JPS634010A - Refining method for bottom blow of steel in electric furnace - Google Patents

Abstract

PURPOSE:To complete slag making without purposely wind-up of electrodes at the early stage and to reduce Fe content in the slag by executing bottom blow of gas by the prescribed means, flow rate and pressure as indicator for rising height of molten steel surface. CONSTITUTION:Plural plugs 8 having plural fine tube holes 9 respectively at the furnace bottom are arranged. The gas is continuously or intermittently blown from these plugs 8 during the term from initial stage of refining period, when the charged scraps are melted down, to tapping off. The above gas blow is controlled at 1-40Nl/min per one fine tube hole 9 for the flowing rate, 20-800Nl/min per one plug 8 for the flowing rate and <=10kg/cm<2>.g the pressure. And, the rising height of molten steel surface 14 DELTAh is limited to <=1,000mm.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a bottom-blowing refining method for steel using an electric furnace. [Conventional technology and its problems] AC or DC arc electric furnaces are widely used as a means of melting and refining ordinary steel and alloy steel, but during the refining period after scrap melting, reactions between slag and metal, The movement of each component in the bath is controlled exclusively by diffusion rate.
For example, for P and S, each in molten iron is 2 X I
O-'aJ/s, 4 X 10-'aJ/s, respectively 4 X 10-'ad/s, 2 X in the slag
10-"a (/s). Therefore, the reaction between the slag and metal and the movement of each component in the steel bath are both slow, and the transmission of arc energy is restricted, which causes the following problems. ■There is no room for improving Fe yield.For example, if the total Fe content in slag is 20% and the amount of reslag per product copper is 50k.
g/T, 10 kg/T of iron migrates into the slag, causing loss. ■The temperature and composition of the slag and metal layer in the furnace tend to be uneven, and unmelted solids may remain until the final stage of smelting. ■Since the movement of component elements between molten steel and slag only diffuses little by little from the interface between slag and molten steel, the movement speed is likely to be insufficient, and the movement speed is likely to be insufficient.
,

