JP3988407B2 - Method for detecting abnormality in vacuum degree in vacuum degassing and method for improving internal quality of thick plate - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a method for detecting an abnormality in the vacuum degree of a vacuum chamber and determining the cause when controlling the degree of vacuum in the vacuum vessel in the vacuum degassing treatment of molten metal, and a thick plate using this method. This is related to the internal quality improvement method.
[0002]
[Prior art]
Vacuum degassing is performed for the purpose of cleaning the molten metal and adjusting the components. For example, in order to vacuum degas the molten steel, either the RH vacuum degassing method or the DH vacuum degassing method is often applied. In the vacuum degassing process, in the case of the RH type shown in FIG. 1, two dip tubes 3 a and 3 b provided in the lower part of the vacuum chamber 3 disposed above the container 2 containing the molten steel 1 are provided. Then, the molten steel 1 is circulated and introduced into contact with the vacuum atmosphere in the vacuum chamber 3 to remove gas and impurity elements. Further, an exhaust system 5 continuing from the exhaust duct 4 is connected to the vacuum chamber 3, and exhaust for maintaining the inside of the vacuum chamber 3 at a predetermined degree of vacuum is performed.
[0003]
Moreover, in FIG. 1, the code | symbol 6 is an oxygen gas blowing lance, the code | symbol 7 is an alloy iron shooter, the code | symbol 8 is a pressure gauge, and the code | symbol 9 is an adhesion | attachment metal.
In the DH type vacuum degassing method, the molten steel is pulled up by a single dip tube, but the basics of exposing the molten steel to a vacuum atmosphere are the same as in the RH type vacuum degassing method.
[0004]
In such a vacuum degassing process, it is indispensable to maintain the inside of the vacuum chamber 3 at a predetermined degree of vacuum. Therefore, the degree of vacuum inside the vacuum chamber 3 is monitored and set so as not to deviate from that set. It is important to control. Therefore, a part of the atmosphere in the vacuum chamber 3 is guided to a pressure gauge 8 provided in the exhaust duct 4 to measure the pressure, and the degree of vacuum in the vacuum chamber 3 is managed based on the measurement result.
[0005]
Japanese Patent Laid-Open No. 8-170116 discloses that a vacuum gauge is installed in each of a vacuum generator system connected to a vacuum chamber, and a dust separator system and an alloy addition system following the vacuum generator system. It is disclosed that the measured value according to the above is compared with the degree of vacuum set according to the operation pattern of the vacuum degassing process, and the leaked part causing the abnormality in the degree of vacuum is identified by the comparison result. Yes.
[0006]
However, in any case, since the degree of vacuum is measured outside the vacuum chamber 3, such as an exhaust system after the exhaust duct 4 of the vacuum chamber 3 or an alloy addition system (alloy iron shooter), it is in direct contact with the molten steel. There was a problem that it was difficult to accurately detect fluctuations in the degree of vacuum in the vacuum chamber.
[0007]
That is, the value of the degree of vacuum measured in the exhaust system outside the vacuum chamber is effective for detecting pressure fluctuations caused by leakage in the system. For example, in the exhaust system shown in FIG. In the case where the molten steel in the vacuum chamber 3 flies to the entrance side (vacuum chamber side) of the exhaust duct 4, which is a connection place with the air duct 3, and solidifies as it is to become a deposit 9. Accurate detection of the degree of vacuum becomes impossible. This is because the adhering material 9 obstructs the passage of the exhaust gas guided from the vacuum chamber 3 to the exhaust system, so that the vacuum level in the exhaust system does not vary so much while the vacuum level in the vacuum chamber decreases rapidly. Because it becomes.
Therefore, as a result of the difference between the degree of vacuum in the exhaust system and the degree of vacuum in the actual vacuum chamber, it becomes impossible to accurately control the degree of vacuum in the vacuum chamber.
[0008]
In the above-described prior art, a vacuum meter is provided for each system, so that the maintenance load is also a problem.
[0009]
[Problems to be solved by the invention]
Therefore, in controlling the degree of vacuum in the vacuum chamber, the present invention is not limited to fluctuations in the degree of vacuum in the vacuum chamber due to leakage from a joint represented between the vacuum chamber and the exhaust system. The purpose is to propose a method that can accurately detect the fluctuation in the vacuum degree in the vacuum chamber due to the decrease in the exhaust capacity due to the deposit on the inlet side of the gas and determine which of the fluctuations in the vacuum degree is caused. And
[0010]
Another object of the present invention is to propose a method of using the detection result of the vacuum degree in the vacuum chamber obtained by the above method for suppressing segregation in a product, particularly a thick plate.
