JP2551013B2 - AOD furnace - Google Patents

Description

Detailed Description of the Invention

(Industrial field of application) The present invention is applied to alloy steel, especially stainless steel.
D related to improvement of AOD furnace used for refining method (argon-oxygen decarburization method), more specifically, eliminating convection dead zone of molten steel during refining, reducing splash of splash,
The present invention relates to an AOD furnace capable of shortening refining time. (Prior art) The AOD refining method is a method of decarburizing by blowing an inert gas such as Ar and N ₂ together with oxygen gas into molten steel at atmospheric pressure to reduce the CO partial pressure and suppress the oxidation loss of Cr. In this method, the mixed gas of oxygen and the inert gas is blown from several tuyere installed on the side wall near the furnace bottom. AOD furnace wall refractory is eroded by acid slag with low viscosity and violent infiltration in the initial stage, and further the slag and molten steel are vigorously stirred by the mixed gas injected into the molten steel in the furnace from the tuyere at the bottom of the side wall. Causes severe wear phenomena on the wall refractory surface. In addition, the molten steel temperature rises to over 1750 ° C due to the heat of reaction between the mixed gas blown in a large amount and the molten steel components, so that the melting loss of the refractory bricks especially at the tuyere and around the tuyere is remarkable. Therefore, in comparison with the tapped side furnace wall on the opposite side, the refractory brick was lined in advance with a thickness of 100 to 250 mm for the tuyere side furnace wall. (Problems to be solved by the invention) In the first place, the AOD refining method can easily change the mixing ratio of O ₂ and the inert gas, and the carbon concentration in the molten steel is decarburized from the high carbon region to the low carbon region. The decarburization efficiency was improved by lowering the O ₂ ratio as the temperature increased, and rapid and effective refining was enabled by vigorous bath agitation by blowing gas from the tuyere at the bottom of the furnace side wall. It has its characteristics. However, even though it is generally said that such excellent characteristics are present, in the actual operation of AOD refining, a part where the hot water does not go well, that is, a so-called dead zone occurs, or the amount of splash generation is large. Many problems have been pointed out. It is possible to prevent the dead zone of molten steel convection by increasing the amount of mixed gas and the amount of O ₂ blown into the molten steel to some extent, but these not only increase the splash amount,
Since the gas amount and O ₂ ratio of the mixed gas are closely related to the decarburization efficiency as described above, they cannot be simply increased. Therefore, the present inventor has scrutinized and examined the shape of the AOD furnace and the lining method of the refractory bricks, and as a result, in the AOD furnace, the tuyere side furnace wall and the tapped side furnace wall have a refractory brick lining thickness. Because of the difference as described above, we focused on the fact that the center of the furnace body and the center of the substantial inside of the furnace lined with bricks, that is, the center of the molten steel are deviated. That is, FIG. 2 shows the lining condition of the refractory brick in the cross section at the tuyere height of the conventional AOD furnace, in which the permanent tension brick 4 made of the fired magnesia brick is placed inside the iron shell 3. Further, a fan-shaped lining brick 5 made of magrophilic direct bond brick is laid on the inside thereof. Of the liner bricks 5, the liner bricks 5 (5a) on the tuyere side furnace wall are about 1.5 times thicker than the liner bricks 5 (5b) on the tapped side in order to prepare for the severe wear and high temperatures mentioned above. It is lined. Further, the refining gas is blown into the molten steel from the position of the tuyere brick 2 into the molten steel by the toyers, and the direction thereof is set to face the center C of the furnace body. As described above, in the conventional AOD furnace, the tuyere direction differs from the center C of the furnace body in spite of the fact that the lining thicknesses on the tuyere side and the tapped side are different and the inner shape of the furnace is asymmetrical. The problem of being suitable became clear. Therefore, the refining gas is blown to the front side of the center of the molten steel inside the furnace, and convection of the molten steel and refining reaction occur from that point and do not participate in the reaction near the tapped side furnace bottom. It is considered that a dead zone of molten steel is created. In addition, due to the occurrence of such a dead zone, convection of molten steel and refining reaction locally occur, and the amount of molten steel involved in refining with respect to the amount of gas blown is reduced, resulting in coarse gas bubbles and decarburization. It is expected that the efficiency will decrease and the amount of splash will increase. (Object of the Invention) The present invention has been made to solve the above problems, and an object of the present invention is to prevent the occurrence of a dead zone of molten steel convection and reduce the amount of splash, and further to this. Based on the improvement of steelmaking yield and efficiency.