[0] is also controlled by diffusion rate, so it takes a long reaction time. ■The arc energy is absorbed by the slag layer, and the action range of the arc heat is limited to a narrow area near the electrode.
Heat transfer is restricted and power consumption increases. ■The ferroalloy and deoxidizing agent are oxidized by the slag, and these additives, which should originally be used to reduce the metal, are consumed unnecessarily. In addition, recently, a method of injecting oxygen, oil, etc. from the furnace wall above the slag line has been widely adopted, but although this method is quite effective in promoting scrap melting, it cannot stir the steel bath. Therefore, it is hardly effective in efficiently transmitting arc energy and promoting metallurgical reactions. Recently, a so-called bottom-blowing method has been proposed in which gas is injected into the furnace from the hearth during operation of the electric furnace, but these methods do not have quantitative operational specifications and lack specificity. However, there are almost no examples of its adoption in actual operations. Recently, a method has been proposed in which a gas blowing pipe is installed at the lower part of the side wall of the electric furnace instead of at the bottom of the furnace, and inert gas is blown into the furnace during melting, and a large amount of inert gas and oxygen are blown into the furnace during refining. However, in this method, an excessive amount of gas is blown, and the electrode must be rolled up outside the furnace when blowing. Also, the appropriate amount and pressure of blowing are not specified, and a large amount of gas is blown into the furnace. Since gas is blown into the system, gas usage efficiency is poor and practicality is poor. [Means for solving the problems] The present invention was created through repeated research and experiments in order to solve the above-mentioned problems. During the refining stage of the electric furnace used in conjunction with the electric furnace, it is a practical method that allows the gas used to work most efficiently, strengthens the stirring power without necessarily requiring winding of the electrode, promotes metallurgical reactions, and improves energy efficiency. The object of the present invention is to provide this type of electric furnace bottom blowing refining method with high performance. In order to achieve this objective, the present invention quantifies the gas injection conditions from the bottom of the electric furnace, that is, the number of gas injection plugs, the injection amount, and the injection pressure, and controls the height of the molten steel rise within a predetermined range. It is something. In other words, the feature of the present invention is that from the beginning of the refining period, when the melting of the charged scrap is almost completed, until the steel is tapped, a , 1 to 4 ONQ/+m per capillary pore
In, 20 to 80 ONQ/win per plug, gas with a pressure of less than 10 kg/aJ・g is continuously or intermittently blown into the furnace, and the height of the rise of the steel bath is increased to 1000 m.
The aim is to control and operate within m. The present invention will be specifically described below based on the accompanying drawings. Figures 1 to 3 show an overview of the bottom-blowing refining method for steel after melting scrap using an electric furnace of the present invention, in which 1 is an electric furnace, and the furnace consists of an inner wall 2 of refractory material, a stamp, and a brick. It has a floor 3 and an iron skin 4 covering the outer periphery thereof, and an auxiliary burner or lance 5 is provided on the upper side wall. 6 and 6 are electrodes. Reference numeral 7 designates a special gas blowing device (one example) disposed at approximately equal intervals in the circumferential direction of the hearth 3. As shown in FIG. It comprises a plug 8 with a tapered head, a large number of thin tube holes 9, 9 drilled at predetermined intervals so as to pass through the plug in the height direction, and a distribution chamber 10 fitted into the lower end of the plug 8. , plug 8
is fitted into an opening in the hearth 3 and fixed by an additional construction brick 11, and the distribution chamber 10 is led to a gas supply source (not shown) by a gas plumber 2. Note that the metal tube for the thin tube hole is equipped with a mechanism to prevent the generation of induced current.
The drawings are omitted because they are not related to the present invention. 14 is molten steel, and 15 is slag. Therefore, the present invention provides a method for producing ordinary steel, alloy steel, or stainless steel using the electric furnace 1 while blowing gas into it.
In particular, the bottom of the furnace is
C08, air, oxygen, or an inert gas such as nitrogen gas or argon is continuously or intermittently blown into the furnace using the gas blowing device, and the bottom blowing of this gas is performed under the following conditions. It is. (2) Gas blowing is performed using a plurality of the gas blowing devices. ■ Regardless of the volume, the gas flow rate is 1 to 40 per capillary hole.
NQ/win, 20~80ON per plug
Let's say fi/Otoriin. (2) Keep the gas blowing pressure to less than 10 kg/aJ-. ■The above blowing flow rate and pressure are such that the height of the rise in the steel bath Δh is 1000+sm or less, preferably 50〈Δh×500 (
(mm). The above conditions mean that in an electric furnace with a relatively shallow bath depth (within approximately 1500 mm), during the refining period, the steel bath does not necessarily require winding up the electrodes, does not cause unnecessary cooling of the molten metal, and reduces the steel bath depth. This is a necessary condition for stirring most efficiently with the amount of gas, and the discovery of this is a feature of the present invention. To explain in detail, first, there is a plurality of gas blowing devices 7, and normally it is desirable to have no more than three.The reason is that if more than four gas blowing devices 7 are used, the surrounding hearth refractories will be damaged and it will be difficult to repair them. This is because it takes a lot of time to process, gives unnecessary movement to the steel bath, and has disadvantages such as impairing power efficiency. However, depending on the volume, up to 5 units may be installed. Thin tube hole 9 in each plug 8 of gas blowing device 7, 7
, 9 is generally 10 to 30, and the diameter of each capillary hole is preferably in the range of 0.6 to 1.5 m+m.
Moreover, the size of the capillary pores may be uniform or may be selected from those with different diameters. The reason why the thin tube hole was adopted is to obtain good penetration power (reaching distance) while dispersing the gas appropriately. The reason why the lower limit of the diameter of the thin tube hole is set to 0.6 mm is that a hole with a diameter smaller than this requires high pressure to introduce into the furnace the amount of gas necessary to provide stirring force. Set the upper limit to 1.
The reason why the weight is 5m is that the height of the molten steel bulge Δh is 1000
This is because II11 or less is the limit due to the correlation between the flow rate and pressure. Next, adjust the gas flow rate to 1 to 40 N Q/w per capillary hole.
The reason for in is 10 to 3 per plug as mentioned above.
When equipped with 0 capillary holes 9, I N per 1 capillary hole
If it is less than Q/+min, it will not be possible to prevent foreign matter, molten matter, and molten steel from entering the narrow tube holes, and the height of the molten steel bulge Δh will be insufficient during the refining stage, making it impossible to provide sufficient stirring force to the molten steel and slab. be. FIG. 4 shows the result of examining the relationship between the hole diameter and the limit flow rate for molten steel penetration at a molten steel depth of 1000+ m, and it can be seen that I N Q /rain or more is required in the above hole diameter range. In addition, the upper limit was set at 40 N 2 /win because at a flow rate exceeding this, melted material and molten steel will not enter the thin tube holes, but the melted material will scatter too much and adhere to the electrodes and furnace lid. Otherwise, the molten steel swell height Δh becomes excessively large, exceeding 1000+u+, and a large amount of molten steel scatters on the electrode, forcing complicated electrode winding. In addition, the gas flow rate per plug should be adjusted to 20 to 800 N.