[0011]
[Means for Solving the Problems]
The present invention has been made to solve the above-mentioned problems, and the gist thereof is as follows. That is, when vacuum degassing is performed by sucking molten metal into a vacuum chamber whose interior is maintained in vacuum and bringing it into contact with a vacuum atmosphere, exhaust for maintaining the vacuum chamber at a preset pressure. Measure the pressure in the exhaust system continuously, compare the measured pressure with the set pressure, and if the measured pressure exceeds the set pressure, determine that the degree of vacuum is abnormal due to the occurrence of a leak. When the pressure is lower than the set pressure, the pressure in the vacuum chamber is directly measured every several charges, and when the pressure value of the direct measurement exceeds the set pressure value, an abnormality in the degree of vacuum due to clogging of the exhaust system is detected. a vacuum abnormality detection determination method in the vacuum degassing process and judging.
[0012]
The present invention also hit the manufacturing planks molten steel passing through the vacuum degassing as a material, at the time the vacuum abnormality is detected by the vacuum abnormality detection determination method, the molten steel passing through the vacuum degassing process Is a method for improving the internal quality of a thick plate, characterized in that it is determined as a dehydrogenation failure and a dehydrogenation treatment is performed on the thick plate manufactured from the molten steel.
[0013]
Here, the determination of the dehydrogenation failure is preferably performed over all charges that have undergone the vacuum degassing process at the time when the degree of vacuum is abnormal, in order to improve the internal quality of the thick plate.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Next, the vacuum degree abnormality detection determination method in the vacuum degassing process of the present invention will be described in detail with reference to FIG.
First, as in the vacuum degassing process shown in FIG. 1, a part of the atmosphere in the vacuum chamber 3 is led to a pressure gauge 8 provided in the exhaust duct 4 to perform pressure measurement periodically, for example, for each charge. If the measured value (measured pressure) with the pressure gauge 8 exceeds the vacuum degree in the vacuum chamber set for each operation (hereinafter simply referred to as “set value”), the vacuum degree is abnormal in the vacuum chamber. Is determined to have occurred. In this case, since both the pressure in the vacuum chamber 3 and the exhaust duct 4 have increased, it can be determined that a leak has occurred in the exhaust system after the exhaust duct 4.
[0015]
On the other hand, when the value of the pressure measured by the pressure gauge 8 is equal to or lower than the set value, it can be assumed that the degree of vacuum in the vacuum chamber 3 is maintained within a predetermined range. 1 to 5 to 10 charges, for example, a vacuum gauge is inserted into the tank through a gas sampling probe (not shown) from the probe insertion port 10 shown in FIG. Measure directly. When the measured pressure value obtained by this direct measurement (hereinafter simply referred to as “measured value”) exceeds the set value, the measured value by the pressure gauge 8 is less than the set value, and the leak in the exhaust system Therefore, it can be determined that the deposit 9 is generated between the vacuum chamber and the exhaust duct, and therefore, it is determined that the exhaust system is clogged.
[0016]
As described above, an abnormality in the degree of vacuum can be detected and the cause of the abnormality can be determined. Therefore, it is possible to easily and reliably carry out equipment inspection and repair based on the obtained information.
[0017]
By the way, although various gases and impurity elements are removed in the vacuum degassing process, hydrogen inevitably mixed is also removed by the vacuum degassing process. If this hydrogen is not sufficiently reduced at the steelmaking stage, segregation in the vicinity of the center of the thickness of the product, particularly a thick plate product, results in a defective product, so it is necessary to suppress this hydrogen within a predetermined range. Conventionally, if the amount of hydrogen in the sample is within an acceptable range according to the analysis of the sample taken from the molten steel, all of the charged molten steel is sent to the rolling process.
[0018]
However, in general, in the sample analysis, as shown in FIG. 3, the hydrogen amount deviates from the allowable range due to the change in the operation condition even within the same charge, as can be seen from the fact that the change greatly depends on the cooling condition after collection. There is a case. For example, as shown in FIG. 4, there is a particularly strong correlation between the hydrogen analysis value of the sample and the occurrence of defects due to hydrogen segregation in the product for the various thickness plates manufactured from the same charged molten steel. Not necessarily. Therefore, it has been difficult to predict and prevent the occurrence of defects due to hydrogen segregation based on hydrogen analysis using samples.
[0019]
Here, the inventors have intensively studied, and the amount of hydrogen in the molten steel correlates well with the degree of vacuum in the vacuum degassing process, and the amount of hydrogen does not increase unless the degree of vacuum deviates from the set value. In other words, it has been found that the amount of hydrogen increases when the degree of vacuum varies.
