JPH024653B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for estimating the oxygen concentration in molten steel, which continuously estimates the oxygen concentration in molten steel in vacuum deoxidation treatment after converter refining.

[Prior art] When molten steel tapped from a converter is subjected to vacuum deoxidation treatment in an RH degassing tank, etc., aluminum in the molten steel is
In order to control the amount of Al, it is necessary to understand the oxygen concentration of molten steel. For this reason, conventionally, an oxygen meter using a solid electrolyte has been used to measure the oxygen concentration of molten steel during deoxidation treatment.

[Problems to be solved by the invention] However, since this oxygen meter is expensive, when measuring the oxygen concentration in molten steel using a conventional oxygen meter that uses a solid electrolyte, it is difficult to deoxidize it. There is a problem that the processing cost is high.
Furthermore, since this oxygen meter cannot continuously measure the oxygen concentration, it is difficult to adjust Al with high accuracy, and it is also difficult to judge the appropriate deoxidation treatment time.

[Means for Solving the Problems] The present invention has been made in view of the above circumstances, and is a method for determining the oxygen concentration in molten steel, which allows continuous determination of the oxygen concentration in molten steel without using an expensive oxygen meter. The purpose is to provide a method for estimating oxygen concentration.

The method for estimating oxygen concentration in molten steel according to this invention is as follows:
In the vacuum deoxidation treatment of molten steel, at the beginning of the process, a carbon-containing substance is added to the overoxidized molten steel in several portions to bring the molten steel into a state close to equilibrium, and the carbon concentration [C] and carbon monoxide of the molten steel are reduced. The method is characterized in that the partial pressure P co and the temperature T are determined, and the oxygen concentration [O] of the molten steel is estimated based on these values and an equation showing the equilibrium relationship between the carbon concentration and the oxygen concentration.

This invention will be explained in detail below.

Since the molten steel after being tapped from the converter is in a superoxidized state, the oxygen concentration cannot be determined from the equilibrium equation. Therefore, in order to determine the oxygen concentration from the equilibrium equation, it is necessary to bring the molten steel into an equilibrium state. However, if an attempt is made to remove oxygen from the molten steel by adding a carbon substance, there is a risk that the molten steel undergoing vacuum deoxidation will boil, so this method has not been adopted in the past. However, the inventors of the present application have discovered that by dividing and introducing the carbon-containing material into small quantities several times, there is no danger of molten steel boiling even during vacuum processing, and safety is ensured. This invention was made based on such knowledge, and in this invention, first, when vacuum deoxidizing treatment is performed on molten steel, a carbon-containing substance is introduced into the molten steel in small amounts several times. do. As a result, the molten steel, which was in a superoxidized state at the time of tapping from the converter, returns to a state close to equilibrium.
[C] and [O] in molten steel can now be expressed by the following equilibrium equation (1).

log P co / [C] [O] = 1160 / T + 2.003 ... (1) Next, carbon concentration [C], carbon monoxide partial pressure P co
and find the temperature T. The carbon concentration [C] is the amount of carbon decarburized during the vacuum deoxidation treatment, based on the value obtained by adding the amount of carbon added during the vacuum deoxidation treatment to the amount of carbon before the vacuum deoxidation treatment determined by chemical analysis etc. (decarburization amount). By analyzing previous operational data, the relationship between various operational data and the amount of decarburization has been determined in advance. Therefore, the amount of decarburization can be estimated over time by processing various operational data during the operation. Moreover, the value of P co is the value of the pressure in the tank at that time. In vacuum deoxidation treatment, the vacuum deoxidation tank is maintained under high vacuum and most of the gas produced is CO, so P co can be regarded as the pressure inside the tank at that time. Further, the temperature T is a constant value determined for each type of steel.

Thereafter, at a predetermined period, the values of [C], P co and T are substituted into the above-mentioned equilibrium equation to calculate the oxygen concentration [O].
Continuously find.

[Embodiments] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Figures 1 and 2 show the vacuum deoxidation treatment time on the horizontal axis and the oxygen concentration on the vertical axis, and show the changes in oxygen concentration due to the vacuum deoxidation treatment time when the oxygen concentration was actually measured and when the oxygen concentration was estimated. FIG. 1 shows a first embodiment of the invention, and FIG. 2 shows a second embodiment of the invention. In the figure, black circles and solid lines indicate estimated values of oxygen concentration, and white circles and broken lines indicate actual measured values of oxygen concentration.

In the first embodiment, ferromanganese FMnH containing a certain amount of carbon and coke are used as carbon-containing substances, and 780 kg of FMnH and 21 kg of coke are converted into carbon amounts of about 20 kg every 30 seconds. It was divided into parts and poured into 300 tons of molten steel. In other words, 780 kg of FMnH containing carbon was poured into the molten steel in 5 parts immediately after 2 minutes and 30 seconds had passed from the start of deoxidation, and 21 kg of coke was poured into the molten steel 3 minutes after the start of deoxidation. The entire amount was added to increase [C], and oxygen was removed from the overoxidized molten steel to bring it into a state close to equilibrium. In this case, as shown in Figure 1, the actual measured value of oxygen concentration is approximately 260 ppm at the early stage of deoxidation treatment when the degree of peroxidation of the molten steel is high.
At 3 minutes after the start of deoxidation, it is about 130ppm, at 5 minutes it is about 100ppm, and at 9 minutes it is about
It is gradually decreasing to 70ppm. on the other hand,
The estimated value of oxygen concentration is approximately 160 ppm at the beginning of deoxidation, which is lower than the actual value, but it gradually approaches the actual value and reaches approximately 160 ppm by 3 minutes after the start of deoxidation.
90ppm, after 5 minutes it becomes about 85ppm, and in the end,
When 9 minutes have passed after the start of deoxidation treatment, it is about 70ppm,
The values were shown to be approximately in agreement with the actual measured values.

