JPS6024312A - Method for managing refining of molten steel - Google Patents

Abstract

PURPOSE:To estimate easily, quickly and exactly the content of C in a molten steel and to refine efficiently said steel by blowing oxygen and C material into the molten steel in an arc furnace then continuing blowing of the C material alone and detecting the change in the quantity of the heat generated within the furnace. CONSTITUTION:Oxygen and C material are blown into the molten steel in an arc furnace 1 and after the temp. of the molten steel is quickly increased, the blowing of oxygen is stopped and the blowing of the C material is continued to reduce the FeO in the peroxidized state formed by blowing of oxygen. The end point of the reduction is detected by measuring the temp. of the furnace wall to know the change in the quantity of the heat generated in the arc furnace and the concn. of C in the molten steel is estimated as 0.10% C at the point of the time when the change shows a min. value. The content of C in the molten steel is estimated in accordance with the amt. of the C material blown thereafter. The above-mentioned measurement of the temp. of the furnace wall is preferably accomplished by measuring the change thereof with the temp. difference of the cooling water flowing into and from a water cooling box 2 provided in the upper part of the slag discharging port of the furnace 1.

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 consumption of raw materials and electric power by simply and quickly accurately estimating the C content in molten steel. Saze,
We provide technology that eliminates loss of operating time.

Regarding the refining of steel using an electric arc furnace, the applicant intends to reduce the electricity cost, which accounts for a large proportion of the cost, and to shorten the operating cycle. ,rCIJ We have developed and have already proposed a technology to reduce
No. 414).

In order to further enhance these effects, pure oxygen gas or oxygen-enriched air (hereinafter referred to as "oxygen") is used as the oxygen injected together with the C material, and an equivalent amount or more of oxygen is supplied to reduce the heat generated by oxidation of FO. This technology is also used to raise the temperature of molten steel, and we would like to disclose this as well (Japanese Patent Application Laid-Open No. 56-87617).
The so-called overoxidized state in which le is oxidized to Fe'O is, of course, disadvantageous in terms of raw material yield, and it is also undesirable that the amount of slag increases. However, the generated F
The eO is at least partially reduced by the subsequent injection of C material, and most of it is reduced if proper operation is performed, 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 is to pull back the /u peroxidized material as described above, and then reduce C to the desired level.
The goal is to increase the content. Regardless of the level of C content to be achieved, it is important to quickly and accurately grasp the C content in molten steel during work to avoid loss of power and raw materials, and waste of operating time. This is desirable in order to eliminate it. However, the C content was measured by collecting and analyzing molten steel samples.
Not only is it a hassle, but there are limits to how much time can be saved. Therefore, if there were a means that could more easily grasp the C content from moment to moment, the management of molten steel refining could be carried out more conveniently. Previously, the applicant measured the amount of heat carried away per unit time by the exhaust gas exiting from the reaction vessel during refining in which oxygen gas is blown into molten steel in a vessel to decarburize it, and from the change in the amount of heat, the amount of C content in the molten steel was determined. (Japanese Patent Application No. 136532/1983) to invent a technology for managing refining. this is,
Changes in the C content in molten steel affect the thermochemical reactions in the furnace, and the change in the calorific value is also equal to 1. Therefore, by keeping other conditions constant and tracking the calorific value, it is possible to This is based on the knowledge that changes in frl can be detected. Specifically, good results have been achieved by utilizing changes in the temperature rise of the shooter cooling water used to add alloying elements.

This time, we conceived and experimented with the idea of extending the above knowledge and applying it to arc furnace refining, and as we were successful, we would like to propose it here.

That is, the method for controlling molten steel refining of the present invention, when refining molten steel using an arc furnace, quickly increases the temperature of the molten steel by blowing oxygen and oxygen into the molten steel, and then stopping the injection of oxygen. Changes in the amount of heat generated in the arc furnace in a refining method in which the injection of C material continues, reducing at least part of the iron oxide produced by the injection of oxygen and increasing the C content in the molten steel to a desired level. The method is characterized in that the carbon content in molten steel is estimated based on the information.

It is possible to understand changes in the amount of heat generated within an arc furnace using various methods. One of these is to measure thirst on the furnace walls. Another method is to measure the heat load of the cooling water on the furnace wall. This is preferable since it does not require the addition of special equipment and provides highly accurate results.

Hereinafter, the process of establishing the present invention will be described in detail with reference to the latter measurement of the heat load of cooling water.

Now, let us assume that the overoxidized state of the molten steel mentioned above is (■), the stage where it is being pulled back is (■), the state where it has been eliminated is (■), and the stage where carburization has progressed is (■), then the heat generated by the reaction in the furnace A1 The arc loss heat B1 and the radiant heat C of the molten steel follow changes as shown by curves A1B and C in FIG. 1, respectively. The heat generated in the furnace is calculated by subtracting the endotherm due to the reduction from the heat generated by the oxidation of C-+CO→CO2 due to the reduction of Fe0->F(!), and becomes virtually zero when the reduction is almost complete. Arc heat loss increases due to a decrease in arc heating efficiency without a reduction in the amount of slag due to the reduction of FeO in the slag.