[0020]
Accordingly, since the fluctuation of the vacuum degree is grasped by using the above-described detection and determination method of the abnormality in the vacuum degree, the hydrogen content is increased based on this for the operation in which the abnormality in the vacuum degree has occurred. Under the premise, it was possible to avoid the occurrence of defects due to segregation in the product by dehydrogenating the product manufactured from the molten steel at the charge.
[0021]
That is, at the time when an abnormality in the degree of vacuum is detected by the method for detecting abnormality in the degree of vacuum, the molten steel that has undergone the vacuum degassing process is determined to be dehydrogenated, and a dehydrogenation process is performed on the thick plate manufactured from the molten steel; did. As this dehydrogenation treatment, so-called dehydrogenation annealing may be performed, and a method of performing a slow cooling treatment on a product or the like may be advantageously employed. In the case of detecting the degree of vacuum abnormalities, including molten steel passing through the vacuum degassing treatment at the time sensed by the last vacuum abnormality detection determination was performed in the vacuum degassing process after the time it is determined that no abnormality All products manufactured from molten steel shall be dehydrogenated to guarantee all products.
[0022]
It is effective to reduce the occurrence rate of defects due to segregation in the product by determining the dehydrogenation failure over all the charges that have been subjected to the vacuum degassing process when the degree of vacuum is abnormal.
[0023]
【Example】
Comparative Example In the vacuum degassing treatment of molten steel performed at a high vacuum of 150 Pa or less, as shown in FIG. 1, the pressure in the pressure gauge 8 is measured, and the vacuum in the vacuum chamber is determined to be within the set value. A thick plate (40 mm thick) was produced only from the molten steel. As a result, the incidence of area segregation failure occurring at 1/2 thickness in thick plate products was 0.3%.
[0024]
As in the invention example, in the vacuum degassing treatment of molten steel performed at a high vacuum of 150 Pa or less, the vacuum chamber 4 is connected via the gas sampling probe 10 together with the pressure measurement in the pressure gauge 8 as shown in FIG. Measure the pressure of the gas collected directly from 5 times once in 5 charges, and use a thick plate (40mm thickness) only from the molten steel with the charge determined that the vacuum in the vacuum chamber is within the set value. Manufactured. As a result, there was no occurrence of poor area segregation that occurred at 1/2 thickness in the thick plate product.
[0025]
【The invention's effect】
As described above, according to the present invention, it is possible to detect an abnormality in the degree of vacuum and determine the cause thereof, so that it is possible to easily and reliably carry out equipment inspection and repair based on the obtained information. Is possible. Further, by using the detection result of the vacuum degree in the vacuum chamber obtained by this method for suppressing segregation in the product, it is possible to prevent the occurrence of segregation failure in the product.
[Brief description of the drawings]
FIG. 1 is a view showing a vacuum degassing apparatus.
FIG. 2 is a view showing a vacuum degassing apparatus used in the present invention.
FIG. 3 is a diagram showing changes in sample analysis values depending on cooling conditions.
FIG. 4 is a diagram showing a relationship between sample analysis values and occurrence of segregation failure.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Molten steel 2 Container 3 Vacuum tank 3a, 3b Immersion pipe 4 Exhaust duct 5 Exhaust system 6 Oxygen gas blowing pipe 7 Alloy iron shooter 8 Pressure gauge 9 Deposit 10 Probe insertion port

Claims (3)

In sucking the molten metal into the vacuum chamber and performing vacuum degassing treatment, the pressure in the exhaust system is measured to exhaust the vacuum chamber to maintain the set pressure, and the measured pressure and the set pressure If the measured pressure exceeds the set pressure, it is determined that the degree of vacuum is abnormal due to the occurrence of a leak.On the other hand, if the measured pressure is less than the set pressure, the pressure in the vacuum chamber is directly measured every few charges. and vacuum abnormality detection determination method in the vacuum degassing treatment, characterized in that the pressure value of the direct measurement is determined to vacuum abnormality of the exhaust system clogging at the time of exceeding the set pressure value. When manufacturing a thick plate using molten steel that has been subjected to vacuum degassing as a raw material, it is determined that the molten steel that has undergone vacuum degassing is defective in dehydrogenation when an abnormality in the degree of vacuum is detected by the method according to claim 1. And a method for improving the internal quality of the thick plate, wherein a dehydrogenation treatment is performed on the thick plate manufactured from the molten steel. 3. The method for improving the internal quality of a thick plate according to claim 2, wherein the determination of a dehydrogenation failure is made over all charges that have undergone a vacuum degassing process at a time when the degree of vacuum is abnormal.

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