JP7307319B2 - Method for preventing outflow of slag in converter - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for preventing outflow of slag in a converter.

In converter refining, molten pig iron or pretreated molten iron is charged into the converter, and oxygen gas is supplied using top blowing lance or bottom blowing together to perform oxidative refining, decarburization, dephosphorization. Or you can refine both. After refining is completed, molten slag is formed together with molten iron (molten steel) that has finished refining in the converter, and the molten slag floats above the molten iron. The smelting is oxidative smelting, and the molten slag is highly oxidizing (rich in iron oxide) slag. Further, when dephosphorization refining is performed, the phosphorus content in the molten slag increases as a result of the dephosphorization refining.

A tap hole is provided in the side surface of the converter. It is mainly for discharging the molten steel after refining is completed. It is usually called tap hole. After the completion of refining, the molten iron is discharged into the lower ladle through the tapping holes by tilting the converter (hereinafter referred to as "discharging"). It is usually called tapping. At the end of tapping, when the amount of molten iron in the converter decreases, the molten slag formed on the molten iron layer is caught in the molten iron and discharged into the ladle together with the molten iron. As described above, the molten slag in the converter is highly oxidizing and contains a high concentration of phosphorus, which is a harmful impurity. Therefore, if a large amount of molten slag flows into the ladle, the cleanliness of the steel is impaired due to the high oxidizability of the slag. .

A slag cut ball is used as a representative technique for preventing slag from flowing out when hot water is discharged from a converter. The slag cut ball has a diameter larger than that of the tapping hole, and has an intermediate specific gravity between slag and molten iron, and plugs the tapping hole with the slag cut ball at the time when the molten iron finishes coming out and the molten slag begins to come out ( See Non-Patent Document 1). As described in Patent Document 1, in order to achieve this purpose, it is necessary to set the ball-throwing-in position almost directly above the tapping hole, and to throw the ball in the final stage of tapping.

When the slag-cut balls are used, there is a problem that the tap hole is not closed because the floating position of the balls on the surface of the molten metal in the converter is not constant. Slug darts have been proposed to solve this problem. A slug dart has a head and a leg connected thereto, as described in Patent Document 2. During tapping, the foot portion receives the flow of molten steel, and the entire slag dart is drawn to the tapping port of the converter and waits above the tapping port. In this way, it became possible to stably close the outlet.

When using the slag darts, as described in Patent Document 3, the cart holding the slag darts at the tip of the arm is run in the same direction on the rail extending linearly and brought into the converter, and the carriage is brought into the converter. A slag dart is inserted into the tapping hole of the converter at the end of tapping. Rails are provided on the ceiling of the front part of the converter.

Patent Document 4 discloses a method of charging 1 to 5 kg/ton of light-burnt dolomite or quicklime into the upper part of the tapping hole of a tilted converter for tapping, as a method of preventing slag mixed flow in converter dephosphorization. there is It is said that the slag is solidified by locally increasing the basicity only in the tap hole during tapping and its surroundings.

In Patent Document 5, plastic is added to slag on molten steel, the plastic is decomposed by the heat of the slag, and the slag is cooled using the endothermic reaction during plastic decomposition to solidify the slag or cause the slag to flow out. A method of preventing slag outflow is disclosed which increases the viscosity of the slag in an impeded manner. If the amount of plastic added is small, the amount of heat absorbed by the slag is small, and the delay in supplying the oxygen source required for combustion is also reduced, hindering the solidification of the slag. Therefore, the amount of plastic to be added is preferably 1 kg or more per ton of molten steel.

When the slag cut balls and slag darts are not used, and when the slag solidifying materials of Patent Documents 4 and 5 are added, visually confirm that the outflow from the tap hole changes from molten iron to molten slag at the end of tapping, The outflow of slag is stopped by immediately tilting the converter and returning it to the original upright position.

Japanese Utility Model Publication No. 2-48416 JP-A-2000-160225 JP-A-2003-96513 JP-A-3-236413 Japanese Patent Application Laid-Open No. 2006-152370

Iron and Steel Handbook, 3rd Edition II Ironmaking and Steelmaking, pp. 478-479

Of the methods for preventing slag outflow when hot water is discharged from a converter, if the slag darts are used, as described in Patent Document 3, a rail is provided on the ceiling of the converter building and the slag darts are placed in the converter. It is necessary to induce In a converter, especially a small converter, there may not be enough space in the converter building to install such a device for introducing slag darts. On the other hand, when slag-cut balls are used, as described above, the positions at which the balls float on the surface of the molten metal in the converter are not constant, so there is the problem of unstable closing of the tap holes.