The reason for setting Q/min is that in addition to the same reason as above, the total flow rate becomes too large and unnecessary cooling of the molten steel is promoted.
Furthermore, if an inert gas is used as the gas, the consumption amount will increase unnecessarily. Another feature of the present invention is that the gas pressure is limited to a low pressure of less than 10 kg/aJ-g. The lower limit is generally 1
kg/a#-g, and this is because the diameter of the nozzle is made small as described above, so even this level of pressure can prevent the intrusion of molten steel, and this is the lowest pressure at which the desired effects of the present invention can be obtained. The reason why the upper limit is set to less than 10 kg/dg is that sufficient effects can be obtained in the present invention at low pressure, and stirring more than necessary is meaningless. FIG. 5 shows the relationship between gas pressure and flow rate at a hearth thickness of 700 mm (=length of the capillary hole 9) for each diameter of the capillary hole. Also, Figure 6 shows the gas pressure 2 kg/a1
Figure 7 shows the relationship between the capillary hole length and flow rate when the gas pressure is 9.8 kg/aj-g. From these drawings and FIG. 4, it is possible to appropriately set simple and stable gas blowing conditions. Furthermore, the present invention adjusts the gas flow rate and gas pressure so that the height of the steel bath bulge Δh is 1000 mm or less, preferably 50<Δ
h (500 (m)), and the height of the rise in the steel bath Δh is set by the following formula: Δh=−H−E Here, H is the depth of the steel bath. ), E is the stirring force (watt) given to the steel bath by gas blowing, and K, α, and β are constants given experimentally. The depth of the steel bath in the electric furnace is 1500 mm or less, and in this case, α and β are experimentally determined to be 1.9≦≦2.9,
-1.40≦α≦-1,46, β: 2/3. and. The stirring power (watt) is given by controlling the gas blowing flow rate and pressure described above. Furthermore, even if a different factor from the above is used, for example, a different stirring energy equation,
The optimum range of the height of the bulge is 50 to 50 m, and the maximum value must be 1000 m or less. Figure 8 shows a conversion graph of steel bath depth H - stirring force E - steel bath swelling height Δh - gas flow rate per plug at constant bath temperature (1550°C). By making them for each temperature, you can easily set operating conditions. Normally, gas blowing should start from the time of charging the scrap, and at this time and when the scrap starts to melt, the pressure should be low enough to prevent clogging of the capillary holes by foreign objects and melted scrap; The gas blowing flow rate and pressure may be increased after waiting for a certain amount of melt to be generated, and the blowing flow rate and pressure may be gradually increased as the amount of generated gas increases. However, the regulation of the dimensions of the gas injection capillary hole, gas pressure, and gas flow rate detailed above is a condition for controlling the height of the molten steel to 10,001 or less during the refining period after scrap burn-through. Therefore, during the period when a considerable amount of unmelted material from the charged scrap remains, the material is present in the space between the slag line, the ceiling, and the inner wall of the furnace. Even if it is blown in, the molten material comes into contact with the unmelted charge present at the top during melting and is prevented from scattering, so there is no risk of it adhering to the electrode, electrode hole, inner surface of the ceiling, upper part of the furnace wall, etc. From the time of charging the scrap until almost the completion of melting,
Unless consideration is given to cooling the inside of the furnace by blowing inert gas in excess of the necessary amount, there is no need to particularly regulate the upper limits of the amount and pressure. After melting the scrap, the gas blowing flow rate and pressure are further increased to increase the height of the molten steel bulge Δh shown in Figure 3.
As a result, an appropriate stirring effect with just the right amount of stirring can be obtained, promoting the reaction between metal and slag, and making the temperature of the steel bath uniform. Figure 9 illustrates the operation pattern (molten steel depth, bottom blowing gas amount, and molten steel swelling height) in one charge of the present invention, where the gas consumption amount is 41.5 NM'/ch and the total stirring force is 0.165 KwH/ch. T was obtained. In addition, in the above-mentioned gas blowing, it is not necessary that all the plugs 8°8 have the same flow rate and pressure, and it is also possible to make the flow rate and pressure variable within the above range for each plug, and it is also possible to make the flow rate and pressure not continuous. , may be blown intermittently. [Example] The present invention will be explained in detail. The present invention was applied to manufacturing ordinary steel in a 50T electric furnace. Three plugs with 20 thin tube holes of 0.8 mm φ drilled in the bottom of the hearth are attached to the hearth of the hot zone at approximately 120° intervals, and from the time of charging scrap, the thin tube holes are made to prevent foreign matter from clogging. After pumping nitrogen gas under pressure and waiting for the formation of a small amount of dissolved material, 1.5N Q /win per capillary hole,
3ON Q/win per plug, pressure 1kg/a
Nitrogen gas was blown in at #·g, and the blowing flow rate was gradually increased in accordance with the increase in the amount of molten metal produced. 20ON per plug after scrap melting is completed
Q/win, nitrogen gas was blown at a pressure of 6 kg/cd·g, and the height of the molten steel buildup was controlled to 120 to 4,801 cm. The bath specifications for each time period are shown in Table 1 below. Table 1 The results of this operation (average value after multiple charges) are compared with the case without bottom blowing and are shown in Table 2 below. Note that the amount of molten steel was 45,450 kg. Table 2 also shows the oxidation phase elapsed time and basicity under the above operating conditions.
Comparative data of slag composition and molten steel temperature is shown in Figure 10.
This figure shows that according to the present invention, early slag formation is possible and a high basicity period can be maintained for a long time. Figure 11 shows the results of actual measurement of the variation in Cu content between products from the beginning of melting.
Because they are not mixed uniformly, there are large differences between sample periods. On the other hand, with Honzuke, uniform mixing conditions were established quickly and stable values were obtained. Figure 12 shows the changes in the ratio of (P) in slag and CP in melting over time after melting, and the change in the ratio of (S) in similar slag.
) and the change in the ratio of (S) during melting, and it can be seen that in the case of the method of the present invention, equilibrium is reached in a short time. In this example, the plug at the bottom of the hearth was installed at the hearth of the hot zone from the viewpoint of effective use of heat during the scrap melting period, but it can be installed at any position depending on the size and size of the electrode, the position, or the shape of the hearth bottom. As mentioned above, it goes without saying that gas can be blown from the position, and the type of gas is not limited to nitrogen. [Effects of the Invention] According to the present invention as described above, in electric furnace steelmaking, gas bottom blowing is carried out in the steel bath from the early stage of the refining period when the melting of charged scrap, oxidation, and reduction is almost completed until the steel is tapped. Using the height of the swelling as a guideline, we carried out the process using a specific blowing method, blowing flow rate, and pressure conditions, so we were able to reliably and stably obtain the following effects with efficient gas usage without having to wind up the electrodes. Can be done. Then, early slag formation becomes possible, undissolved CAO is reduced, and the high basicity period can be maintained for a long time, so that the CAOJ7X units can be reduced. Furthermore, during the refining stage, efficient stirring promotes the reaction between slag and metal, reducing the (TFe) content in the slag and thereby improving the tapping yield.
metal medium

