JPS5848609B2 - Method and device for refining molten steel with slag removal in an inert gas atmosphere - Google Patents

Description

[Detailed Description of the Invention] Simply put, refining molten steel means removing harmful impurities, and sulfur in molten steel is one of the elements harmful to steel.

Normally, steel contains about 0.010 to 0.030% sulfur, but when manufacturing thick structures by welding or manufacturing high-strength steel, the sulfur content is reduced. 0.
It is desirable that the sulfur content be 0.010% or less, and if a high quality continuously cast slab is desired, the sulfur content should be 0.010% or less.
0.010% or less is preferable.

Conventional desulfurization methods are carried out in CAm cracking furnace,
(B) It may be carried out in the ladle after tapping.

(A) When the process is carried out in a melting furnace, the refining atmosphere is made into a reducing atmosphere and (a) sulfur is absorbed into the slag by the reaction between the molten steel and the slag covering it.

At this time, it is preferable that the slag has a large CaO component.

(mouth) Elements that easily react with sulfur in molten steel, such as Mn
Rare earth elements and the like are added as desulfurization agents, and sulfur is absorbed into the slag in the form of sulfides of those metals.

(B) When the process is carried out in a ladle, the molten steel is heated electrically, mechanically,
Stirring is performed by a method such as gas injection, and deflow refining is performed by methods (a) and (x) such as in the above-mentioned melting furnace.

To summarize the conventional method described above, the sulfur in the steel is transferred and absorbed into the slag covering it.

The basic conditions include (a) a reducing atmosphere (a neutral atmosphere may be used), and (b) a slag with a high CaO content.

Therefore, if these basic conditions change, desulfurization will not proceed sufficiently.

For example, (Z) the reducing atmosphere becomes weaker and eventually becomes an extremely oxidizing atmosphere, (the CaO content in the slag decreases and the SIO2 content increases, etc.). The absorption capacity decreases, and not only does the capacity disappear completely, but the sulfur absorbed in the slag returns to the molten steel, that is, resulfurization occurs, and in extreme cases, all of the sulfur returns to the molten steel.

Another problem is that slag has a limited ability to absorb sulfur.

Therefore, in order to further desulfurize, it is necessary to repeatedly perform desulfurization refining by removing the slag that has absorbed a large amount of sulfur, covering the molten steel with new slag, and allowing the new slag to absorb sulfur again.

In addition, in recent years, various methods have been studied to desulfurize molten steel by stirring it in a ladle, but all of them have low desulfurization rates and are extremely difficult to reduce the sulfur content in steel to 0.010% or less. be.

Therefore, the present invention solves the problems of the conventional method by performing desulfurization in an inert gas atmosphere without oxygen. The lower end of the molten steel lift pipe is immersed in the molten steel in the ladle to make the atmosphere inside the ladle airtight and to maintain an inert gas atmosphere in the refining chamber. By adjusting the pressure, the molten steel is brought into the refining chamber through the molten steel lift pipe, and the surface of the molten steel in the refining chamber is covered with refining slag to perform refining in an inert gas atmosphere. This invention relates to an apparatus for refining molten steel accompanied by slag removal in an inert gas atmosphere, characterized in that upper surface slag is removed in an inert gas atmosphere.

Embodiments of the present invention will be described below with reference to the drawings.

The lower end of the cover 5 formed to surround the refining chamber 4 is placed over the airtight container 3 which surrounds the ladle 1 containing the molten steel 2 to form an airtight atmosphere.
It is airtightly attached with a bolt 7 via a 1J ring 6.

A molten steel elevator pipe 8 whose lower end extends into the molten steel 2 in the ladle 1 is provided in the lower part of the refining chamber 4 .

Further, an additive material charging device 9 and an inert gas inlet/outlet 10 are provided in the upper part of the refining chamber 4, and the inert gas inlet/outlet 10 is provided with a connecting pipe 11 which is cooled by cooling water as shown by an arrow. A retractable bag 12 made of leather or the like is connected via a.

In the figure, 13 is a heating device provided above inside the refining chamber 4.