In the above-mentioned method of adding a slag solidifying material such as plastic to the slag on molten steel to solidify the slag, a large amount of solidifying material of 1 to 10 kg/t is required, and there is a problem that the input equipment becomes large.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for preventing slag from flowing out of a converter, which can reliably prevent slag from flowing out when hot water is discharged from the converter even in a converter in which a slag dart charging device cannot be installed.

That is, the gist of the present invention is as follows.
[1] A method for preventing outflow of slag in a converter when removing molten iron from a tapping hole of the converter, comprising:
A method for preventing outflow of slag in a converter, characterized in that an oxide fiber having a melting point of 1500° C. or higher is introduced onto the surface of molten slag in a converter during tapping.
[2] The method for preventing outflow of slag in a converter according to Claim 1, wherein the oxide fiber having a melting point of 1500°C or higher is put on the surface of the molten slag in the converter together with a slag cut plug.

The present invention prevents outflow of slag in a converter by throwing oxide fibers having a melting point of 1500° C. or higher onto the surface of the molten slag in the converter when taking out molten iron from a tapping hole of the converter. be able to.

The present inventor focused on adding a fibrous solidification material as a method for preventing slag outflow by reducing the fluidity of slag when hot water is discharged from a converter. That is, in general, when solid phase particles are suspended in slag, the apparent viscosity increases (fluidity decreases). This is because the slag is constrained between the fibers after the mixed fibers are mixed with the slag, so that the flow of the slag can be suppressed with a smaller addition amount. A fiber is defined here as a particle having an aspect ratio (length/diameter) of 100 or more.

As for the material of the fiber, it is necessary that the fiber does not melt due to heat transfer from the slag when the molten steel is discharged from the converter and does not react with the slag or molten steel. Examples of oxides used as materials for such oxide fibers include alumina (Al ₂ O ₃ ) (melting point: 2072° C.) and mullite (3Al ₂ O ₃ .2SiO ₂ -2Al ₂ O ₃ .SiO ₂ ) (melting point: 2072° C.). 1850° C.), zirconia (ZrO ₂ ) (melting point: 2715° C.), and quartz (SiO ₂ ) (melting point: 1650° C.).

Although the length and diameter of the fibers are not limited, the higher the aspect ratio of the fibers, the more easily the fibers are entangled with each other, so the aspect ratio is preferably as high as possible.

The above oxide fiber can be effective even if it is put in alone. effect is obtained. Hereinafter, a locking device including slag cut balls and slag darts, which is put into the converter during tapping, floats in the molten metal, and prevents slag from flowing out at the end of tapping, is collectively referred to as a "slag cut plug". .

Therefore, a 100-ton converter was actually used, and oxide fibers were put into the molten slag in the converter at the time of tapping from the converter to confirm whether or not the slag cutting effect could be obtained. Chopped fiber (short fibers) alumina oxide fibers having a diameter of 5 μm to 30 μm and a length of 3 mm to 100 mm were used as the oxide fibers.

When the molten slag was tapped from the converter, the oxide fibers were added to the surface of the molten slag directly above the tap hole in the converter. rice field. The wettability between the charged oxide fibers and the molten slag was good, and it can be assumed that the oxide fibers were mixed in the molten slag in a short period of time.
The molten slag flow was visually observed during the tapping process, and when molten slag outflow was confirmed, the converter was tilted to stop the slag outflow.

When the amount of oxide fiber added was in the range of 0.05 to 0.5 kg / ton, and the relationship with the amount of slag that flowed into the ladle was evaluated, the amount of slag that flowed out of the ladle was higher than that when oxide fiber was not added. It became clear that the amount of slag flowing out of the ladle decreased as the amount of oxide fiber added increased. The fibers of the added oxide fibers are entangled with each other, and after the oxide fibers added to the molten slag are mixed with the slag, the slag is restrained between the fibers, so that the slag flow can be suppressed with a smaller amount added. It is considered to be

In addition, using the same converter, slag cut balls and oxide fibers were added to the molten slag in the converter when the molten slag was discharged from the converter, and it was confirmed whether the effect of adding oxide fibers could be obtained. rice field. The type and amount of oxide fiber added were the same as above. By closing the tapping hole with the slag cut ball at the timing when the molten material flowing out from the tapping hole changes from molten steel to molten slag, the amount of molten slag flowing out to the ladle can be reduced. When the relationship between the amount of oxide fiber input and the amount of slag that flowed into the ladle was evaluated, the amount of slag that flowed out of the ladle was reduced compared to the case where oxide fiber was not added, and the amount of oxide fiber added was large. Indeed, it became clear that the amount of ladle outflow slag decreased. That is, even when the slag-cut balls and the oxide fibers were used in combination, the effect of adding the oxide fibers was confirmed.

