JPH02270909A - How to clean molten metal - Google Patents

Abstract

PURPOSE:To improve removal efficiency of inclusion by adding two or more kinds of deoxidize elements, the deoxidizing strength of which are analogous, in the molten steel at the time of catching and removing the inclusion with gas bubbles by generating fine gas bubbles of dissolved gas under reducing the pressure after dissolving soluble gas into the molten metal of molten steel, etc., containing the inclusion. CONSTITUTION:As gas of O2, H2, etc., and Al2O3 and the other non-metallic inclusion are contained in the molten steel, the gas of N2, etc., is blown with bubbling into the molten steel and dissolved. The N2 gas dissolved, by reducing the pressure of surface atmosphere on the molten steel, is discharged as the fine gas bubbles, and when the gas bubbles rises in the molten steel, the gas of O2, H2, etc., contained in the molten steel is discharged at the same time, and also the non-metallic inclusion of Al2O3, etc., is caught, floated up and removed. When the molten steel is Al-killled steel, by adding the sub-deoxidizing elements of Ca, Mg, etc., the deoxidizing strength of which are analogous, the non-metallic inclusion is made coarsen by flocculating, and the effect of the floating-up and removal is further improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for cleaning molten metal by removing inclusions floating in molten metal.

[Conventional technology]

Inclusions floating in molten metal (for example, alumina inclusions in molten steel) cause product quality defects, and various methods have been proposed to reduce and remove them.

The present inventors have met the requirement that the total amount of oxygen in molten steel should be suppressed to 15 ppm or less for the purpose of manufacturing high-grade materials, and have made the following proposal. That is, the molten metal is bubbled with a soluble gas to dissolve the gas in the molten metal, and then the pressure is rapidly reduced to generate fine gas bubbles in the molten metal. According to this method, normal inclusions in the molten metal are trapped in the gas bubbles and floated to the surface during the initial bubbling. On the other hand, the gas that has melted into the molten metal due to bubbling becomes fine gas bubbles and is generated from the entire area of the molten metal due to the subsequent rapid pressure reduction.

At this time, fine inclusions are trapped by the gas bubbles and float to the surface6.Furthermore, if the gas bubbling is performed on the pressurized molten metal, a large amount of gas will melt into the molten metal. This increases the amount of fine gas bubbles generated after depressurization and increases the inclusion removal rate.Also, if bubbling is performed at atmospheric pressure or lower, fine gas bubbles may be generated during the depressurization process. In addition, the degassing of the molten metal, which is required as a product, is also performed at the same time, so there is no need to degas the bubbling gas that remains in the molten metal in large quantities as a separate processing process. It can increase efficiency. Therefore, the pressure adjustment during bubbling may be appropriately determined depending on the target cleanliness and processing efficiency.

[Problem that the invention seeks to solve]

This is a highly efficient method for removing inclusions in molten metal, and can obtain ultra-clean molten metal in a shorter time than conventional bubbling methods, but the processing time still requires about 10 minutes. There was a request to further shorten this time and improve efficiency.

Also, regarding the final cleanliness level, T・(OF = 5~7
ppm, and compared to the amount of dissolved oxygen in AQ killed steel, it is higher by about 3 to 5 ppm in terms of T [○], and there was a problem that a non-negligible amount of oxygen inclusions remained.

The present invention was devised in view of the above problems, and is intended to improve the efficiency of trapping inclusions by fine gas bubbles.

[Means for solving problems]

Therefore, the basic feature of the present invention is that two or more deoxidizing elements having similar deoxidizing powers are added to the molten metal when carrying out the method for cleaning molten metal described above. .

If this molten metal cleaning method is carried out.

The efficiency with which inclusions are trapped and removed by fine gas bubbles generated in molten metal increases as the diameter of the inclusions increases. Therefore, by coagulating and enlarging the fine oxide-based inclusions generated when the deoxidizing element is added, the trap removal efficiency of the inclusions can be increased.

Based on this idea, the inventors of the present invention have repeatedly investigated various methods for increasing the size of inclusions.

It has been shown that it is effective to add two or more types of deoxidizing elements with similar deoxidizing power to molten metal, so that each of them forms an oxide, and controls the aggregation to form a composite oxide system. I found it. Furthermore, when this method was applied to a method for cleaning molten metal, it was found that it had an outstanding cleaning effect, and the above-mentioned configuration was established as the method of the present invention.

The combination of deoxidizing elements used in the present invention includes AQ
For killed steel, one example is a combination in which Aα is added as a main deoxidizing element and Ca and Mg are added as secondary deoxidizing elements. In the case of AQ killed steel, an example of a combination of Si or Ti as the main deoxidizing element and Mn as the secondary deoxidizing element can be given.

Furthermore, the timing of adding these elements is important.

It has been found that it is sufficient to add these separately or together to the molten metal at least before the start of the reduced pressure treatment.

〔Example〕

650 ton, which will be explained below with specific examples of the present invention.
Put 50 tons of molten steel into the VOD equipment along with the deoxidizer shown below, maintain it at 1660℃ and 650torr,
Apply 6Nm' from the bottom of the ladle for 10 minutes using a porous plug.
, N2 gas was injected. Thereafter, the pressure was rapidly reduced to 1 torr and maintained for 20 minutes. At the same time, Ar gas was bubbled from the bottom of the ladle at 15 ONQ/min.
The molten steel was stirred. At this time, the oxide-based inclusions formed in the molten steel are Ca0AQzO3-based in the method 1 of the present invention, and oxide-based inclusions in the method 2 of the present invention.
A Q, zOa -MgO system, and simple A in the comparative method
Q.It was 03.

＼ As is clear from this table, methods 1 and 2 of the present invention are superior in their ability to remove oxide inclusions, and therefore the reduced pressure required to reduce the inclusions in molten steel to the same level is The standing time for Methods 1 and 2 of the present invention is shorter.

〔Effect of the invention〕

As detailed above, according to the method of the present invention, inclusions are coarsened by adding two or more types of deoxidizing agents with similar deoxidizing power to molten metal, and the inclusions are removed by trapping. Because it can increase efficiency.

When implementing the method for cleaning molten metal, it has the excellent effect of increasing the level of cleaning of the molten metal and shortening the processing time.

Claims (1)

[Claims] The molten metal is bubbled with a soluble gas to dissolve the gas in the molten metal, and then the pressure is rapidly reduced to generate fine gas bubbles in the molten metal to eliminate inclusions floating in the molten metal. When carrying out a molten metal cleaning method in which gas bubbles caused by bubbling and fine gas bubbles generated by depressurization are trapped and removed after floating, two or more types of gas bubbles with similar deoxidizing power are mixed into the molten metal. A method for cleaning molten metal characterized by adding a deoxidizing element.