A slag outlet 14 and a door 15 are provided at an appropriate height position on the side surface of the smelting chamber 4. By opening the door 15 and inserting a slag removal device 16 provided outside the smelting chamber 4, slag removal can be carried out. The slag 17 on the upper surface of the molten steel in the chamber 4 can be scraped out into the slag pot 18.

Further, in order to maintain an inert gas atmosphere when the door 15 is opened, a seal chamber 20 is provided which surrounds the slag pot 18, supports the sludge removal device 16 in an airtight manner so as to be slidable, and is provided with a peep hole 19. is provided outside the refining chamber 4.

In the figure, 21 is a supply/exhaust hole provided in the cover 5 to adjust the pressure inside the airtight container 3 (ladle atmosphere), and 22 is a refining chamber for smooth and complete outflow of the molten steel 2. A sloped portion 42 formed at the bottom of the slag pot 4 is a lid having a sealing function for taking the slag pot 18 in and out.

FIG. 2 shows the details of the support part of the sludge removing device 16 in the seal chamber 20. The support part is provided with a universal seal 23, and the unihersal seal 23 is 0 1
A sealing ball 27 that grips the scraping rod 26 of the sludge removing device 16 via the J-rings 24 and 25, and an O
It consists of two hemispherical seal shells 30 that are gripped via rings 28 and 29, and this structure allows the scraping rod 26 to rotate while maintaining airtightness inside and outside of the seal chamber 20. It has become.

In addition, two rotating rods 32 (one is omitted in the illustration) are provided in the sealing chamber 20 to support a round rod 31 for supporting the scraping rod 26. The lower end of the rod 32 is pivotally connected to the inner surface of the sealing chamber 20 by a pin 33.

Also provided is a rod 36 which passes through the seal chamber 20 and whose penetrating portion is held airtight by a seal ring 35 equipped with an 01J ring 34, and the rod 36 is driven by a motor 37 provided outside the seal chamber 20. Warm Gya 38
The inner end of the seal chamber 20 is connected via a pin 41 to the end of an arm 40 which is connected to the rotating rod 32 by a pin 39.

Therefore, by driving the motor 37 to push and pull the rod 36 left and right to rotate the rotary rod 32, the round rod 31
The scraping rod 26 can be rotated vertically around the universal seal 23 by changing the height position of the scraping rod 26.

In the configuration described above, first, the inside of the refining chamber 4 and the inside of the sealing chamber 20 are filled with inert gas using an appropriate method.

At this time, the gas inside the expandable bag 12 is removed and the bag 12 is contracted.

Next, when high-pressure air or inert gas is supplied from the supply/exhaust hole 21, the pressure inside the airtight container 3 increases, and the molten steel 2 in the ladle 1 flows into the refining chamber 4 through the molten steel elevator pipe 8. Therefore, the pressure inside the airtight container 3 is adjusted and kept constant so that the height of the molten steel 2 flowing into the refining chamber 4 becomes an arbitrary height H.

At this time, as the molten steel 2 flows into the refining chamber 4, the space within the refining chamber 4 becomes narrower, so that inert gas is sent into the expansion/contraction bag 12.

Next, slag material is introduced from the additive material charging device 9 provided at the upper part of the refining chamber 4, and the molten steel 2 is refined by turning the slag material into slag, and the ladle atmosphere is further pressurized and depressurized repeatedly. By moving the molten steel 2 into and out of the refining chamber 4, refining is repeatedly performed.

At this time, the molten steel 2 is heated by a heating device 13 in order to maintain the fluidity of the molten steel.

When refining is completed, fluid is further introduced through the supply and exhaust holes 21 to increase the pressure inside the airtight container 3, thereby pushing up the molten steel 2 in the ladle 1, so that the upper surface of the molten steel 2 in the refining chamber 4 becomes slag. Adjust the height H' so that it is at the lower side of the outlet 14 (slightly lower than the lower side).

Next, the door 15 is opened, and the height position of the scraping rod 26 of the sludge removing device 16 is adjusted via the rod 36, rotating rod 32, and round rod 31 by operating the motor 37, and the slag removal port 14 is opened. After adjusting the height of the scraping rod 26 again to a height suitable for scraping out the slag 17, the scraping rod 26 is pulled out and the slag 17 is scraped out into the slag pot 18.

