JPS60181216A - Method for controlling refining of molten steel - Google Patents

Abstract

PURPOSE:To make operation easy in the stage of blowing gaseous O2 and carbonaceous material into a molten steel by using an arc furnace and refining the molten steel by tracing the transition of the temp. of the waste gas from the arc furnace and estimating exactly the content of C in the molten steel. CONSTITUTION:Gaseous O2 increases quickly the temp. of a molten steel when the air enriched with O2 and carbonaceous material are blown into the molten steel in refining of the molten steel using an arc furnace. Blowing of the O2 is then stopped and blowing of the carbonaceous material is continued to reduce part or more of the FeO formed by blowing of the gaseous O2 and to increase the content of C in the molten steel up to a desired level. The point when the content of C in the molten steel attains 0.10% is exactly estimated by measuring the temp. of the waste gas from the arc furnace without analyzing the sample of the molten steel. This method is executed easily and quickly and the operation is made extremely easy. The wasteful operation time is eventually eliminated, the consumption of electric power and material is improved and the variance in the content of C of the product steel material is decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for managing molten steel refining using an arc furnace, and improves the basic unit of raw materials and electric power by simply, quickly and accurately estimating the C content in molten steel. We provide technology that eliminates loss of operating time.

Regarding the refining of steel using an arc furnace, the applicant proposes to use air or oxygen and carbonaceous materials in molten steel for the purpose of reducing electricity costs, which account for a large proportion of costs, and shortening the operation cycle. (hereinafter referred to as "0 month") (this will not be referred to as [C-injection])
, as well as promoting temperature rise due to the heat generation associated with combustion from c to co,
We developed a technology that reduces heat loss by foaming slag with the generated CO gas and enveloping the arc with it.
This has already been proposed (Japanese Unexamined Patent Publication No. 5Fj-89414).

In order to further enhance the 1c effect, pure oxygen gas or oxygen-enriched air (hereinafter referred to as 1
This technique was also disclosed (Japanese Patent Application Laid-Open No. 87617/1983) in which the heat generated by oxidation of Fe is also used to raise the temperature of molten steel by supplying an equivalent amount or more of oxygen using a molten steel (represented by M cable).

The so-called overoxidized state in which Fe is oxidized to FeO is of course disadvantageous in terms of raw material yield, and it is also undesirable that the amount of slag increases. However, the generated Fe
O is at least partially reduced by the subsequent blowing of C material, and most of it is reduced if proper operation is carried out, and the overoxidized state is eliminated by returning to Fe.

In this improved technique, the ratio of C and 02 injected into the molten steel is made to be in excess of 02 based on the equivalence relationship, so that the C content in the molten steel gradually decreases. As mentioned in the above disclosure, the rate of decrease of C in molten steel is approximately 0.10
%, above which the reaction rate is rate-limiting, and below it is diffusion rate-limiting.

The refining operation consists of pulling back the peroxidized material as described above and then increasing the C content to the desired level. Regardless of the level of C content that should be reached, it is important to quickly and accurately grasp the C content in molten steel during work, to avoid the loss of electricity and raw materials, and to reduce operating time. This is desirable in terms of eliminating waste.

However, measuring the C content by sampling and analyzing molten steel lean pull is not only troublesome, but also limits the amount of time it can save.

Therefore, if there were a means to more easily grasp the C content from time to time, the management of molten steel refining could be carried out more conveniently.

In the refining process in which oxygen gas is blown into the molten steel to decarburize it in Betzler, the applicant has proposed that the amount of heat carried away per unit time by the exhaust gas emitted from the reaction vessel can be absorbed into the cold 11 water of the chute for adding alloying elements. He invented a technique for controlling refining by measuring the C content in molten steel by measuring it using changes in temperature rise (Japanese Patent Application No. 57-136532).
This is because changes in the C content in the molten steel affect the thermochemical reactions in the furnace, resulting in changes in the calorific value, so by keeping other conditions constant and tracking the calorific value, the above 5-C This is based on the knowledge that changes in content can be detected.