In the second example, as in the first example, a certain amount of carbon was contained as the carbon-containing substance.
Using FMnH and coke, 600Kg of FMnH and
64 kg of coke was divided into approximately 20 kg of carbon every 30 seconds and poured into 300 tons of molten steel. In other words, by the time 2 minutes have passed from the start of deoxidation
600Kg of FMnH was divided into 4 parts and poured into the molten steel, and 64 kg was added 3 minutes after the start of deoxidation treatment.
Kg of coke is divided into three parts and poured into molten steel.
Oxygen was removed from the overoxidized molten steel to bring it to a state close to equilibrium. In this case, as shown in Figure 2, the actual measured value of oxygen concentration is approximately 180 ppm at the beginning of deoxidation treatment when the degree of peroxidation of the molten steel is high, but it is approximately 100 ppm at 3 minutes after the start of deoxidation, and after 5 minutes. After 8 minutes, it was about 60ppm, and after 8 minutes it was about 45ppm, gradually decreasing. On the other hand, the estimated value of the oxygen concentration is approximately 130 ppm at the beginning of deoxidation, which is lower than the actual value, but gradually approaches the actual value and reaches approximately 60 ppm and 5
After 8 minutes had elapsed from the start of the deoxidizing treatment, the value was about 45 ppm, and finally, after 8 minutes had passed from the start of the deoxidizing treatment, it was about 40 ppm, showing a value that almost coincided with the actually measured value as in the first example.

Based on the above results, at the initial stage of vacuum deoxidation treatment,
Although there is a difference between the estimated value and the actual measured value of the oxygen concentration in molten steel, the state gradually approaches an equilibrium state, and after a predetermined period of time has passed after the start of deoxidation treatment, the estimated value and the actual value of the oxygen concentration in molten steel will be different. It can be seen that they almost match.

In Fig. 3, the horizontal axis represents the oxygen concentration estimated by the oxygen concentration estimation method in molten steel according to the present invention, and the vertical axis represents the actually measured oxygen concentration, and the relationship between the estimated value and the actual measured value of the oxygen concentration is plotted. FIG. 2 is a graph diagram comparing the case where a carbon-containing substance is added during vacuum deoxidation treatment (white circles) and the case where it is not added (black circles). According to this, for the products to which carbon-containing substances were added during vacuum deoxidation treatment, the estimated oxygen concentrations were all within ±20 ppm of the actual values, but for the products to which carbon-containing substances were not added. The estimated value is lower than the actual value by ±20ppm.
It can be seen that there are many things that fall outside of this range. This shows that the estimated value approaches the actual value by adding a carbon-containing substance to the molten steel in the deoxidizing treatment.

In Figure 4, the horizontal axis shows the carbon concentration estimated by this invention, and the vertical axis shows the actually measured carbon concentration.
Chemical analysis of initial carbon concentration (black circles) and
It is a graph diagram showing the estimation accuracy of carbon concentration for those subjected to luminescence analysis (white circles). According to this, when the carbon concentration is estimated by chemically analyzing the carbon concentration before vacuum deoxidation treatment, an estimated value that is extremely close to the actual measurement value can be obtained. On the other hand, when the carbon concentration is estimated by luminescence analysis of the carbon concentration before vacuum deoxidation treatment, the estimated value tends to be larger than the actual value, and this tendency is particularly noticeable around 50 ppm.
For this reason, it is preferable to determine the initial carbon content by chemical analysis.

[Effects of the Invention] According to the present invention, since an oxygen meter using an expensive solid electrolyte is not required, operating costs in the vacuum deoxidation process can be reduced. Furthermore, after a predetermined period of time has elapsed after the addition of the carbon-containing substance, the estimated value of oxygen concentration matches the measured value with high precision, making it possible to estimate the oxygen concentration over time with high precision during vacuum deoxidation treatment. . Therefore, when the oxygen concentration is high, carbon-containing substances are added to the molten steel to reduce the oxygen concentration, and at the end of the deoxidation treatment,
Oxygen concentration can always be maintained at a low level. This makes it necessary to add after vacuum deoxidation treatment.
The amount of Al is reduced and the cost of addition is reduced. Furthermore,
Since the oxygen concentration can be continuously monitored with high precision during vacuum deoxidation treatment, the appropriate deoxidation treatment time can be determined, contributing to operational stability.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between vacuum deoxidation treatment time and oxygen concentration in the first embodiment of this invention, and FIG. 2 is a graph showing the relationship between vacuum deoxidation treatment time and oxygen concentration in the second embodiment of this invention. Figure 3 is a graph showing the accuracy of oxygen estimation when carbon-containing substances are added and not added to molten steel in vacuum deoxidation treatment, and Figure 4 is the accuracy of estimation of carbon content. FIG.

Claims (1)

[Claims] 1. At the initial stage of vacuum deoxidation treatment of molten steel,
Carbon-containing substances are added to overoxidized molten steel in several portions to bring the molten steel into a state close to equilibrium, and the carbon concentration [C], carbon monoxide partial pressure Pco, and temperature T of the molten steel are determined, and these values are calculated. A method for estimating oxygen concentration in molten steel, the method comprising estimating the oxygen concentration [O] of molten steel based on: