JPS6360089B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for refining pig iron in a top-blown, top-bottom-blown or bottom-blown converter, and particularly to a converter steel manufacturing method that suppresses slopping. [Prior Art] A conventional method for suppressing slopping, which significantly impairs the stability of converter refining, is to lower the top blowing lance to achieve hard blowing, as disclosed in Japanese Patent Application Laid-Open No. 131306/1983, for example. Forming method and reducing the amount of gas generated by lowering the top blowing oxygen flow rate. There was a way to wait for the slag to subside, but if it still did not subside, the blowing process would have to be interrupted. As a means to avoid this interruption, in addition to the suppression method by changing the top-blowing acid conditions, for example,
As disclosed in Publication No. 57-143415, a method is used in which a sedative is introduced into the furnace from the outside. Limestone, raw dolomite or paper sludge aimed at degassing and cooling the slag.
There are ogalites, etc., and carbon-based substances that aim to reduce the viscosity of slag by reducing the slag while generating gas. [Problems to be Solved by the Invention] As mentioned above, conventional methods for suppressing slopping include (1) using upper insufflation conditions, and (2) introducing sedatives after slopping occurs. First, method (1) lowers the height of the lance to reduce the amount and rate of FeO produced at the hot spot, thereby reducing the forming process. Suppressing the viscosity of slag,
This is intended to prevent the occurrence of slopping, and also to reduce the rate of oxygen delivery and reduce the amount of CO gas that causes forming, thereby suppressing sloping. However, there is a problem in that the effect of suppressing sloping by manipulating the lance height and changing the amount of oxygen supplied is small, and furthermore, it is impossible to prevent sloping from occurring suddenly during blowing. Next, among methods (2), for example, limestone, raw dolomite, paper sludge. Forming is done by adding Ogarite etc. The method of generating gas in the slag to break bubbles and calming the slag may not work, but depending on the properties of the slag, especially its viscosity, the gas generated by adding these substances may be used to promote foaming. However, the effect is unstable, and this method also has the problem that if the prediction of sloping is insufficient, it is impossible to suppress sloping in advance. Also, among methods (2), forming. In the method of suppressing slag by reducing slag, if a carbon-based substance such as coke or coal is added as a suppressant at a rate of 1 to 5 kg/T-S when slopping occurs, molten steel contamination ([S ], [N]), and if expensive low-S carbon substances are added, there will be no contamination of molten steel, but it will be necessary to strengthen the preliminary desulfurization of hot metal, leading to an increase in melting costs. There is. [Means for Solving the Problems] In order to solve the above-mentioned problems of the conventional method for suppressing slopping in converter refining, the present invention provides a method for simultaneously introducing a gas generating substance and a slag reducing substance into the furnace during blowing. The method is to add The above means will be specifically explained below. (1) Limestone, raw dolomide, coke, coal, etc. are effective as gas generating substances for slopping suppression, and coke, coal, etc. as slag reducing substances. When limestone and carbon-based materials, which are normally used in blowing, are added to the furnace at the same time or in a mixed state, the amount of slag added is approximately 100 kg/T-S (steel) in normal blowing. It may be determined based on a certain thing, and in slagless blowing, etc., the amount of generated or residual slag is made into a table for each blowing condition based on the blowing results, and the predicted amount of target slag for each blowing condition is understood and added. The amount may be determined. As an example, Fig. 1 shows actual test results for each addition amount in normal blowing of 100Kg/TS. In the range shown by the shaded area A in this figure, where the slopping suppressing effect is achieved, the amount added is 5 kg/TS or more for limestone as a gas generating substance, and 0.5 kg/TS for coke as a slag reducing substance, that is, a carbon-based substance. It can be seen from this figure that the above is effective. In the case of limestone, the upper limit of the amount added is shown as C in Figure 1, and is determined based on the cooling status of the steel bath by adding limestone, constraints on the heat source in the converter, and the total amount of CaO required for refining, and in the case of coke. is indicated by B in FIG. 1, and since [S] and [N] increase by adding it, it is determined by the hot metal conditions and the required components of the steel to be melted. The amount added (input amount) is preferably kept to the minimum necessary from the viewpoint of economy and workability. Also, the ratio of the amount added between each additive is