[0] By reducing the content of deoxidizing agent, the yield of ferroalloy can be improved, and the uniformity of steel bath components can be promoted. Also, the steel bath temperature can be made uniform, and the melting and refining time can be shortened. Therefore, it is possible to improve production efficiency and save electricity.

[Brief explanation of drawings]

Fig. 1 is a schematic explanatory diagram showing the bottom blowing refining method of steel using an electric furnace according to the present invention, Fig. 2 is a plan view of Fig. 1, Fig. 3 is an enlarged view of Fig. Figure 5 is a graph showing the relationship between narrow tube hole diameter and molten steel penetration limit flow rate. Figure 5 is a graph showing the relationship between gas blowing pressure and flow rate. Figures 6 and 7 are graphs showing the relationship between narrow tube hole length and gas flow rate. Figure 8 is a graph showing the relationship between steel bath depth, stirring force, and height of molten steel at a constant temperature in the present invention, Figure 9 is a graph illustrating the operation pattern of the present invention, and Figure 10 is a graph showing the relationship between the steel bath depth and stirring force at a constant temperature in the present invention. A graph comparing the elapsed time of the oxidation period and basicity, slag composition, and molten steel temperature in the conventional method. Figure 11 is a graph examining the variation in Cu content between finished products from the time of melting. Figures 12 (a) (b) ) is a graph showing changes in the ratio of P and S in slag/molten steel with each elapsed time from burn-through. 3... Hearth, 8... Plug, 9... Capillary hole, Δh
...Height of molten steel rise

Claims (1)

[Claims] From the beginning of the refining period, when the melting of the charged scrap is almost completed, until the steel is tapped, from the plugs provided at the bottom of the furnace, each having a large number of thin tube holes, one to one
40Nl/min, 20-800Nl/per plug
An electric furnace characterized in that the electric furnace is operated by continuously or intermittently blowing gas into the furnace at a pressure of less than 10 kg/cm^2・g and controlling the height of the rise of the steel bath to within 1000 mm. A bottom-blown refining method for steel.