JPS62139809A - Method and apparatus for refining molten steel under reduced pressure - Google Patents

Abstract

PURPOSE:To suppress the bumping of a molten steel in the stage of refining the molten steel under a reduced pressure by controlling the pressure in a vacuum vessel and the change rate of a decarburization rate with age in such a manner that the CO and CO2 generated from the molten steel do not attain a satd. state. CONSTITUTION:A ladle 2 contg. the molten steel 3 is set in the vacuum vessel 1 and the molten steel 3 is stirred by oxygen blowing from a lance 5 and the Ar blown from a porous plug 4 by which the molten steel is refined. The pressure in an exhaust gas path 6 and the CO and CO2 in the gas are measured by a pressure gage 8 and an analyzer 9 in this stage. The signal obtd. by processing the value which is the result of the subtraction of the measured value from the preset vacuum degree pattern set in a vacuum degree pattern setter 10 with a proportional integrator 12 and the signal obtd. by subtracting the change rate pattern set in a setter 11 for the pattern of the change rate of the decarburization rate with age from the change rate of the decarburization with age determined by the gas analyzer 9 and processing the result thereof with a proportional integrating differentiator 14 are added in an adder 13. The vacuum degree of a pressure reducing means 7 is so regulated as to increase the pressure in the vacuum vessel 1. The generation of the bumping of the molten steel by the CO and CO2 and the consequent overflow from the ladle 2 are thus prevented.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a method for refining molten steel under reduced pressure, which improves operability by suppressing the bumping phenomenon of molten steel, which is a problem when refining molten steel under reduced pressure, and an apparatus for carrying out the method. .

[Conventional technology]

In recent years, a method commonly known as the vOD method, in which molten steel is poured into a ladle placed in a vacuum vessel, the pressure inside the vacuum vessel is reduced, and oxygen gas is blown upward while stirring the molten steel in the ladle with an inert gas such as argon gas. The refining power of /8 steel, which is 4, allows the decarburization reaction to progress aggressively to produce ultra-low carbon steel, as well as degassing processes such as dehydrogenation and denitrification through CO boiling etc. that accompany decarburization. It is becoming more and more widely implemented as it can effectively advance the process. However, in the 't81JA refining method under reduced pressure, active co-boiling occurs at the beginning of the work to evacuate the vacuum vessel, and molten steel flows out of the ladle due to spitting. This has become a very serious problem in the refining of molten steel. The cause of spitting is generally that the composition and temperature of the molten steel before vacuum refining are not appropriate, that the molten steel has a very high FJ, or that there is a lot of slag mixed in. This becomes noticeable when the slag contains a large amount of metal oxide or when the oxygen blowing conditions under reduced pressure are honey blowing. For this reason, in the past, the following measures were taken: - Keep the liquid level of the molten steel sufficiently lower than the top of the steel so that the molten steel does not flow out into the steel draw even if spitting occurs; - Vacuum container to store the steel draw The only measures taken were simply adjusting the means to depressurize the inside and slowing down the rate of decompression as much as possible.

[Problems to be solved by the invention]

However, if such a method is implemented in the refining of molten steel under reduced pressure, the first method described above will reduce the amount of molten Tl4m
However, a very large steel stock for refining is required, and a correspondingly large vacuum container for storing the steel stock is required, which is extremely uneconomical and unsuitable for practical use. In addition, in the second method described above, although the means for reducing the pressure inside the vacuum container has a large capacity, it is operated at reduced capacity, which not only increases the operating time and results in inefficiency, which is not only undesirable. , target carbon depending on the steel type, however,
Since the composition of molten steel, slag composition, weight of molten steel, other metals added and their amounts are different, CO naturally occurs. Since the refining conditions vary depending on the length of the refining process, it is necessary to set the degree of depressurization according to the various refining conditions, and it is said that if the degree of depressurization is not changed for steel types that have a certain degree of decompression, the work efficiency will further decrease. There was a problem.