Configuration of the Invention

(Means for Solving Problems) The present invention has been made in consideration of the AOD furnace shape in which the refractory brick lining is asymmetrical, and the refining gas blowing direction of the AOD furnace is deeper than the furnace center. By directing it toward the molten steel central part, the dead zone of the refining reaction is eliminated and the efficient refining throughout the furnace proceeds smoothly, and the gas bubbles become finer, reducing the amount of splash generation and shortening the refining time. In the AOD furnace of the present invention, the intersection of the blowing lines of the refining gas blown into the furnace from the plurality of tuyere provided on the furnace side wall is located at a position displaced from the center of the furnace to the far side. It is characterized by being. In the present invention, the blowing direction of the refining gas does not necessarily have to be completely coincident with the center of the molten steel.
The distance from the center of the furnace body may be set in consideration of capacity, operating conditions, etc. However, if the displacement is small, the effect of eliminating the dead zone is small and conversely if it is too large, damage to the refractory brick on the tapped side becomes severe. A tendency is recognized, and it can be said that the preferable range is 50 to 250 mm. (Example) FIG. 1 shows a 20 ton AOD furnace according to an embodiment of the present invention. In the longitudinal sectional view (a), the AOD furnace 1 is inside the iron shell 3 having a furnace outer diameter D = 2900 mm, as compared with the case of FIG. Similarly, a permanent brick 4 made of fired magnesia brick and a lining brick 5 made of magrophilic direct bond brick are placed inside the brick, and the thickness t ₃ and t ₄ of the lining brick 5 at the upper part of the furnace are Is also 280 mm. FIG. 1 (b) shows a cross section of the AOD furnace 1 at the tuyere height AA, showing the lining thickness t ₁ of the tuyere side lining brick 5 (5a) and the tapping side lining brick. The lining thickness t ₂ of 5 (5b) is 550 mm and 330 mm, respectively, and the tuyere brick 2 faces the position P where the refining gas is closer to the tapped side furnace wall by the distance d = 150 mm from the furnace center C. Has a simple structure. As a result of applying the AOD furnace 1 having such a shape and structure to the refining of the low C austenitic stainless steel SUS 304L, it was found that it took about 60 minutes to decarburize the C content to 0.015% in the conventional AOD furnace of the same capacity. About 5 refining times without changing operating conditions
It was confirmed that it could be reduced to 0 minutes. In addition, it was revealed that the amount of splash generated could be reduced to about 400 kg from the conventional amount of about 800 kg per charge.

As described above in detail, the present invention makes it possible to prevent the generation of dead zones and reduce the amount of splash generation during refining by directing the refining gas blowing direction of the AOD furnace toward the molten steel center. In particular, it greatly contributes to the improvement of steelmaking yield and efficiency in refining low C stainless steel and the like.

[Brief description of drawings]

1 (a) and 1 (b) are longitudinal sectional views and transverse sectional views at the tuyere height, respectively, showing the structure of the AOD furnace in the embodiment of the present invention, and FIG. 2 is the tuyere height showing the structure of the conventional AOD furnace. FIG. 1 …… AOD furnace, 2 …… tuyere brick, 5 …… lining brick, 5a …… tuyere side lining brick, 5b …… steel side lining brick, C …… hearth center.

Claims (2)

(57) [Claims] 1. An intersection of blow-out direction lines of the refining gas blown into the furnace from a plurality of tuyere provided on a side wall of the furnace is located at a position displaced from a center of the furnace body to a far side. AOD
Furnace. 2. The shifted position is 50 to 250 m from the center of the furnace.
The AOD furnace according to claim (1), which is located at m.