Subsequently, the applicant clarified that this knowledge could be applied to arc furnace refining, and had already proposed it (Japanese Patent Application No. 58-1).
No. 313155). Changes in the amount of heat generated in an arc furnace can be ascertained by measuring the heat load of the cooling water on the furnace wall, especially the cooling water on the cooling jacket called a "jam cooler."

As a result of further research, it was discovered that by tracking the change in exhaust gas temperature from the arc furnace, the C content in molten steel can be estimated based on it, leading to the present invention.

The method of controlling molten steel refining of the present invention is that when refining molten steel using an arc furnace, oxygen and C material are injected into the molten steel to quickly raise the temperature of the molten steel, and then the injection of oxygen is stopped, but C The blowing of the material continues, reducing at least a portion of the oxygen iron produced by the blowing of oxygen, and increasing the C content in the molten steel to a desired level. The present invention is characterized in that the C content in molten steel is estimated based on the lft shift of .

The present invention is theoretically based on the following considerations.

In other words, a large amount of CO gas generated by reduction of Fe0f7) in the slag increases (2) The exhaust gas temperature rises in proportion to it, and therefore, from that degree, Fe0f7) in the slag
The idea is that the C content can be estimated from the equilibrium relationship between eO in the slag and C in the molten steel.

This is conceptually shown in Figure 1. When C-injection is performed in an arc furnace where the f-eo% in the slag and the C% in the molten steel are around A in the figure, F
The equilibrium of eo/C moves along the curve ``-'' toward B. As mentioned above, since the reaction is rate-limiting when C=0.10% or more J-, Fe0% becomes almost constant after 8 points despite the 0% increase.

This fact has been experimentally confirmed, and FIG. 2 shows it. Although the position of the curve differs depending on the composition of the steel, it all shows the same tendency as shown in Figure 1.

The reason why the temperature of gas 11 increases as the amount of CO gas produced increases is simply because the heat of combustion thereof increases. ! l-, the exhaust gas temperature will follow the course as shown in FIG. 3 as the refining time progresses. That is, due to C-injection, the C content in the molten steel increases, and the CO generated from the W of FeO in the slag is combusted and the exhaust gas temperature rises, but Fe0(7)3! As the rate decreases as the concentration progresses, the temperature rise also slows down, and when C = 0.10% is exceeded and the reaction rate is limited, the amount of CO produced reaches a plateau and begins to decrease as FeO decreases, and the exhaust gas temperature decreases. It will start to show a downward trend after hitting a plateau.

The validity of this idea was also confirmed through experiments. 1
In other words, as shown in Figure 4, in the arc furnace refining of 80M440 steel, the exhaust gas temperature reaches its maximum value shortly before stopping C-injection after stopping oxygen injection, and the sample when that point is reached. has a 0-containing slope of 0.
It was within 10%. In addition, the three regions of exhaust gas temperature in Fig. 3 are A... Rising process B... Within 5°C from the maximum temperature C...
The distribution of C content in the molten steel samples taken during each descending process is as shown in FIG. Region B, that is, the region where the exhaust gas temperature is within 5°C from the maximum temperature, and C = 0.1
It is clear that the range corresponds to 0±0.02%.

This shows that it is not a mistake to estimate C=0.10% at the point where the temperature of the exhaust gas reaches its highest point. Needless to say, reaching the maximum temperature is the point at which the rate of change in temperature has decreased to zero, so by continuously measuring the rate of change, it can be known with a very small delay.

However, in actual operations, we must be aware of the fact that the trends in exhaust gas humidity vary somewhat depending on the operating conditions9- and that the hour at which the maximum temperature occurs tends to vary slightly. No.

