JPH01180764A - Method for continuously casting high clean steel - Google Patents

Abstract

PURPOSE:To promote floating-up of inclusion by adding the specific concns. of SiO2 and CaO flux on molten steel surface at the time of dipping a rotator arranging blades in a vessel and supplying inert gas between these blades to remove the inclusion by stirring and bubbling. CONSTITUTION:Driving device 2 is laid on a fixed table 1 arranged at upper part of a tundish A and a rotary body 6 arranging the rotator 4 through a casing 3 is connected with the driving device 2. The inert gas is blown into the molten steel 11 from gas blowing part 10 through an inert gas inlet 8 and center shaft 9 for the rotator 4. The rotator 16 is cooled through an intermediate pipe 13 outer wall 15 and cooling air. At the time of floating up to remove the inclusion by stirring and fine bubble of the inert gas, the low SiO2 and high CaO flux containing of <=5% SiO2, 30-98% CaO and molten viscosity adjusting agent of one or more kinds among CaF2, Al2O3 and MgO is added on the molten metal surface. By this method, the inclusion is surely absorbed and re-enclosure and air-oxidation, etc., are prevented and the high purity steel can be obtd.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a method for removing inclusions in molten steel.

Conventional technology Molten steel cast by continuous casting is generally melted in a refining furnace such as a converter ψ electric furnace, then tapped into a ladle, deoxidized, and its composition adjusted. Contains non-metallic inclusions.

During casting, some of these nonmetallic inclusions float and separate in the ladle, tundish, and mold, but most of them float away in the slab and mold.
It is known that it is trapped in slabs such as bloom and solidifies, significantly impairing the quality of steel materials.

As an example of a means to prevent the quality of steel products from being impaired due to the nonmetallic inclusions in the molten steel being trapped in the slab, the nonmetallic inclusions are separated and removed in the tundish during continuous casting. Many methods have also been proposed.

As this separation and removal method, for example, Japanese Patent Application Laid-Open No. 58-884
As shown in Publication No. 58, an air-permeable refractory is buried in the bottom of the tundish, and inert gas is blown in a direction perpendicular to the molten steel flow to remove inclusions.
As shown in Japanese Utility Model Publication No. 58-4847, etc., a gas passage is formed inside the shaft, and a stirring blade or a horizontal surface plate is provided at the tip of the shaft to generate fine bubbles of fluxing gas. Efforts are being made to make the explosion cleaner using devices such as blowing equipment.

However, these conventional methods for removing inclusions cannot be said to be sufficient for the reasons described below.

First of all, the method of blowing gas using a porous plug in a tundish cannot stably supply a uniform supply of fine bubbles. The gas flow and the diameter of the generated bubbles also tend to be non-uniform, and the accompanying strength of agitation may induce entrainment of inclusions on the surface layer. In particular, when floating flux is not used, the porous plug method is not recommended as a method for removing inclusions, not only because of the above-mentioned entrainment, but also because air oxidation of the molten steel becomes noticeable as the molten steel surface becomes bare. It is enough.

On the other hand, in the case of blowing with a rotary blade, since the rotary blade is immersed above the molten steel bath surface of the tundish and rotated, the bath surface vibrates, and conversely floating slag or flux is drawn in or - This causes the inclusions that have floated up to become re-engulfed. In addition, floating slag and flux are pushed away by the shaking of the bath surface, resulting in air oxidation due to bare hot water, leading to an increase in inclusions in the steel.

Furthermore, a method of adding CaO-based flux has been proposed in order to prevent the influence of vibration of the bath surface due to the rotating blades and heat dissipation from the bath surface. However, it has been essential that this flux has a composition that can promote the dissolution of the flux itself in order to keep the tissue warm and absorb floating inclusions. For this reason, even if the above-mentioned floating inclusions are adsorbed, re-entrainment occurs as a result, and this phenomenon is particularly noticeable in the current situation where the continuous casting ratio is high, making it difficult to put it into practical use.

Problems to be Solved by the Invention The present invention solves the drawbacks of the conventional method as described above.
In addition to ensuring the floating of inclusions through uniform and stable microbubbles and agitation of the bath, entrainment of the floating inclusions can be sufficiently suppressed, and moreover, by improving the adsorption ability of floating inclusions over a long period of time, a high The object of the present invention is to provide a continuous casting method capable of obtaining clean steel.