[Means for Solving the Problems 1] The present inventors have conducted various studies to solve the above problems, and have found that the occurrence of the bumping phenomenon of molten steel during spitting is caused by saturation corresponding to the pressure inside the vacuum vessel. The above co, co
, it was determined that most of the reaction occurred due to the reaction occurring in the molten steel, and the pressure in the vacuum vessel was controlled so that the CO generated from the molten steel did not reach a saturated state, and the decarburization of the molten steel was carried out. Focusing on the fact that it is only necessary to control the rate of change in velocity over time, they have completed a method for refining molten steel under reduced pressure and an apparatus for carrying out the method according to the present invention. That is, in the present invention, when refining molten steel using a vacuum ladle degassing device, the pressure of the exhaust gas path connected to the vacuum container is measured and gas analyzed, and the measured pressure is subtracted from a preset vacuum degree pattern. The value of the sum of the positive value processed signal and the positive value processed signal obtained by subtracting the preset pattern of decarburization rate change over time from the rate of change over time of decarburization rate determined by gas analysis. The present invention provides a method for refining molten steel under reduced pressure, which is characterized by adjusting the degree of vacuum of a vacuum ladle degassing device, and an apparatus for carrying out this method. [Example 1] Hereinafter, the method of the present invention will be described in detail with respect to one embodiment of the apparatus of the present invention for carrying out the method of refining molten steel under reduced pressure according to the present invention. The drawing is a block explanatory diagram of one embodiment of the apparatus for refining molten steel under reduced pressure according to the present invention. In the figure, 1 is a vacuum vessel, 2 is a steel stock installed in the vacuum vessel 1, and into which molten steel 3 to be refined is poured;
4 is a porous plug for blowing inert gas such as argon gas into the molten steel 3 from the bottom of the ladle 12 installed in the vacuum container 1; 5 is a porous plug in the ladle 2 installed in the vacuum container 1; Melt! ! 43 is an oxygen lance for supplying oxygen to the upper surface; 6 is an exhaust gas line connected to the vacuum vessel 1 to reduce the pressure inside the vacuum vessel 1; and a vacuum pump or steam A pressure reducing means 7 such as an ejector is connected. Reference numeral 8 denotes a vacuum gauge for measuring the pressure in the exhaust gas passage 6, and numeral 9 denotes a gas analyzer for analyzing the gas in the exhaust gas passage 6. This gas analyzer 9 was first developed by the applicant in Japanese Unexamined Patent Publication No. 59-185720.
The gas analyzer used in the method illustrated in this issue may be used. Reference numeral 10 is a vacuum degree pattern setting device for setting the temporal pressure change in the vacuum vessel 1 as a vacuum degree pattern in accordance with the steel type of molten steel, and 11 is a vacuum degree pattern setting device that sets the temporal change rate pattern of the decarburization rate of the molten steel 3 in accordance with the steel type of molten steel. A decarburization rate over time change rate pattern setter 12 is a decarburization rate over time change rate pattern set in advance as a decarburization rate over time change rate pattern. The proportional integrator 12 is a proportional integrator that proportionally integrates only the positive value of the value obtained by subtracting the pressure, and the processed signal of the proportional integrator 12 is outputted to the adder 13. 14 is a decarburization rate over time change rate pattern of the molten steel 3 preset in the decarburization rate over time change rate pattern setter 11 from the rate of change over time of the decarburization rate determined by gas analysis by the gas analyzer 9 in the exhaust gas path 6. This is a proportional-integral-differentiator that performs proportional-integral-differential differentiation of only positive values among the subtracted values, and the processed signal of this proportional-integral-differentiator 14 is also output to the adder 13. Reference numeral 15 is installed in an air inlet pipe connected to the gas discharge side of the exhaust gas path 6, which is remote from the vacuum level gauge 8 and the gas analyzer 9, in order to adjust the degree of vacuum of the pressure reducing means 7 based on the signal from the adder 13. It is a chounaben that is
Instead of the regulating valve 15, the degree of vacuum may be adjusted by the pressure reducing means 7 itself, such as a vacuum pump or a steam ejector, using a signal from the adder 13. [Function] In order to carry out the method of the present invention using the apparatus for refining molten steel under reduced pressure according to the present invention as described above, first, the oxygen lance 5 and the exhaust gas passage 6 are attached to the bottom of the vacuum vessel 1. A ladle 2 with a porous plug 4 attached and injected with molten steel 3 to be refined is installed.At this time, an inner lid (not shown) may be installed on the top of the ladle 2 if necessary. By turning on the operation switch (not shown) that activates the device, inert gas such as argon gas is blown out from the porous plug 4 to stir the molten steel 3, and oxygen is supplied to the top surface of the molten JI43 from the oxygen lance 5 at the top. The molten steel 3 is refined by blowing and maintaining the inside of the vacuum vessel 1 under reduced pressure by the decompression means 7 through the exhaust gas line 6 connected to the vacuum vessel 1.
