JP7206923B2 - 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 a converter, and oxygen gas is supplied using a 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 used to discharge molten steel after refining is completed, and is usually called a tapping hole. After the refining is completed, the molten iron is discharged into the lower ladle through the tapping hole 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 tapping 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 legs receive 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 tap hole. When using slag darts, as described in Patent Document 2, a slag holding closure (slag darts) is thrown into the converter at the final stage of tapping from the converter.

Patent Document 3 discloses a branch, a middle stopper attached to the middle of the core bar extending below the branch, and a core bar below the middle stopper at a distance sufficiently longer than the tap hole length. The slag cutting stopper, which has a tapping hole drop-off prevention part attached to the tapping hole of the converter, is coated with a refractory material for the intermediate stopper part, the tapping hole drop-off prevention part, and the core metal that connects them. It is inserted from the inner surface of the converter and adjusted to be lighter than the specific gravity of the molten steel and heavier than the slag at the end of the tapping stage. Thus, a method for preventing slag outflow is disclosed. The slag cut stopper is attached to the tapping hole before pouring hot metal into the converter.

In Patent Document 4, 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 prevent the slag from flowing out. A method of preventing slag outflow is disclosed which increases the viscosity of the slag in an impeded manner.

Patent Document 5 discloses a clogging material charging device for preventing slag outflow during molten metal processing, for charging stopper balls (slag cut balls) into a furnace using a charging chute.

When the slag cut ball, slag darts, and slag cut stopper are not used, and when the plastic of Patent Document 4 is added, at the end of tapping, the outflow from the tapping hole changes from molten iron to molten slag. , 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-11-241116 Japanese Patent Application Laid-Open No. 2006-152370 Japanese Patent Publication No. 52-32604

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

Including slag cut balls and slag darts, which have been conventionally used as a method for preventing slag in the converter, are put into the converter during tapping, float in the molten metal, and prevent slag from flowing out at the end of tapping. The stopper is hereinafter generically referred to as a "slag cut plug". By inserting a slag cut plug into the converter at the end of tapping, the amount of slag that flows into the ladle is reduced compared to the case where the slag is prevented from flowing out by tilting the converter without using a slag cut plug. can be reduced. However, the reduction of the amount of slag flowing into the ladle was by no means sufficient. In addition, even if the slag cut plug is inserted directly above the tapping hole, the slag cutting plug floats after the tapping and deviates from the position directly above the tapping hole, so that the tapping hole cannot be closed at the end of tapping.

The slag-cutting stopper described in Patent Document 3 has a complicated shape and is expensive, and it is not easy to install it in a tapping hole of a converter before molten iron is charged. In addition, in the method of adding plastic to slag on molten steel described in Patent Document 4, only the surface layer of the slag is cooled, so the effect of suppressing slag outflow near the interface between molten steel and slag is small. There was a problem that the work environment deteriorated because the gas generated by the thermal decomposition of the plastic spouted from the tilting furnace throat.

INDUSTRIAL APPLICABILITY The present invention is a method for preventing outflow of slag in a converter using a slag cut plug, which can sufficiently reduce the amount of slag flowing out to a ladle, and can reliably close the tap hole when tapping is finished. An object of the present invention is to provide a method for preventing outflow of slag in a converter.

That is, the gist of the present invention is as follows.
[1] A method for preventing outflow of slag in a converter using a slag cut plug when taking out molten iron from a tapping hole of the converter, comprising:
In advance, measure the time from the start of hot water discharge until the presence of slag in the hot water flow is confirmed, and set it to X (seconds),
By inserting the slag cut plug directly above the tapping hole after the tapping flow starts to swirl and before the X (seconds) elapses from the start of tapping, when 1/3 of the total tapping time elapses A method for preventing outflow of slag in a converter, characterized in that the slag cut plug has been completely inserted .
[2] A method for preventing outflow of slag in a converter using a slag cut plug when taking out molten iron from a tapping hole of the converter, comprising:
In advance, measure the time from the start of hot water discharge until the presence of slag in the hot water flow is confirmed, and set it to X (seconds), and measure the time from the start of hot water discharge until the hot water flow starts to swirl. is Y (seconds),
After Y (seconds) from the start of hot water discharge and before the X (seconds) from the start of hot water discharge, by inserting the slag cut plug directly above the hot water discharge hole, when 1/3 of the total hot water discharge time has elapsed, A method for preventing outflow of slag in a converter, characterized in that the slag cut plug has been completely inserted .

The present invention relates to a method for preventing slag in a converter from flowing out by using a slag cut plug when molten iron is taken out from a tapping hole of a converter, wherein the slag is removed from the tapping flow after the tapping flow starts to swirl. By inserting a slag cut plug directly above the tapping hole before the mixture of can be closed with a slag cut plug.

FIG. 4 is a schematic diagram of a situation and a period during hot water supply;

Hereinafter, an example will be described in which molten steel is refined using a converter and tapped from a tap hole. The same can be applied to the case where dephosphorization is performed in a converter to form molten iron and the molten iron is tapped from tapping holes.

When the steel is tapped from the converter, the depth of the bath in the converter decreases with the passage of time after the start of tapping. do. It is thought that as the depth of the depression increases, the slag floating on the molten steel is caught in the tapping flow and flows out from the tapping hole, thereby advancing the slag outflow to the ladle. Furthermore, it is known that at the end of the completion of tapping, slag flows out significantly from just before the outflow of molten steel is completed. A slag cut plug is a refractory object (a slag cut ball is a sphere) whose specific gravity is adjusted between that of molten steel and slag. The slag cut plug prevents slag from flowing out of the tapping hole even during tapping, and closes the tapping hole when tapping is completed, thereby suppressing slag outflow at the final stage of tapping.

However, the problem with using the slag cut plug is that the slag cut success rate (success rate of closing the steel tapping hole with the slag cut plug at the end of tapping) is low, and even if the slag cut is successful, slag may flow into the ladle. It was a lot.

Therefore, the present inventors conducted a water model experiment simulating the steel tapping phenomenon of the converter. Prepare a transparent acrylic container and connect a drain nozzle to the center bottom of the container. Water is placed in a container, and tracers (resin grains) are floated on the surface of the water. Insert a ball (made of styrene) just above the drainage nozzle in the middle of drainage. Then, as the water depth in the container decreased due to the progress of the drainage, the behavior of the drainage particles and the outflow behavior of the tracers (resin particles) floating on the water surface were observed.

As a result, we found the following.
Observing the drainage flow without throwing a ball into the water, we found that as the water level decreased, a dent was first formed on the surface of the water directly above the drainage outlet. , and after that point tracer started to flow out of the drain nozzle. A swirling flow is observed in the drainage flow near the drainage nozzle during the period from when the depression starts to occur until the depth of the depression reaches the height of the drainage nozzle. When the liquid depth in the container becomes shallow, a dent occurs on the water surface directly above the drain nozzle due to the suction flow to the drain nozzle, regardless of the presence or absence of the swirling flow. It is presumed that when the swirling flow is formed, the depression will become even deeper with the addition of the centrifugal force due to the swirling flow.

Next, we put a ball in the middle of the drainage and observed the drainage flow. If the ball is thrown in before the dent is formed directly above the drain port, the ball floats outside the nozzle axis and does not contribute to the suppression of outflow. On the other hand, after the dent reaches a certain depth and after a swirling flow is observed near the drainage nozzle (before the bottom of the dent reaches the height of the nozzle), if the ball is thrown in, the ball rotates. It remained in the dent, reducing tracer outflow into the drainage, and finally the ball was reliably fitted into the drainage nozzle, contributing to the suppression of outflow. On the other hand, when the ball was thrown in after the deepest part of the pit had reached the height of the drain nozzle, tracer outflow had already started. Therefore, it was found that controlling the ball injection timing from the generation of the swirling flow near the drainage nozzle until the deepest part of the depression reaches the drainage nozzle is the key to increasing the success rate of slag cutting. .

Next, the phenomenon was observed when molten steel was actually tapped from the converter. The furnace volume of the converter is a 100-ton converter, and the diameter of the tap hole is 125 mm.

Observing the surface of the molten metal in the converter during tapping, of course, only the surface of the molten slag is observed, and the state of the interface between the molten steel and the slag cannot be observed. From the observation of the surface of the molten slag, neither the generation of depressions at the molten steel-slag interface nor the swirling flow in the molten steel can be observed.

Therefore, we observed the tapping flow from the tapping hole to the ladle. At the start of tapping, neither swirling of the tapped stream nor slag inclusion in the tapped stream is observed. When the time elapsed from the start of tapping, the tapping flow began to swirl, and a phenomenon of flowing down while swirling was observed, and thereafter the swirling flow continued. The turning cycle of the tapping flow was about 1 second. Furthermore, as time passed after the occurrence of the swirling flow, a phenomenon in which slag was mixed in the tapped stream was observed. continued.

According to a comparison between the observation results of the water model experiment and the observation results of the steel output flow from the converter, if a slag cut plug is inserted after a swirling flow is observed in the output steel flow, the slag cut plug can be kept just above the tapping hole, and if the slag cut plug is inserted before slag is mixed in the tapping stream, the outflow of the slag that flows out along with the tapping stream can be largely prevented. I came up with the idea.

In order to insert the slag cut plug before slag is mixed in the tapped stream, it is necessary to know in advance when the slag will be mixed. Therefore, as a result of observing the tapping flow over a total of 100 heats, it was confirmed that the time required from the start of tapping to the start of slag mixing was almost the same with good reproducibility. Therefore, the time required from the start of tapping to the start of slag mixing is measured in advance, and the average value is defined as "X seconds".

Next, a slag-cutting ball was prepared as a slag-cutting plug, and the slag-cutting effect was compared by changing the timing of inserting the slag-cutting plug into the surface of the melt during tapping.

As a slag cut ball, the main composition in mass% is _Cr2O3 : 40%, _Fe2O3 : 25%, MgO: 10%, _SiO2 : ₁₀ % _{, Al2O3} : ₁₀ %, and the balance: A slag cut ball with a diameter of 220 mm and a weight of 26 kg was used by using a refractory material which was an impurity, and equipped with an iron core inside. The slag cut ball has a specific gravity of 4.67, which is intermediate between the specific gravities of molten steel and slag. Before the start of tapping, a chute for slag cut balls is charged into the furnace from the throat of the converter. At a predetermined timing during tapping, the slag cut ball was rolled from a chute toward molten slag in a liquid phase existing in the vicinity directly above the tapping hole. A required time (T seconds) is required from when the slag cut ball is instructed to start dropping to when the slag cut ball rolls down the chute and reaches (throws in) the surface of the melt. Hereinafter, the time when the command to start dropping is issued is called "dropping", and the time when the slag cut ball actually reaches the molten material is called "throwing".

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 the end of blowing, the furnace body is tilted to start tapping. The time required from the start of tapping to the end of tapping (steel tapping time) was 120 seconds. The period (T seconds) from the time when the slag cut ball was dropped (issued a command to drop) to the time it was dropped (arrived at the molten material in the converter) was 2 seconds.

The time (X seconds) from the start of tapping to the start of mixing of slag in the tapped stream was measured in advance. As for the mixture of slag in the tapped stream, the appearance of the tapped stream was imaged with a video camera and observed by image analysis to determine the appearance of the tapped stream because the brightness of the surface of the tapped stream differs between molten steel and slag. As a result, X=18 seconds. Observation of the tapping flow can also be performed visually through light-shielding glasses.

During tapping, the tapping flow was visually observed through light-shielding glasses to identify the turning start timing of the tapping flow. Figure 1 shows a schematic diagram of the situation and period during tapping. The period from the start of tapping to the start of turning of the tapping flow was defined as "period A", the period from the start of turning of the tapping flow to X seconds was defined as "period B", and the period from X seconds to the end of tapping was defined as "period C". The time required from the start of tapping to the start of turning of the tapping flow was approximately 5 seconds.

Then, the amount of slag flowing out to the ladle was compared when the slag cut balls were charged in any of the periods A, B, and C described above. The outflow amount of molten slag was calculated by the following method. That is, insert an iron rod into the surface of the molten material in the ladle after tapping is completed, measure the thickness of the slag layer attached to the recovered iron rod, and multiply the cross-sectional area of the ladle by the density of the slag. Then, the outflow amount of molten slag was calculated. 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.

Table 1 shows the molten slag flow rate obtained.

Comparative Example 1 is the case of throwing in period A (an instruction to drop a ball is issued at the same time as the start of tapping, and the ball is thrown two seconds after the start of tapping), and the thrown ball is on the tapping hole axis and outside the vortex. In many cases, the slag drifted and did not contribute to the suppression of slag outflow. In this case, when a large amount of slag flowed into the ladle, it was visually determined that the steel output had ended, and the converter was tilted to end the steel output. Therefore, a large amount of slag of 6.0 kg/t flowed out.
Example 1 is a case where the ball is thrown in period B (a ball-throwing instruction is issued 1 second after the turning of the tapping flow starts, and the ball is thrown about 8 seconds after the tapping start), and the thrown ball is directly above the tapping hole. It stayed on the tapping hole axis while rotating at , and it was possible to prevent slag from being mixed into the tapping flow to a minimum even during period C during tapping, and furthermore, the tapping hole was closed at the end of tapping. Therefore, the outflow of slag was suppressed to a small amount of 3.0 kg/t.
Comparative Example 2 is the case where the slag was introduced during the period C (the ball was introduced 50 seconds after the start of the tapping). , the slag outflow amount was 4.5 kg/t, which was higher than in period B.
Therefore, period B in Example 1 was the charging timing at which the slag outflow amount could be suppressed most.

Based on the above results, the present invention provides a method for preventing the outflow of slag in the converter using a slag cut plug when removing molten iron from the tapping hole of the converter. Measure the time from the start of hot water discharge until the time is confirmed to be X (seconds). A method for preventing outflow of slag in a converter, characterized by inserting a plug directly above the tapping hole.

When slag-cutting balls or slag darts are used as slag-cutting plugs in order to prevent slag from flowing out of the converter, the slag-cutting plugs have conventionally been thrown into the converter at the end of tapping as described above. However, as explained in detail above, in the case where the time required for tapping is about 120 seconds, the inventors of the present invention have found that slag has already begun to mix into the tapping stream 18 seconds after the start of tapping. It was clarified by the examination by et al. Therefore, the timing of inserting the slag cut plug is too late at the end of tapping, and slag has already flowed into the ladle before the slag cut plug is inserted. As in the present invention, by observing the tapping flow in advance, measuring the time (X seconds) from the start of tapping to the start of slag mixing into the tapping flow, and inserting the slag cut plug before X seconds, For the first time, it is possible to significantly suppress the inflow of slag into the ladle.

In addition, if the slag-cut plug is inserted too early, the slag-cut plug will float in the converter and will come out of the hole directly above the tapping hole. If the slag cut plug is inserted after the start of tapping, the inserted slag cut plug is held directly above the tap hole, so that the tap hole can be reliably closed at the end of tapping. Since the timing to start mixing slag into the output stream comes after the timing to start swirling the output stream, the slag is surely cut during the period from the start of swirling of the output stream to the start of slag mixing into the output stream. It is possible to throw in a plug.

In the present invention, the introduction of the slag cut plug is completed before the start of slag mixing into the tapped stream. 0.15 times, that is, when 1/3 of the total tapping time has elapsed, the insertion of the slag cut plug has been completed. In this respect, it is clearly different from the conventional art in which the slag cut plug is put in at the end of tapping, and the prevention of slag outflow into the ladle by the present invention is a major factor that stands out.

In the present invention, the tapping flow is observed in the target heat, and the slag cut plug is introduced after the tapping flow starts to swirl. Further, in the present invention, the time from the start of hot water discharge until the hot water flow starts to swirl is measured in advance and set to Y (seconds). A slag cut plug may be inserted directly above the tapping hole before the elapse of . The stream of steel output can be observed visually through light-shielding glasses, or a video camera can be used.

As the slag cut plug used for preventing slag outflow in the present invention, a spherical slag cut ball (slag ball) as described in Patent Document 1 and Non-Patent Document 1, as described in Patent Document 2 A slug dart, or a Saturn-shaped slug cut ball in which a disk is provided on the circumference of a spherical ball can be used.

As a method of charging the slag cut plug directly above the tapping hole in the converter, there is a method using a charging chute as described in Patent Document 5, and a method of lifting the slag cut plug using a lifting tool provided on the slag cut plug and charging it. , as described in Patent Document 1, any method can be used, such as a method in which a slag-cut ball is suspended by a wire and inserted into a converter, and the wire is fused to separate the slag-cut ball from the holder. can.

Claims (2)

A method for preventing outflow of slag in a converter using a slag cut plug when taking out molten iron from a tapping hole of the converter, comprising:
In advance, measure the time from the start of hot water discharge until the presence of slag in the hot water flow is confirmed, and set it to X (seconds),
By inserting the slag cut plug directly above the tapping hole after the tapping flow starts to swirl and before the X (seconds) elapses from the start of tapping, when 1/3 of the total tapping time elapses A method for preventing outflow of slag in a converter, characterized in that the slag cut plug has been completely inserted . A method for preventing outflow of slag in a converter using a slag cut plug when taking out molten iron from a tapping hole of the converter, comprising:
In advance, measure the time from the start of hot water discharge until the presence of slag in the hot water flow is confirmed, and set it to X (seconds), and measure the time from the start of hot water discharge until the hot water flow starts to swirl. is Y (seconds),
After Y (seconds) from the start of hot water discharge and before the X (seconds) from the start of hot water discharge, by inserting the slag cut plug directly above the hot water discharge hole, when 1/3 of the total hot water discharge time has elapsed, A method for preventing outflow of slag in a converter, characterized in that the slag cut plug has been completely inserted .

Images