Radiant heat from molten steel also shows an increasing trend due to rising temperatures of molten steel and slag and a decrease in the amount of slag. in the end,
The heat transferred from the entire arc furnace to the cooling equipment (a) is
It is thought that the change will follow the change shown by curve T in the figure. The inventors predicted that the change in the amount of heat generated during this transition would be immediately reflected in the temperature difference between the cooling water inlet and outlet of the water cooling box, and this prediction was confirmed in actual operation.

Figure 2 shows an example of this, in which the difference in cooling water concentration gradually increases due to the injection of 02 and C materials, the temperature difference decreases when the 02 injection is stopped, reaches a minimum value, and then rises again. Turn. The values obtained by analyzing the C content in molten steel before and after this minimum value are shown in Fig. 2, and it can be seen that the temperature difference reaches its minimum value at around 0.10% C. Recognize.

On the other hand, when the blowing of 02 is stopped and the blowing of l is continued, the C content in the molten steel is naturally
It is determined by the amount of material, and it has been actually measured that there is a relationship similar to that shown in FIG. 3, for example. In other words, until the overoxidation state is completely eliminated, not much C remains in the molten steel because it is consumed by reduction of FeO and bonding with 0 in the steel, but from the point where the overoxidation state is completely eliminated, the amount of C injected increases. As a result, the C content increases. FIG. 3 shows a situation in which the C content in molten steel increases linearly depending on the amount of C material injected after the cooling water temperature difference has reached its minimum value. The relationship between the two differs depending on the alloy composition, bath temperature, amount of molten steel, injection speed, and other conditions, but once you understand it by actually measuring it in each case, there is no need to analyze samples from now on. can also be estimated quite accurately.

The heat load of the cooling water was measured using the double diagonal lined water cooling box 2, which is installed above the slag outlet, among the cooling equipment (water cooling box) of the J arc furnace 1, which is shown by diagonal lines in Fig. 4. It has been found that the most appropriate method is to measure the temperature difference between the inlet and outlet of the cooling water in what industrial engineers call a "jam cooler." The water-cooled box attached to the furnace wall slightly on the side is insensitive to the transfer of heat from the furnace, probably due to the large amount of water, and the water-cooled box around the auxiliary raw material input port is undesirable because it causes disturbance during input. The key is to choose a water-cooled box that is sensitive to and faithful to the heat generation of the entire furnace, and if this condition is met, a jam cooler is not necessary.

Similarly, when measuring the temperature of the furnace wall to understand changes in the amount of heat generated, the temperature varies depending on the location of the furnace wall, and the changes are also subject to various disturbances, so it is best to measure at multiple points. It is important to take advantage of the warm temperature of the eggs.

According to the present invention, refining of molten steel using an arc furnace,
When using the 02 enrichment-C injection method, the overoxidation state can be eliminated without analyzing the molten steel sample.
It can be immediately determined by continuous, simple and quick means such as measuring the temperature difference of cooling water, and the increased C content due to subsequent injection of C material can be accurately estimated without relying on sample analysis. This makes operations much 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 drawings]

Figure 1 shows the trend of heat leaving the furnace to the outside as the refining progresses by cause when the 02 enrichment-C injection method is adopted for refining molten steel in an arc furnace. 1-1 Conceptual graph It is. FIG. 2 is a graph showing a change in the temperature difference between the inlet and outlet of the cooling water of the arc furnace as the refining progresses for a certain example. FIG. 3 is a graph showing, for a certain example, the relationship between C material blowing and C content in molten steel after the cooling water temperature difference has reached a minimum value. FIG. 4 is for explaining the cooling equipment of the arc furnace, and A is a cross-sectional view and B is a side view. 1... Arc Furnace 2... Jam Cooler Patent Applicant Daido Steel Co., Ltd. Agent Patent Attorney Suga Sofuyori 1 Diagram ■ ■ ■ ■ Fang 8 Diagram 01234 C scale blow amount ( kg/l) Fang 411

Claims (6)

[Claims] (1) When refining molten steel using an arc furnace, oxygen gas or oxygen-enriched air (hereinafter referred to as "oxygen") and carbonaceous material (hereinafter referred to as "C material") are added to the molten steel. )
The humidity of the molten steel is quickly increased by blowing oxygen into the molten steel, and then the blowing of oxygen is stopped, but the blowing of C material is continued to reduce at least a part of the iron oxide produced by the oxygen blowing ii, and reduce the amount of carbon in the molten steel. A method for managing molten steel refining, which is characterized in that, in a refining method for increasing the content to a desired level, changes in the amount of heat generated in an arc furnace are ascertained, and the C content in the molten steel is estimated based on this. (2) The management method according to claim 1, wherein changes in the amount of heat generated in the arc furnace are ascertained by measuring the furnace wall temperature. (3) The management method according to claim 1, wherein changes in the amount of heat generated in the arc furnace are ascertained by measuring the heat load of cooling water on the furnace wall. (4) The heat load of the cooling water of the arc furnace is measured by tracking the degree of humidity increase of the cooling water flowing in and out of the water cooling box above the arc furnace slag outlet. Management method. (5) Any one of claims 1 to 3, which estimates the C content in molten steel to be about 0.10% when the heat (6) generated in the arc furnace shows a minimum value. How to manage it. (6) A patent for estimating the C content in molten steel based on the amount of C material injected into molten steel after the time when oxygen injection is stopped or the C content in molten steel is estimated to be 0.10%. A management method according to any one of claims 1 to 3.