First, the rate of C-injection, that is, the amount of C material injected into a certain amount of molten steel and slag per unit time has an effect on the change in exhaust gas temperature. When this relationship was actually measured, the results shown in FIG. 6 were obtained.
As shown in the figure, the higher the C-injection rate, the higher the maximum temperature, but the effect is not so great that the curve in the figure (the solid line F) becomes like that. There was a large effect on the temperature rise and fall, and a relationship as shown by a straight line with a steep slope (dashed line) was observed.

In addition to this, there is an effect of the oxygen blowing rate, which is introduced before or at the same time as the C material.

The results of actually measuring the relationship with the temperature increase rate are shown in FIG.

Therefore, in implementing the present invention, the oxygen blowing rate and C-injection rate should be selected depending on the capacity of the arc furnace and the compositions of the steel and slag. In any case, under certain operating conditions, how does the change in exhaust gas temperature and the C content in molten steel have a 4T relationship centered on the connection between the maximum temperature and C = 0.10%? It is necessary to experimentally confirm N1 (J), but once you have confirmed it, you can track the change in exhaust gas temperature from now on.

After the C content in the molten steel exceeds 0.10%, the 0 content in the molten steel increases linearly depending on the amount of C-injection. The pattern is as shown in FIG. 8, an example of which is shown in FIG. Therefore, steel with a desired C content can be easily obtained.

Although the method of the present invention can be applied to M refining of any steel, it is advantageous for producing steel in a relatively low carbon region of C50.40% as a common feature of the oxygen blowing/C-injection refining method. It is. This is because the C content is extremely reduced by blowing in oxygen, and a large amount of C-injection is required to transfer it to the carbon region.

The sharpener according to the present invention is capable of refining molten steel using an arc furnace.
02 Enrichment - Implementation using the injection method, the point at which C in molten steel reaches 0.10% can be determined by continuous, simple and quick methods such as measuring the temperature of exhaust gas without analyzing molten steel samples. Since the C content increased by the subsequent blowing of 044 can be accurately estimated without relying on sample analysis, the operation becomes significantly easier. As a result, there is no wasted operating time, the unit consumption of electricity and materials is improved, and the variation in C content of product steel can be reduced.

[Brief explanation of the drawing]

1 and 2 are graphs showing the relationship between the FeO concentration in slag and the C content in molten steel.
The figure shows a conceptual trend, and Figure 2 is based on experimental values. Figures 3 and 4 are both graphs showing the relationship between the R time and the flue gas temperature transition in arc furnace refining, with Figure 3 showing a conceptual trend, and Figure 4 Figure 4 is based on experimental values. Figure 5 is a histogram showing the distribution of C content in molten steel in each region of Figure 3. Figure 6 shows that the C-injection speed is Fig. 7 is a graph showing the influence of the maximum temperature reached on the temperature rise rate of the exhaust gas. This is a graph showing the relationship between C-injection and C content in the region exceeding c=o,io% in molten steel.Patent applicant Daido Steel Co., Ltd. Agent Patent attorney Suga Sofu = 13- Mai"p < rd -m 〆

Claims (3)

[Claims] (1) When refining molten steel using an arc furnace, oxygen gas or oxygen-enriched air (hereinafter referred to as "II element") is added to the molten steel.
The temperature of the molten steel is quickly raised by blowing carbonaceous material (hereinafter referred to as "C material"), and then the blowing of oxygen is stopped, but the blowing of C material continues, and the oxygen In a refining method that reduces at least a portion of iron oxide produced by blowing and increases the C content in molten steel to a desired level, the C content in molten steel is reduced based on changes in the exhaust gas temperature from the arc furnace. A method for managing molten steel refining characterized by estimation. (2) The pipe Il of claim 1, in which the C content in the molten steel is estimated to be approximately 0010% when the temperature of the exhaust gas from the arc furnace reaches the maximum temperature. Law. (3) Claim 1, which estimates the C content in molten steel based on the amount of C material injected into the molten steel after the time when the C content in the molten steel is estimated to be 0.10%, or Second
How to manage the section.