JPH0257666B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for estimating the composition of molten steel at the end of blowing in converter steelmaking. As is well known, in the steelmaking process, it is extremely important to match the components of tapped steel, especially the contents of C, Mn, P, etc. in the tapped steel, to the target component values. In furnace steelmaking,
At the end of blowing, the furnace body is tilted to sample the molten steel, and chemical analysis is performed. If the component values of the analysis results approximately match the target values, the steel is tapped as is, and if it deviates from the target values, the steel is re-blown. After refining, etc., the steel is tapped. However, in this conventional method, sampling and analysis take a long time, and it takes an average of about 3 minutes from the end of blowing to sampling and analysis to tapping the steel. There was a problem in which the refractories of the converter were severely eroded by the stagnant molten steel. This invention was made in view of the above circumstances, and the molten steel composition at the end of blowing, especially C, without sampling and analysis at the end of blowing.
By accurately estimating the amount of Mn and P in a short period of time, the time required from the end of blowing to the time of steel tapping can be shortened, and the amount of corrosion of the refractories in the converter during that time can be reduced. The purpose is to eliminate the labor required for conventional sampling. As a result of various experiments and studies to achieve the above-mentioned purpose, the present inventors have determined the oxygen potential in molten steel at the end of blowing, the carbon concentration in molten steel, the amount of iron in slag, and the P ratio between slag and molten steel. Distribution ratio L _P , Mn distribution ratio
Since there is a correlation with L _Mo , they discovered that it is possible to estimate the amounts of C, Mn, and P in molten steel simply by measuring the oxygen potential, leading to this invention. Therefore, this invention is a method for estimating the molten steel composition after the completion of blowing when refining molten steel by oxygen blowing using a converter. The oxygen potential is measured, and the C concentration in the molten steel is estimated based on the correlation between the oxygen potential determined in advance and the C concentration in the molten steel.The Mn and P concentrations in the molten steel are estimated based on the previously determined C concentration. The Mn distribution ratio or P distribution ratio is estimated based on the correlation between the oxygen potential and the Mn distribution ratio or P distribution ratio between slag and molten steel, and then the estimated Mn distribution ratio or P distribution ratio and the charged raw material are This method is characterized in that the Mn and P concentrations are calculated by calculating the amount of Mn or P contained therein and the molten steel weight and slag weight estimated from the charged raw materials. The method of this invention will be explained in more detail below. First , we will explain the relationship between the carbon concentration in molten steel C _f at the end of blowing (at the end of blowing) and the oxygen potential O in molten steel at the end of blowing. A correlation exists. Therefore, using this correlation, the carbon concentration in molten steel C _f can be calculated directly from the oxygen potential O in molten steel.
can be estimated. On the other hand, the phosphorus concentration P _f and manganese concentration Mn _f in the molten steel at the end of blowing are calculated from the oxygen potential O in the molten steel at the end of blowing, and the phosphorus distribution ratio L _P between slag and molten steel at the end of blowing and the manganese distribution. ratio L _Mo , weight of molten steel at the end of blowing W _steel and weight of slag W _slag , total amount of P charged in the converter W _P-io and also Mn
can be estimated via the total amount W _Mo-io . In other words, hot metal, cold pig iron, scrap, and auxiliary raw materials are charged into the converter, but the total P content W _P-io of P-containing compounds in the charging material and the Mn-containing compound content in the charging material are Total Mn amount W _Mo-io , molten steel weight W _steel and slag weight W _slag at the end of blowing, P concentration in slag P _slag and Mn concentration at the end of blowing
Mn _slag and P concentration P _f in molten steel at the end of blowing
and the Mn concentration Mn _f , the following equations (1) and (2) hold from the balance of P and Mn in converter refining. P _f = (W _P-io −W _slag・P _slag )/W _steel ……(1) Mn _f = (W _Mo-io −W _slag・Mn _slag )/W _steel ……(2) Blowing here The phosphorus distribution ratio L _P and the manganese distribution ratio L _Mo at the end point can be expressed by the following (3) and (4). L _P =P _slag /P _f ...(3) L _Mo =Mn _slag /Mn _f ...(4) Therefore, equations (1) and (2) are equivalent to the following equations (5) and (6). It is shown as follows. P _f = W _P-io / (W _steel +L _P・W _slag ) ……(5) Mn _f = W _Mo-io / (W _steel +L _Mo・W _slag )……(6) (5), (6 ), the phosphorus distribution ratio L _P and the manganese distribution ratio L _Mo at the end of blowing are, for example, the second
As shown in Fig. 3, there is a good correlation with the oxygen potential O in molten steel at the end of blowing, and therefore, using this correlation, it can be estimated from the oxygen potential O and other operating factors. . On the other hand, the weight of molten steel W _steel at the end of blowing can be easily estimated from the weight of iron sources charged into the converter, such as the weight of hot metal, the weight of cold pig iron, the weight of scrap, and the weight of mill scale and iron ore. In addition, the slag weight W _slag at the end of blowing is determined by the amount of quicklime, quick dolomite, fluorspar, light calcined dolomite, iron ore, mill scale, and Si in the hot metal and cold pig iron inserted into the converter.