As described above, the outflow of molten slag can be effectively reduced by putting the oxide fiber having a melting point of 1500° C. or higher onto the surface of the molten slag in the converter together with the slag cut balls. If the converter is capable of using slag darts, oxide fibers having a melting point of 1500° C. or higher may be put on the surface of the molten slag in the converter together with the slag darts.

100 tons of hot metal was decarburized and blown in a converter that was used 1500 times or more. The molten slag after blowing had a basicity (CaO/ _SiO2 ) of 3.5, a capacity of 71 kg/ton of molten steel, and a molten steel temperature of 1650°C. After that, the furnace body was tilted to start tapping.

In [Example 1], chopped (short) oxide fibers having a diameter of 5 μm to 30 μm and a length of 3 mm to 100 mm were charged from a chute toward molten slag in a liquid state. In [Example 2], the same oxide fibers and slag cut balls as in Example 1 were charged from a chute toward the molten slag in the liquid state.

In both Example 1 and Example 2, it took about 2 minutes from the time the oxide fibers (and the slag cut balls) were put into the converter until the tapping was completed. For comparison, the operation was also carried out under the condition of not adding oxide fiber or under the condition of adding quicklime particles having an average particle size of 5 mm.

In this operation, the outflow amount of molten slag was calculated by the following method. That is, the thickness of the slag in the ladle was measured with a ruler, and the outflow amount of molten slag was calculated by multiplying the cross-sectional area of the ladle and the density of the slag. Further, the calculated outflow amount was divided by the molten steel amount to obtain the molten slag outflow amount per ton of molten steel. Furthermore, the test was conducted 100 times for each period, and the average value of the outflow of molten slag in each period was obtained.

[Example 1] (insert oxide fiber)
Table 1 shows the types and amounts of oxide fibers used and the resulting molten slag outflow. As a comparative example, test no. In 1, a large amount of slag of 6.0 kg/t flowed out. Test no. In 2 to 4, the amount of slag outflow decreased as the amount of quicklime particles added increased, but a large amount of input was required. Test No., which is an example of the present invention. In Nos. 5 to 16, the amount of slag outflow decreased with the addition of oxide fiber with a smaller amount of input than quicklime particles.

[Example 2] (Adding oxide fibers and slag cut balls)
As slag cut balls added together with oxide fibers, the main composition in mass % is _{Cr2O3 :} 40%, _{Fe2O3 :} 25%, MgO: 10%, _SiO2 : 10%, _{Al2O3 .} : 10%, remainder: refractory which is an impurity was used, and a slag cut ball with a diameter of 220 mm and a weight of 26 kg was used, which was equipped with an iron core inside. The slag cut ball has a specific gravity intermediate between that of molten steel and that of molten slag.

Table 2 shows the types and amounts of oxide fibers used and the resulting molten slag outflow. Test No., which is a comparative example in which neither oxide fibers nor slag cut balls are added. In 1, a large amount of slag of 6.0 kg/t flowed out. Test No., which is a comparative example in which only slag cut balls were thrown. In No. 2, the slag outflow rate was reduced to 4.0 kg/t. Test No., which is an example of the present invention. In 3 to 14, the amount of slag outflow is further reduced by adding oxide fibers in addition to slag cut balls.

Claims (2)

A method for preventing outflow of slag in a converter when removing molten iron from a tapping hole of the converter, comprising:
A method for preventing outflow of slag in a converter, characterized in that an oxide fiber having a melting point of 1500° C. or higher is introduced onto the surface of molten slag in a converter during tapping. 2. The method for preventing outflow of slag in a converter according to claim 1, wherein the oxide fibers having a melting point of 1500[deg.] C. or higher are put on the surface of the molten slag in the converter together with a slag cut plug.