Means for Solving the Problems The present invention involves immersing a rotor with blades in a molten metal container, and supplying an inert gas between the blades to float and remove inclusions by stirring and fine bubbles. In doing so, the surface of the molten metal is coated with SiO2≦5%, CaO30-98%, and C.
low SiO2 containing a melt viscosity modifier consisting of aF2, Al1203, MgO (1) or two types;
This is a continuous casting method for high-clean steel characterized by the addition of high-CaO flux.

This will be explained in detail below.

Function The inventors of the present invention obtained the following knowledge as a result of various studies and experiments on floating and removing inclusions mixed in molten steel in a molten metal container.

(1) First, the floating of inclusions by air bubbles and mechanical agitation is extremely effective in removing inclusions compared to other means due to the coarsening effect caused by promotion of flotation and collision, and furthermore, it is preferable that the air bubbles be made finer.

■Floated inclusions are not necessarily removed, and are re-entrained by the bubble-forming gas blown in or mechanical agitation flow, and if weak agitation is used to prevent this, the inclusions themselves will suddenly become buoyant. decrease.

■While maintaining strong stirring of the bath, which is favorable for the floating of inclusions, and covering the inclusions with a high-viscosity flux and a flux with high absorption capacity, high viscosity and high adsorption can be achieved at the molten interface on the bath surface, which was previously unobtainable. The effect is expressed, etc.

Based on the above-mentioned knowledge, the present invention is based on mechanical stirring of a bath and the floating of inclusions (hereinafter referred to as strong inorganic stirring) by fragmented fine bubbles of inert gas blown between the impellers that induce the stirring. ) while adding a high viscosity flux with a high CaO content and a reduced SiO2 content to the bath surface.

By combining the addition of this low-SiO2, high-CaO content flux and strong inorganic stirring, the flux in the extremely poor floatation range, which cannot be achieved conventionally, can be dissolved in a highly viscous state.
Capable of capturing and adsorbing 03-based inclusions.

Moreover, high adsorption capacity and high viscosity could be maintained for a long period of time during multiple castings.

As described above, the present invention uses inorganic stirring to agglomerate not only large inclusions but also minute inclusions by collision and contact action, and removes them by mechanical stirring flow and the trapping and floating effect of fine bubbles.

On the other hand, this strong stirring causes the bath surface to shake violently. This fluctuation of the bath surface promotes the dissolution of a part of the low 5in2, high CaO flux that covered the surface, and the lower layer of the flux is a highly viscous melt with an extremely high ability to adsorb Ab and other inclusions. form a layer. The molten layer of flux formed on the bath surface quickly adsorbs inclusions that float up due to the vibration of the bath surface, even though they have high viscosity. Moreover, since it is captured and held within the high-viscosity molten layer, it will not be drawn into the bath by the turbulence of the bath surface.

In addition, since a very small amount of flux is sequentially dissolved by inorganic stirring to form a molten layer, the adsorption source of A(1203-based inclusions) is constantly stabilized at a high level, and a molten layer in a highly viscous state can be maintained for a long period of time.

The content of SiO2 as this high viscosity flux is 5% or less to prevent the viscosity from becoming low due to the reaction with ^92o3 in floating inclusions and AQ and 03 minutes due to melting of the refractory, and also to prevent the viscosity from decreasing due to the reaction with A9 in the steel. This prevents the formation of Au203 due to the reaction. When the SiO2 content exceeds 5%, the viscosity decreases rapidly due to the above reaction, and floating inclusions are re-engulfed by stirring. Furthermore, by contacting with steel medium M, A1. is oxidized to Aq
203 and contaminates the molten steel.

In addition, although the surface of the M bath is covered with flux to suppress air oxidation, the coating layer is locally peeled off due to agitation due to promotion of slag formation and low viscosity during the PI manufacturing period, and the coating effect is inhibited. For this reason, by setting the SiO2fl content to 5% or less, extremely stable adsorption, increased viscosity as the melting point rises, prevention of molten steel contamination, and bath surface coating effects can be obtained.

Next, in order to increase the CaO content, add 30 to 30% CaO.
It shall be 98%. If the CaO content is less than 30%, problems similar to those described above will occur, and the adsorption ability of Au203 will decrease. In addition, when the CaO content is more than 88%, the dissolution reaction is completely suppressed, and even if inorganic stirring (strong stirring) is performed, a highly viscous flux is not generated, resulting in At
203 adsorption is inhibited.