It is determined by the weight of the compounds produced when P, Mn, Ti, and Al are oxidized, and the weight T _Fe of the compounds mainly composed of FeO produced when molten steel is oxidized. The weight of compounds other than FeO-based compounds can be easily estimated from the charged raw materials; on the other hand, the production amount of FeO-based compounds T _Fe
For example, as shown in FIG. 4, since it corresponds well to the oxygen potential O in molten steel, it can be easily estimated using this correlation. After all, in equations (5) and (6), the phosphorus distribution ratio L _P and the manganese distribution ratio L _Mo and the slag weight W FeO in _{the slag}
The amount of compounds produced, mainly T _Fe , can be estimated from the correlation with the oxygen potential O in molten steel, and everything else can be estimated from the raw material charged in the converter, so even if the data on the raw material charged in the converter is known, For example, by measuring the oxygen potential in molten steel at the end of blowing, it is possible to estimate the C concentration, P concentration, and Mn concentration in molten steel at the end of blowing using the above-mentioned correlation. . Therefore, in the method of this invention, the correlation between the oxygen potential in molten steel and the amounts of C, Mn, and P in molten steel is determined in advance, and at the end of blowing, an oxygen concentration battery using a solid electrolyte is used to measure the oxygen concentration in molten steel. Measure the potential, and use a computer or the like to determine the C, P, and
Estimate (calculate) Mn concentration in a short time. As described above, in the method of the present invention, the oxygen potential in molten steel is measured using an oxygen concentration cell using a solid electrolyte. The reason why an oxygen concentration battery using a solid electrolyte is used is that it allows measurement at high temperatures and is easy to handle. FIG. 5 shows an example of an oxygen detection probe 1 incorporating the oxygen concentration battery. In FIG. 5, for example, ZrO ₂ is used as the solid electrolyte 2 for oxygen ion conduction.
is used, and as the standard electrode 3 in contact with the solid electrolyte 2, for example, a Cr-Cr ₂ O ₃ mixed powder is used,
Furthermore, a Mo rod _, for example, is used as the molten steel contact electrode 4, and is configured to extract the electromotive force between Mo and Cr- _Cr2O3 (oxygen concentration electromotive force E).
At the same time, the temperature T of the molten steel is measured by a thermocouple 5 made of, for example, Pr-13% Rh-Pr. In the case of such a battery configuration, the oxygen activity (% basis) a _p is given by the following equation (7) from the oxygen concentration electromotive force E (mV) and the molten steel temperature T (° C.). log a _p = 4.62−(13580−10.08E)/(T+273)
...(7) The molten steel composition at the end of blowing is C0.05%, Mn0.15%,
Assuming P0.02%, S0.010%, and O 0.06%, and using the value of the interaction coefficient (1600°C) of Sigworth et al., the oxygen activity coefficient f _p is f _p =0.962, It can be assumed that f _p ≈1, and therefore, equation (7) can be expressed as shown in equation (8) below. log O =8.62−(13580−10.08E)/(T+273)
...(8) Here, O is the oxygen potential in molten steel, and therefore, the oxygen potential in molten steel can be found from equation (8). FIG. 6 schematically shows an example of the overall configuration of a system for estimating molten steel composition at the end of blowing using the oxygen detection probe 1 using the oxygen concentration battery as described above. 6th
In the figure, a signal S _E of an oxygen concentration electromotive force E from an oxygen detection probe 1 immersed in molten steel in a converter 6 is input to an arithmetic processor 9 via an isolator 7 and an AD converter 8. Temperature T signal S _T from probe 1 is furnace side temperature recorder 10, AD
The signal is inputted to an arithmetic processor 9 via a converter 8. In this arithmetic processor 9, the oxygen potential O
are detected, and the concentrations of C, Mn, and P in the molten steel are calculated based on a predetermined correlation, and the estimated values are displayed on the display panel 11. It goes without saying that the data on the raw material charged to the converter is also input into the arithmetic processor 9 in advance. Furthermore, the oxygen potential in molten steel can be measured by using a stand-alone probe (immersion type probe) as mentioned above, or by incorporating an oxygen concentration battery into a sublance probe to perform other measurements at the same time. You can also measure it. In addition, since the P removal reaction is strongly influenced not only by the oxygen potential in molten steel but also by the slag state of the slag, the estimation accuracy can be improved by incorporating a parameter representing the slag state into the equation for estimating the P distribution ratio. can be achieved. In the case of a top-bottom blowing converter, furnace vibration is suitable as a parameter representing such a slag state. In other words, the converter furnace body vibration is
For example, as shown in FIG. 7, the amplitude is small at the beginning of blowing when the scrap is unmelted and the amount of auxiliary material input is small, but as the scrap is melted and the amount of auxiliary material input increases, the amplitude increases. Furthermore, as the slag becomes slag in the latter half of blowing, the stirring energy of the steel bath is absorbed by the slag layer, and the amplitude becomes smaller again. Therefore, by measuring the time from the moment when the amplitude of the furnace body vibration in the latter half of blowing falls below a certain value to the end of blowing and using it to estimate the P distribution ratio, it is possible to estimate the blow-end P concentration with extremely high accuracy. It becomes possible to estimate. For example, when measuring vibrations in a 250-ton class top-bottom blowing converter with a differential transformer connected to the furnace body, the amplitude is
It is sufficient to measure from the time when the thickness becomes 1.5 mm or less until the end of blowing. In the estimation method of this invention as described above,
Although it varies depending on the measurement conditions, normally the C concentration C _f is within ±0.5 × 10 ^-2 % compared to the chemical analysis value, and the phosphorus concentration P _f is also ±0.9, as is clear from the examples described later. ^Similarly , the manganese concentration Mn _f can be estimated within ±0.8×10 ^-2 %. In addition, since the components are estimated by detecting the oxygen potential and calculating from that value, it can be estimated in an extremely short time compared to chemical analysis. It can be shortened to about 20 seconds. Next, examples of this invention will be described. Example Molten iron containing 0.26% Si, 0.36% Mn, and 0.146% P
In blowing 271.1 tons using a top-bottom blowing converter,
In addition to hot metal as charging raw materials, 6.3 tons of scrap,
Burnt lime 7367Kg, fluorite 650Kg, iron ore 8492Kg,
Charged 2984 kg of raw dolomite, and the amount of oxygen used
Blowing was carried out at 13720 Nm ³ , and at the end of blowing, the C, P, and Mn concentrations in the molten steel were estimated using the system shown in Fig. 6 using the probe shown in Fig. 5. At this time, the oxygen concentration in the molten steel was 726ppm, the molten steel temperature was 1684℃,
The estimated amounts are C0.027%, Mn0.109%,
It was P0.0122%. On the other hand, a separate sample was taken at the end of the blowing process and chemically analyzed.
It was confirmed that the estimated values were very close to the chemical analysis values, with C0.028%, Mn0.11%, and P0.012%. As is clear from the above explanation, according to the molten steel composition estimating method of the present invention, the C, P, and Mn concentrations in molten steel can be estimated extremely quickly and accurately. As a result, the amount of corrosion of the converter refractory due to molten steel stagnation in the converter until tapping is reduced compared to the conventional method, and the serviceable charge number of the converter refractory is reduced. can be increased compared to the conventional method, and the effort conventionally required for sampling can be saved. Furthermore, according to the method of the present invention, since the Mn concentration at the blowing point can be accurately estimated, the amount of Mn-based ferroalloy to be charged into the ladle can be determined accurately. can be reduced (approximately 60%), and the C concentration can be estimated with high accuracy.
When adding Mn-based ferroalloy, the use of expensive low-carbon Mn-alloy ferroalloy and cheap medium-carbon Mn-alloy ferroalloy (Type 3 FeMn) can be carried out with greater accuracy, and additional effects such as contributing to a reduction in the unit price can also be achieved. can get.

[Brief explanation of the drawing]

Figure 1 is a correlation diagram showing an example of the correlation between the carbon concentration C _f in molten steel and the oxygen potential O in molten steel.
The figure shows an example of the correlation between the phosphorus distribution ratio L _P between slag and molten steel and the oxygen potential O in molten steel. Figure 3 shows the manganese distribution ratio between slag and molten steel.
Figure 4 is a correlation diagram showing an example of the relationship between L _Mo and _the oxygen potential O in molten steel; FIG. 5 is a schematic cross-sectional view showing an example of an oxygen detection probe incorporating an oxygen concentration battery used in carrying out the method of the present invention;
FIG. 6 is a schematic diagram showing an example of the overall configuration of a system for carrying out the method of the present invention, and FIG. 7 is an example of the measurement results of furnace body vibration in a top-bottom blowing converter.

Claims (1)

[Scope of Claims] 1. A method for estimating the composition of molten steel at the end of blowing when refining molten steel by oxygen blowing using a converter, which includes: The oxygen potential is measured, and the C concentration in the molten steel is estimated based on the correlation between the oxygen potential determined in advance and the C concentration in the molten steel.The Mn and P concentrations in the molten steel are estimated based on the previously determined C concentration. Oxygen potential and Mn between slag and molten steel
Based on the distribution ratio or correlation with the P distribution ratio
The Mn distribution ratio or P distribution ratio is estimated, and the estimated Mn distribution ratio or P distribution ratio, the amount of Mn or P contained in the charging raw material, and the molten steel weight and slag weight estimated from the charging raw material are calculated. A molten steel composition estimation method characterized by calculating Mn and P concentrations from .