At the same time, the CO gas and Co2 gas concentrations in the exhaust gas line 6 connected to the vacuum container 1 are analyzed by the gas analyzer 9, and the vacuum set in the preset vacuum pattern setting device 10 is determined. A decarburization rate temporal change rate pattern setting device 11 uses a processed signal obtained by processing a positive value obtained by subtracting the measured pressure from the degree pattern by a proportional integrator 12 and a decarburization rate temporal change rate determined by the gas analyzer 9. The adder 13 adds the positive value obtained by subtracting the decarburization rate aging rate pattern set in advance to the processed signal processed by the proportional-integral-differentiator 14. The degree of vacuum of the pressure reducing means 7 is adjusted so that the larger the value of , the higher the pressure inside the vacuum container 1. The reason why only the positive value when the pressure measured by the vacuum needle 8 is subtracted from the vacuum pattern set in advance in the vacuum pattern setting device 10 is processed is as follows. If the degree of vacuum inside the vacuum chamber advances beyond the preset vacuum degree pattern, the CO reaction will occur in an amount greater than the saturation amount corresponding to the pressure inside the vacuum chamber 1, and bumping phenomena due to Co boiling etc. will easily occur. This is because the degree of vacuum is always kept thicker than the preset vacuum degree pattern, and the decarburization rate over time change rate pattern setting 311 is set in advance based on the rate of change over time of the decarburization rate determined by the gas analyzer 9. The reason why only positive values are processed when the rate of change over time of the decarburization rate is subtracted is that if the rate of change over time of the decarburization rate is slower than the preset rate of change over time of the decarburization rate, the CO reaction in the molten 113 becomes active. This is because the bumping phenomenon is likely to occur due to Co boiling, etc., and the reason why the sum of processed signals with positive values for both the degree of vacuum and the rate of change over time of the decarburization rate is used is that if preset A processed signal of the value obtained by subtracting the measured pressure from the vacuum degree pattern and a processed signal of the value obtained by subtracting the preset rate of change over time of the decarburization rate from the rate of change of the decarburization rate determined by gas analysis. This is to eliminate the possibility that if one is positive and the other is negative, the sum value will be zero or negative and the degree of vacuum of the vacuum ladle degassing device may not be adjusted and a bumping phenomenon will occur. be. Further, the reason why the processed signal related to the degree of vacuum is the signal processed by the proportional integrator 12 and the processed signal related to the rate of change over time of the decarburization rate is the signal processed by the proportional integral differential 314 is that the pressure in the vacuum vessel 1 is set in advance. The effect of being different from the vacuum degree pattern is that the more the rate of change over time of the decarburization rate of molten steel 3 differs from the rate of change over time of the decarburization rate set in advance, the more likely the bumping phenomenon will occur due to Co boiling etc. In order not to affect Co boiling, a processed signal related to the rate of change over time of the decarburization rate, which tends to affect Co boiling, etc., is processed by a proportional integral differentiator 14 with a fast response, which is a proportional integrator and a differentiator. This is because the processed signal related to the degree of vacuum, which does not easily affect the air pressure, etc., is processed by the proportional integrator 12, which has a slow response. [Effects of the Invention] As described above, the method for refining molten steel under reduced pressure according to the present invention, when refining molten steel using a vacuum ladle degassing device,
The pressure of the exhaust gas path connected to the vacuum vessel is measured and gas analyzed, and the positive value processed signal obtained by subtracting the measured pressure from the preset vacuum degree pattern and the change over time in the decarburization rate determined by gas analysis. The degree of vacuum of the vacuum ladle degassing device is adjusted in accordance with the sum of a positive value of a processing signal obtained by subtracting a preset rate of change over time of the decarburization rate from the decarburization rate. method, the vacuum number tl
When refining molten steel using an AM gas device, the pressure inside the vacuum container may differ from the preset vacuum pattern and become more vacuum, making it easier for Co boiling to occur, or the rate of change over time in the decarburization rate of molten steel. When the decarburization rate becomes larger than the preset pattern of change over time, decarburization becomes slow and Co
When boiling, etc. is likely to occur, the degree of vacuum of the vacuum ladle degassing device is adjusted according to the difference from each preset pattern, and the rapid CO, CO, and reactions are suppressed, resulting in bumping of molten steel due to Co boiling, etc. Since the occurrence of this phenomenon can be completely prevented, it is possible to safely and stably refining molten steel using a vacuum ladle degassing device with a larger amount of molten steel injected into the steel ladle than before, and it is also possible to refining molten steel safely and stably using oxygen gas. This is an innovative method that enables blowing and shortens the degassing treatment time, and also reduces the number of repairs in the vacuum container and improves operability. The apparatus for refining molten steel under reduced pressure according to the present invention is an apparatus for carrying out the method for refining molten steel under reduced pressure according to the present invention, which achieves the above-mentioned effects, and achieves the above-mentioned effects with relatively simple equipment. The method of refining molten steel under reduced pressure according to the present invention can be carried out, and iron! ! 4 The industrial l1fl] value in the field of manufacturing industry is always large.

[Brief explanation of drawings]

The drawing shows a sample of the solution R4 under reduced pressure according to the present invention. It is a block explanatory diagram of one example of a funeral. 1. Vacuum vessel 2. Steel stock 3. Molten steel 4. Porous plug 5. Oxygen lance 6. Exhaust gas path 7. Decompression means 8. Vacuum degree needle 9. Gas analyzer 10. Vacuum. Degree pattern setting temperature 11...Decarburization speed red time change rate pattern setter 12...Proportional integrator 13...Additional unit 14...Proportional integral differentiator 15...Control valve

Claims (1)

[Scope of Claims] 1. When refining molten steel using a vacuum ladle degassing device, the pressure of the exhaust gas path connected to the vacuum container is measured and gas analyzed, and the measured pressure is subtracted from a preset degree of vacuum pattern. The value of the sum of the positive value of the processed signal obtained by subtracting the preset decarburization rate pattern over time from the decarburization rate obtained by gas analysis. A method for refining molten steel under reduced pressure, characterized by adjusting the degree of vacuum of a vacuum ladle degassing device in accordance with the above. 2. The method for refining molten steel under reduced pressure according to claim 1, wherein the degree of vacuum of the vacuum ladle degassing device is adjusted by introducing air into an exhaust gas path connected to a vacuum container. 3. The method for refining molten steel under reduced pressure according to claim 1, wherein the degree of vacuum of the vacuum ladle degassing device is adjusted by adjusting the suction force of a vacuum pump connected to a vacuum container. 4. The method for refining molten steel under reduced pressure according to claim 1, wherein the degree of vacuum of the vacuum ladle degassing device is adjusted by a steam ejector connected to an exhaust gas path connected to a vacuum vessel. 5 A vacuum gauge (8) and a gas analyzer (9) for measuring the pressure and gas analysis of the exhaust gas path (6) connected to the vacuum container (1) of the vacuum ladle degassing device, respectively, and the vacuum container ( 1) A vacuum degree pattern setting device (10) that presets the pressure change over time as a vacuum degree pattern; and a molten steel (3).
The rate of change over time of the decarburization rate is set in advance as a rate of change over time pattern of the decarburization rate from the decarburization rate over time change rate pattern setter (11) and the degree of vacuum pattern set in the degree of vacuum pattern setter (10). A proportional integrator (1) that proportionally integrates only the positive value obtained by subtracting the measured pressure in the exhaust gas path (6) measured by the vacuum gauge (8) and outputs it as a processed signal.
2) and the exhaust gas path (6) measured by the gas analyzer (9).
) is processed by proportional-integral-differentiating only the positive value when the decarburization rate temporal change rate pattern set in advance in the decarburization rate temporal change rate pattern setter (11) is subtracted from the decarburization rate temporal change rate. Proportional integral differentiator (14) that outputs as a signal
and an adder (13) that adds the processed signal from the proportional integrator (12) and the processed signal from the proportional integral differentiator (14) and outputs a signal for adjusting the degree of vacuum of the vacuum degassing device. An apparatus for refining molten steel under reduced pressure.