Also, CaF is dissolved or added as a viscosity modifier.
2 is 0 to 35%. If the amount is more than this, the same problem as mentioned above will occur, and if it is too little, the flux will become sintered. On the other hand, as the wear of refractories increases rapidly as the CaF2 content increases, CaF2≦20%
is more preferable.

Furthermore, as the viscosity modifier added other than these, some At203, MgO, etc. may be included, especially A
t,03 is preferably set to 15% or less since it reduces the adsorption of floating inclusions depending on the amount added.

Furthermore, when used as a low SiO2, high CaO flux, if the flux is made into particles with an average particle size of 0.5 to 10 m, sintering of the flux can be prevented when added to the bath surface, and a highly viscous molten layer can be formed. The formation of is stabilized.

For this reason, when the flux is made into a sphere, its effect becomes more pronounced.As a method for making the flux into a sphere, ordinary means such as pelletizing are used.

EXAMPLE Next, a case will be described in which the method for producing highly clean steel according to the present invention is used in a tundish during continuous casting of molten steel. 1st
The figure shows a cross-sectional view when the high-cleanliness steel manufacturing method according to the present invention is applied to a tongue pusher, and FIG. 2 shows a cross-sectional view taken along line xx' of the blade portion in FIG. 1.

First, a drive device 2 consisting of a combination of a motor and gears, for example, is mounted on a fixed base l built on the upper part of the tandem dish A, and a rotor 4 is attached to the drive device 2 through a casing 3. The bodies 6 are connected.

This rotor 4 is provided with an inert gas port 8 for supplying an inert gas from the outside, and is blown into the molten steel 1 from an inert gas blowing part 10 at the tip of the rotor 4 through the central axis 9 of the rotor 4. It is. This blown gas is finely chopped by the blade portion 17. Further, the rotor 4 is cooled via the inner pipe 13, the outer pipe 15, and the cooling air pipe 12.

This rotor 4 was manufactured under the conditions shown in Table 1, the steel type, and the casting conditions, and also at a low temperature! 9i02, a high CaO flux having the composition and shape shown in Table 2 was used, and a comparative material was tested using only bottom bubbling.

The results are shown in Figure 3, and it is clear that by using the final method, inclusions can be promoted to float, and adsorption and re-entrainment by flux can be suppressed, and as a result, surface defects and internal defects caused by inclusions can be reduced. It can be seen that the quality of the slab has been significantly improved and that so-called high cleanliness has been achieved.

In addition, FIG. 3 is expressed as the total average of the Examples shown in Table-2.

Furthermore, the cleaning method is not limited to tundish dishes, but can also be used to clean ladle in the same manner.

(Leaving space below) Table 1 Table 2 Effects of the invention I: As stated above, by using the manufacturing method of high-clean steel according to the present invention, it is possible to promote the floating of inclusions, ensure their adsorption, and re-entrain them. Furthermore, it is possible to prevent quality deterioration due to air oxidation, etc., and it is possible to obtain highly clean steel. This high level of cleanliness makes it possible to manufacture high-grade steel and improve yields by making the type of melted product defect-free.1
The present invention is an extremely excellent casting method.

[Brief explanation of the drawing]

FIG. 1 shows a sectional view of an example in which the method of the present invention is applied to a tundish dish 2. As shown in FIG. FIG. 2 shows a cross-sectional view along the line xx' of the blade portion in FIG. 1. FIG. 3 is a diagram showing a comparison of internal cracks and surface flaws between the final method and the conventional method. ■... Fixed base, 2... Drive device, 3... Casing, 4... Rotor, 5... Bearing, 6... Rotating body, 7. Fist rotary joint, 8... ... Inert gas inlet, 9 ... Central axis, 10 ... Inert gas blowing part, 11 ... Molten steel, 12 ... Cooling air population, 13
No. 0, middle tube, 14... feather, 15... outer tube, te-
- Φ Rotor body shaft part, 17... Vane part, 1B... Slag line part, 18... Molten water surface, 20-... Flux.

Claims (1)

[Claims] A rotor with blades is immersed in a molten metal container,
In addition, when an inert gas is supplied between the blades to float and remove inclusions by stirring and fine bubbles, SiO_2≦5%, CaO30-98%, and CaF_2 are added to the surface of the molten metal.
, Al_2O_3, low SiO_2, high CaO containing a melt viscosity modifier consisting of one or more types of MgO
A continuous casting method for high-purity steel characterized by the addition of flux.