JPH02285036A - Vacuum refining method for molten metal - Google Patents

Abstract

PURPOSE:To execute vacuum refining of molten metal in a short time by adding solid compound containing gas component to molten metal, reducing the pressure after dissolving gas, generating fine gas bubble in the molten metal and trapping inclusion with this. CONSTITUTION:The gas of N2, etc., which is soluble in molten metal, is dissolved into the molten metal. At the same time of or after dissolving, the pressure is reduced and the fine gas bubbling is generated in the molten metal. The inclusion in the molten metal is trapped with this bubble and removed. In the vacuum refining method of the above molten metal, the solid compound containing the above gas component of e.g. the ferro manganese nitride containing about 6% N, is added to the molten metal to execute the above gas dissolving treatment. As the above adding method, the solid compound is pulverized under pressurizing and by injecting the gas using the soluble gas, etc., the refining can be executed. By this method, the dissolving of gas component is executed in the short time and the efficiency of the above vacuum refining method is improved.

Description

[Detailed description of the invention]

[Industrial Application Field] This invention relates to a vacuum refining method for removing impurities and inclusions in molten metal. [Prior Art] The present inventors have proposed the following in order to improve the efficiency of removing inclusions from molten metal. That is, a gas soluble in the molten metal is dissolved by bubbling, and fine gas bubbles are generated in the molten metal by reducing the pressure. According to this method, even minute inclusions in the molten metal are trapped by the bubbles and floated to the surface, resulting in extremely high inclusion removal ability. On the other hand, the present inventors got a hint from the bubble floating state in the above-mentioned inclusion removal method, and developed the application of this to a degassing refining method and a slag refining method. That is, according to the above procedure, fine gas bubbles are generated in the molten metal,
The floating causes the interface between the molten metal and the atmosphere or the interface between the molten metal and molten slag to flutter, thereby increasing the reaction interface area. Since these gas bubbles are generated from the entire area of the molten metal, the flutter at the interface extends over the entire area of the interface. Moreover, since the gas bubbles are fine and generated in large quantities, the reaction interface area increases significantly, and the ability to remove impurities by degassing refining and slag refining becomes extremely high. [Problems to be solved by the invention] Both refining methods are very efficient methods for removing inclusions and impurities in molten metal and obtaining ultra-clean molten metal. The processing time for dissolving soluble gas by bubbling is long, and the total processing time, including the processing time for removing inclusions and impurities, still requires more than 30 minutes, and there is a desire to further shorten this time and improve efficiency. was there. The present invention was devised in view of the above problems, and aims to improve the gas dissolution process in the vacuum refining method described above, thereby shortening the process time. [Means for solving the problem] Therefore, the present invention provides the above-mentioned method for removing inclusions and
In the impurity removal method, a solid compound containing a gas component soluble in the molten metal is added to the molten metal, thereby performing a gas dissolution treatment. In the conventional gas addition method, which performs gas dissolution treatment by gas bubbling, if we were to add N2 to molten steel in a ladle, the amount of [N] in the molten metal would be increased by 400 ppm, but the normal amount of bubbling would be (At most 0.02N++
+"/+ain4) requires 15 minutes or more. On the other hand, in the method of the present invention, for example, if ferromanganese nitride containing about 6% N is to be added, it is added to the molten metal for 6 minutes.
．． It is only necessary to add 1 kg/TON, and even considering the yield, it is possible to add in a much shorter time than the conventional addition method. By adding the above-mentioned solid compounds under pressure, a large amount of gaseous components will be dissolved, and it will also be possible to prevent what has already been dissolved to become gas again and escape from the molten metal. Also, if the solid compound itself to be added is in powder form, the total surface area of the solid compound that comes into contact with the molten metal will increase, and the melting will be faster. Blow-in is efficient because it melts quickly over the entire area of the molten metal. If a gas soluble in the molten metal is used for injection, the efficiency of the gas dissolution process will be further increased. [Examples] Specific examples of the present invention will be described below. 50TON (7) 6350T melted in V A D equipment
ON was turned on, and 500 kg of powdered ferromanganese nitride was injected into the molten steel using a submerged top blowing lance. At this time, Ar gas is used as the carrier gas, and INm''/win
The injection was completed in about 6 minutes. The (N) content in the molten steel immediately after this injection was completed was 410 ppm. After that, the pressure was rapidly reduced to 1 torr. It was left for 20 minutes. On the other hand, in the same VAD equipment, N2 gas was injected INm''/@i into 507ON molten steel using a submerged top blowing lance.
Bubbling was carried out for 21 minutes. Immediately after this bubbling was completed, the (N) in the molten steel was 4αOppm, which is the same as in the above-mentioned example of the present invention. Then 1tor
The pressure was rapidly reduced to r and left for 20 minutes. The following clothes were used for 20 minutes after the start of decompression when carrying out the above two examples.
(N) and T in molten steel until the elapse of minutes

It shows a change in [0]. As is clear from this table, the ability to remove inclusions in molten steel is 2.
It was almost the same as the example. However, in the example of the present invention, the injection of ferromanganese nitride performed as a gas dissolution treatment was approximately 6
It was possible to shorten the gas dissolution treatment time by about 15 minutes compared to the bubbling time in the latter gas bubbling example. [Effects of the Invention] According to the vacuum refining method of the present invention described in detail above, the gas dissolution treatment time can be shortened, so it has an excellent effect that the refining treatment time can be shortened as a whole.

Claims (6)

[Claims] (1) Dissolving a gas soluble in the molten metal,
In a vacuum refining method for molten metal, in which the pressure is reduced at the same time or after that, fine gas bubbles are generated in the molten metal, and the inclusions in the molten metal are removed by being trapped in the bubbles. A vacuum refining method for molten metal, characterized in that the gas dissolution treatment is performed by adding a compound to the molten metal. (2) Dissolving a gas soluble in the molten metal,
At the same time or after that, the pressure is reduced to generate fine gas bubbles in the molten metal and trap them in the bubbles to remove inclusions in the molten metal. Alternatively, in a vacuum refining method for molten metal in which impurities in the molten metal are removed by flapping the interface between the molten metal and molten slag to increase their respective reaction interface areas, a solid compound containing the above-mentioned gas components is added to the molten metal. A vacuum refining method for molten metal, characterized in that the gas dissolution treatment is performed by adding molten metal to molten metal. (3) In the vacuum refining method for molten metal according to claims 1 and 2, the solid compound is added under pressure. Vacuum refining method for molten metal as described. (4) In the vacuum refining method for molten metal according to claims 1 to 3, the solid compound is added in the form of powder.
Vacuum refining method for molten metal as described in . (5) The vacuum refining method for molten metal according to claim 4, wherein a powdery solid compound is added by injection into the molten metal. (6) In the vacuum refining method for molten metal described in the preceding paragraph, a powdery solid compound is added by injection using a gas soluble in the molten metal. Vacuum refining method for molten metal.