At this time, the inside of the seal chamber 20 is also kept in an inert atmosphere because it has an airtight structure.

When the slag removal is completed, the pressure inside the airtight container 3 is lowered, and all of the molten steel 2 in the refining chamber 4 is returned to the ladle 1, thereby completing the refining work of the molten steel 2.

As mentioned above, even if the amount of molten steel changes in the refining chamber 4, the inert gas is released into the expansion bag 12 and returned again, so the inside of the refining chamber 4 is always kept in an inert atmosphere. Since the ladle atmosphere pressure can be changed and the height of the top surface of the molten steel 2 in the refining chamber 4 can be easily and reliably adjusted.

As a result of experiments conducted according to the present invention, the sulfur content in the molten steel 2 could always be reduced to about 0.004 to 0.007%.

It should be noted that the present invention is not limited to the above embodiments, and that the expandable bag can be made of other materials and have various shapes, and that the slag removal method, sealing chamber shape, and sealing method are not shown in the drawings. Of course, it is possible to adopt various other configurations, and to make various other changes without departing from the gist of the present invention.

According to the method and apparatus for refining molten steel with slag removal in an inert atmosphere of the present invention described above, (1) By performing the refining in an inert gas atmosphere, sulfur is more fully contained in the slag. Therefore, more sufficient desulfurization is possible than in the atmosphere.

(11) Since slag is removed in the refining chamber, when the molten steel is returned to the ladle, it is completely unlikely that sulfur will return to the molten steel in the ladle.

(iii) Since slag is removed in the smelting chamber, there is no need to worry about slag remaining at the bottom of the smelting chamber and reducing the desulfurization effect of the next treatment when the molten steel is returned to the ladle. .

(1v) Since slag is removed from the refining chamber in an inert atmosphere, there is no risk of resulfurization during slag removal.

(v) Since the depth of the molten steel in the refining chamber is relatively shallow, the slag metal reaction can easily proceed and the desulfurization effect can be improved, and if the molten steel is stirred mechanically or electromagnetically, it can be even better. You can expect good results.

(1) Since the refining slag can be replaced as many times as necessary, desulfurization efficiency can be improved.

~1) By providing the expandable bag, it is possible to maintain an inert atmosphere in the refining chamber at all times economically and easily.

etc., exhibits various excellent effects.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of the present invention, and FIG. 2 is a detailed explanatory diagram of a support portion of a slag removal device for a sealing chamber. 1 is a ladle, 2 is molten steel, 3 is an airtight container, 4 is a refining chamber, 5 is a cover, 8 is a molten steel elevator pipe, 9 is an additive charging device, 10 is an inert gas inlet/outlet, 12 is an expansion bag, 14 is slag outlet, 15 is a door, 16 is a sludge removal device, 17 is a slag, 20 is a seal chamber, 21 is an air supply/exhaust hole, 23 is a universal seal, 26 is a scraping rod, 30 is a seal shell, 31 is a round bar, 32 is a rotating rod, 36 is a rod, 37 is a motor, and 38 is a worm gear.

Claims (1)

[Scope of Claims] 1. A refining chamber having a molten steel elevator is located above the ladle, and the lower end of the molten steel elevator is immersed in the molten steel in the ladle to make the ladle atmosphere airtight. By maintaining an inert gas atmosphere in the refining chamber and adjusting the pressure of the ladle atmosphere, molten steel is brought into the refining chamber through the molten steel elevator pipe, and the surface of the molten steel in the refining chamber is covered with refining slag. A method for refining molten steel accompanied by slag removal in an inert gas atmosphere, characterized in that the slag on the upper surface of the molten steel is removed in the inert gas atmosphere after refining. 2. A refining chamber is provided in the upper part of the ladle, and is equipped with a molten steel lift pipe whose lower end is immersed in the molten steel in the ladle, and the inside is maintained in an inert gas atmosphere, and the ladle atmosphere in the lower part of the refining chamber is maintained. It has an airtight and pressure adjustable structure, and is equipped with a slag outlet and a slag removal device for taking out slag from the outlet, and can maintain them in an inert gas atmosphere at an appropriate side position of the refining chamber. A molten steel refining device that removes slag in an inert gas atmosphere and is equipped with a seal chamber.