DC) (estimated when steelmaking is completed)
It was expressed by

  In the above equation, Xi represents an operating condition factor (for example, slag volume, upper bottom blowing gas flow rate, lance hot water surface distance, etc.), and symbol α is a coefficient. The symbol b indicates a coefficient used for estimating the carbon concentration [C] at the end of blowing, and the symbol C indicates a coefficient used for estimating the carbon concentration [C] at the completion of steelmaking.

  Next, the target carbon concentration is estimated from the following oxygen balance equation using the estimated decarburization rate constant K1.

In the above oxygen balance equation, C _SL indicates the dynamic bath [C] value (%), C _aim indicates the steel output target [C] value (%), and Fo ₂ is set from the dynamic bath [C]. Indicates the oxygen intensity (Nm ³ / Ton) blown up to the value, η indicates the oxygen efficiency brought in by the auxiliary material, and W _{sub, j} indicates the actual input amount of the auxiliary material j from the moving bath to the blowing ( Ton), O _{2, j} indicates the oxygen content (Nm ³ / Ton) of the auxiliary raw material j, W _ST indicates the total weight in the furnace (hot metal weight + main raw material weight) (Ton), and κ ₁ is decarburization rate constant (% / (Nm ³ / Ton)) indicates, C _B represents the critical [C] concentration (%), C _R is decarburization limit [C] concentration; indicates (% constant = 0.02) , FB _C represents the feedback correction term (previous FB calculation value), xi] represents the degree of oxygen balance equation exponential term (constant), and further, eta denotes the auxiliary materials carry oxygen efficiency (constant).
In this way, the amount of acid delivered to the target [C] after completion of steel production is determined.

The model logic in consideration of the oxygen partial pressure logPo ₂ in the slag in the present embodiment is configured as described above.
Next, transmission / reception of information such as blowing status in the present embodiment will be described.

FIG. 7 is an explanatory view schematically showing a configuration example of the converter 11 at the time of blowing for carrying out the present invention.
As shown in the figure, the converter 11 contains hot metal 12 and is blown. A main lance 13 and a sub lance 14 are provided above the converter 11. Further, a bottom blowing nozzle 15 is provided in the lower part of the converter 11, and both the main lance 13 and the bottom blowing nozzle 15 are equipped with flow meters 16 and 17, respectively. In FIG. 7, reference numeral 18 denotes a secondary raw material shooter, and reference numeral 19 denotes a weigher.

  In the converter 11, the blown state is transmitted from these instruments when measured by the sublance 14. In addition, the measurement waveform processing at the time of measurement by the sublance is performed by the waveform calculator 20, and the measured values of the carbon concentration [C] of the molten steel 12, the temperature of the molten steel 12, and the oxygen partial pressure in the slag are all processed by the process computer 21. Is input.

  In the present embodiment, since the converter 11 shown in FIG. 7 is used, after the blowing using the converter 11, the converter 11 is tilted to remove the molten steel 12 accommodated in the converter 11. It is the carbon concentration of the molten steel when the steel output to the ladle is completed based on the partial pressure of oxygen in the slag 10 in the converter 11 at the end of the blowing process when steel is output to the pan (not shown) The carbon concentration after steel can be estimated.

Using a 210-ton top-bottom blowing converter 11 configured as shown in Fig. 7, using hot metal 12 with a carbon concentration of 3.5% to 4.0%, a slag volume of 25 to 35 kg / T, and a bottom blowing gas flow rate of 0.1 to Blast furnace blowing was performed under the conditions of 0.17 Nm ³ / min / T and top blowing acid rate of 5.0 to 3.5 Nm ³ / min / T.

  Then, when measuring the carbon concentration and temperature of the molten steel 12 with the sublance 14, simultaneously measure the oxygen partial pressure in the slag 10 with the sublance 14, and consider the oxygen partial pressure in the slag 10, Inventive Examples 1 to 3 were used for estimating the carbon concentration, and Inventive Examples 4 to 6 were used for estimating the post-steeling carbon concentration.

On the other hand, what estimated the carbon concentration after blowing without considering the oxygen partial pressure in the slag was regarded as Conventional Examples 1 to 3, and what estimated the carbon concentration after steelmaking was regarded as Conventional Examples 4 to 6. .
The results are summarized in Tables 2 and 3. The estimated [C] range in Tables 2 and 3 indicates the target range of carbon at the time of steel production.

  As shown in Tables 2 and 3, it can be seen that the estimation accuracy of carbon concentration was improved in all [C] ranges.

  For this reason, according to the present embodiment, [C] suitable medium accuracy has been improved, thereby reducing the cost of alloy iron necessary for adjusting the components in secondary refining, reducing the amount of heat rise, and reducing the downflow rate of [C]. We were able to reduce costs by improving quality and yield.

Analytical concentration (%) of T.Fe + MnO in the slag collected at the end of blowing and when carbon concentration and temperature of molten steel were measured by sublance, and until the end of blowing after measurement with this sublance 2 is a graph showing an example of the relationship with decarbonation efficiency (% / Nm ³ / T). It is a graph which shows an example of the density | concentration (DELTA) C (%) of the density | concentration of T.Fe + MnO in dynamic bath slag, the carbon concentration after blowing, and the carbon concentration after steelmaking. It is explanatory drawing which shows notionally the sublance used by this Embodiment. 3 is a graph showing the relationship between the measured oxygen partial pressure logPo ₂ in slag and the analytical value of T.Fe + MnO (%) in the slag at that time. An oxygen partial pressure LogPo ₂ in the slag measured at the end of the blowing is a graph showing the relationship between the carbon concentration of the molten steel [C]. An oxygen partial pressure LogPo ₂ in the slag is a graph showing the relationship between the carbon concentration of the molten steel [C]. It is explanatory drawing which shows typically the structural example of the converter at the time of blowing for implementing this invention.

Explanation of symbols

11 Converter
12 Hot metal
13 Main lance
14 Sublance
15 Bottom blowing nozzle
16 Flow meter
17 Flow meter
18 Bye quantity shooter
19 Weighing scale
20 Waveform calculator
21 Process computer

Claims (5)

In the slag in the converter at the final stage of the blowing, when the molten steel accommodated in the converter is tilted and discharged into the ladle after performing the blowing using the converter An estimation method of carbon concentration at the time of converter blowing, characterized by estimating the carbon concentration of molten steel based on the oxygen partial pressure of the steel. In the slag in the converter at the end of the blowing, when the molten steel accommodated in the converter is tilted and discharged into the ladle after performing the blowing using the converter The measured partial pressure of oxygen, and based on the measured value of the partial pressure of oxygen and the operating condition factors during the blowing, the steel concentration is the carbon concentration of the molten steel when the steel is discharged to the ladle A method for estimating carbon concentration during converter blowing, characterized by estimating post-carbon concentration. The post-steeling carbon concentration is estimated using a decarburization rate constant determined by using the measured oxygen partial pressure in the slag and an operating condition factor during the blowing. The estimation method of the carbon concentration at the time of the converter blowing described. The oxygen partial pressure in the slag includes a reference electrode and a reference electrode made of a solid electrolyte, and uses a sub lance that forms an electromotive force of the oxygen concentration cell when the reference electrode contacts the slag in the converter. The method for estimating a carbon concentration during converter blowing according to any one of claims 1 to 3, which is measured by performing a calculation based on the electromotive force. 5. The post-steeling carbon concentration is estimated by taking into account the increase in carbon concentration due to the alloyed iron that is introduced when the steel is tapped into the ladle. The estimation method of the carbon concentration at the time of converter blowing described in 1.

Images