It is effective to set the amount of coke/the amount of limestone to 0.1 to 5.0, although the reason is not clear, and it is necessary from the viewpoint of operability that the feeding rate be 100 Kg/min to 1000 Kg/min. The method of adding and charging the slag may be free fall from a hopper above the furnace, injection into the slag by pneumatic conveyance, etc., and there is no practical difference in the effect. In addition, the particle size of the carbon-based material that is the slag reducing material is preferably 10 to 30 mm from the viewpoint of reduction efficiency, handling, and operability. (2) In the present invention, the timing of adding additives is the period when slopping occurs in the early to middle stages of blowing, when the so-called [Si] blowing shifts to the peak decarburization stage, and the second half of the peak decarburization stage in the middle stage of blowing. Focusing on the fact that it mainly occurs in the second stage, we investigated whether or not there was a tendency for slopping to occur during one or both of the periods of 20% to 35% and 40% to 60% of the required oxygen supply amount during blowing. However, it is always necessary to add the aforementioned limestone and coke to the furnace. [Effect] The slopping phenomenon in converter refining is caused by the oxidation and removal of CaO-based auxiliary raw materials added into the furnace as a slag-forming agent (SiO ₂ ), (FeO), and (MnO).
etc., to form a low melting point substance and become a so-called slag state, the (FeO) or (MnO) in the slag increases and the viscosity of the slag decreases, and the viscosity decreases from 2 centipoise to 20 centipoise. When the temperature is within the centipoise range, carbon in the hot metal is oxidized and produced.
When CO gas is generated, the low melting point slag foams and forms without bursting, causing the slag to overflow or eject from the furnace mouth. In other words, when the viscosity of the slag is less than 2 centipoise or exceeds 20 centipoise, the forming phenomenon that leads to the well-known sloping phenomenon is no longer observed. In the present invention, limestone (CaCO ₃ ) and a carbon-based substance are added to the slag at the same time at the beginning or middle of the blowing process, when the above-mentioned foaming is generated, and the carbon-based material is explosively added to the slag.
Generates CO gas to promote bubble breakage and
Forming is achieved by reducing (FeO) in the slag by the carbon in the additive. The viscosity of the slag is brought to a range exceeding 20 centipoise to suppress the forming phenomenon of the slag in the furnace. That is, in the present invention, due to the synergistic effect of the foam-breaking promoting effect of limestone and the formation of a non-forming region of slag viscosity by the carbon-based material, the problem of non-foam-breaking slag generation when limestone alone is used is solved, and It was possible to avoid the risk of contamination of molten steel, which is a problem when carbon-based substances are used alone. [Example] Using a melt gun having the composition shown in Table 1, blowing was carried out to obtain molten steel having the composition and temperature shown in Table 2.

【table】

[Table] At that time, top-bottom blown refining was performed under the conditions shown in Figure 2 (line C shows the amount of oxygen blown at the bottom, line D shows the amount of oxygen blown at the top and bottom) (the distance between the lance mouth and the hot water surface was 4 m). certain),
The results shown in Table 3 (inventive example) and Table 4 (conventional example) were obtained.

【table】

〔Effect of the invention〕

According to the present invention, a gas generating substance and a slag reducing substance are added to the furnace during blowing, thereby effectively preventing slopping without contaminating the molten steel. This will improve iron yield, improve productivity,
It has great industrial effects, such as the ability to reduce manufacturing costs.

[Brief explanation of the drawing]

Figure 1 is an experimental result diagram showing the range of the optimal input amounts of limestone and coke in the present invention, and Figure 2 is
It is an explanatory view of blowing conditions of an example of the present invention and a conventional example.

Claims (1)

[Claims] 1. In top-blown, top-bottom-blown, or bottom-blown converter refining, 20 to 35% and 40 to 60% of the required oxygen supply amount during blowing.
%, at the same time with a coke amount/limestone amount of 0.1 to 5.0.
A method for suppressing slopping in a converter, characterized by adding slag to the furnace slag at a rate of 100 to 1000 kg/min.