JPS60114513A - Decreasing method of inclusion - Google Patents

Abstract

PURPOSE:To remove effectively the inclusions in a molten steel in a stage of supplying the molten steel via a tundish to a casting mold by disposing plural pieces of gates having a specific construction into the tundish and passing the molten steel through the through-holes provided to the gates. CONSTITUTION:A molten steel 2 is supplied in a static flow state by an immersion nozzle 3 ito a tundish 1 in the stage of receiving the molten steel 2 from a ladle into the tundish 1 and supplying the same through a bottom nozzle 5 into a continuous casting mold, etc. Plural gates 4 provided with plural through- holes 7 having diameter d(cm), number (n) and sectional area Scm<2> of the flow passage for the molten steel satisfying the figures expressed by the equation (1) are installed at an interval Lcm in the tundish 1 so as to cross the flow passage for the molten steel 2. The molten steel 2 passes through the holes of the gates 4 and collides against the wall of the next gate 4 while the molten steel flows through the outlet of the nozzle 3 to the tundish nozzle 5. The inclusions contained in the molten steel are flocculated and aggregated by the turbulence generated in the molten steel in this stage and are stuck to the refractory wall of the gates, by which the inclusions are separated and removed. The clean steel is supplied through the nozzle 5 into the casting mold.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for reducing inclusions floating in molten steel in a channel-shaped container such as a tundish.

BACKGROUND OF THE INVENTION In recent years, with the need for higher quality steel, the reduction of inclusions that cause cracks has become important. In particular, various measures have been taken to reduce inclusions in tundishes used for continuous casting of steel. In other words, if we roughly categorize the currently used methods for reducing inclusions in tundishes, we can: (1) promote flotation separation using weir devices, (2) adsorption separation by inert gas injection, and (3) flocculation by utilizing turbulence.・Promotion of merging (Unexamined Japanese Patent Publication No. 55-33853), (
4) Removal by filter (Tetsu to Hagane January, 8916.1
883) etc.

However, according to methods (1) and (2), the effects are still insufficient when used alone, and it is necessary to use them in combination with other methods. Regarding method (2), in order to reduce inclusions and improve the clarity of steel,
Although it is necessary to refine the blown gas bubbles to about 2 to 5 m/m, a sufficient refinement effect cannot be obtained at present.

Regarding the method (3), there are an example described in Japanese Patent Publication No. 55-33853 and an example in which the stirring power of inert gas bubbles is utilized as shown in FIG. In FIG. 1, molten steel 2 injected from a long nozzle 3 passes through a through hole 7 of a weir 4, is stirred by Ar gas blown from a bottom-blown porous plug 6, and flows out from a tundish nozzle 5. It shows.

These methods utilize the generated turbulence to promote agglomeration and coalescence of inclusions floating in molten steel. process is required.

Regarding method (4), there is a drawback that if a filter having a pore size sufficient to ensure a flow hole for molten steel is used, the effect of reducing inclusions will not be enhanced.

OBJECTS OF THE INVENTION The present invention aims to advantageously solve these drawbacks and reduce inclusions in molten steel.

Structure and operation of the invention That is, the present invention provides a specific plurality of weirs having through holes in the cross-sectional direction of the molten steel flow path of the tundish, and utilizes the jet flow discharged from the through holes and colliding with the refractory wall of the weir. The present invention relates to a method for reducing inclusions in molten steel, which is characterized in that the inclusions that have aggregated, coalesced, and grown are efficiently stuck to a refractory and removed by generating local turbulence.

Hereinafter, the method of the present invention will be explained based on the drawings.

When injecting molten steel from a ladle into a mold in the continuous casting method or ingot making method, a tanditshu is used to make the injection flow of molten steel into a static flow.

As shown in Fig. 2(a), in the invention of Suiden 1,
Molten steel 2 is poured into a tundish l from a ladle or the like through a long nozzle 3, and the molten steel 2 that has passed through a plurality of weirs 4 is discharged from a tundish nozzle 5 and transferred to a mold. Note that the arrows in the figure indicate the direction in which molten steel flows.

In this case, as shown in Fig. 2(b), weirs 4 having n through holes with diameter d (cm) are installed at intervals of L (cm) M in the cross section of the tundish through which molten steel flows continuously. Place multiple pieces.

In addition, regarding the arrangement of the through holes of each weir, generally when fluid flows through through holes in the wall, nozzles, etc.
Since it is known that jets are ejected with a maximum divergence angle of 206 degrees, if adjacent jets are discharged with divergence angles within 20 degrees, as shown in FIG. 2(C), They shall be arranged so that they collide with the wall of the weir on the downstream side without overlapping each other, and the spacing between the weirs shall be determined accordingly.

Figures 3 and 4 show low-grade aluminum guild steel and 60t Ar
The results of an inclusion removal experiment using a shielded tundish are shown. Although alumina graphite bricks were used as the refractory material for the weir, other materials such as magcarbon bricks and lime bricks may also be used. Also table-
1 shows the various conditions that were set.

Table 1: Three weirs were used. In addition, as an index showing the effect of reducing inclusions, 53
An inclusion index η, which represents the number of inclusions obtained by the slime extraction method of pL or more in comparison with the conventional method, was used. The smaller the inclusion index, the greater the effect of reducing inclusions. Here, the conventional method refers to operation under the conditions shown in Table 2.

Table 2 Note that S represents the cross-sectional area of the molten steel flow path [Cm'] in a steady state.

Figure 3 summarizes the results and shows the weir spacing and through hole diameter d.
The relationship between the ratio L/d and the inclusion index η is shown. However, Q/d n in the graph is 80 for a circle, 60 for a square,
This represents the case where there are 40 triangles.

4≦L/d≦18. Further, a reduction effect was observed when Q/d n≧40.

FIG. 4 shows the relationship between the parameter Q/dnSL representing the stirring intensity and the inclusion index η when Q/dn is 80.

The effect was recognized when Q/dnSL was 10 or more.

From the above operational data, it was recognized that the effect of reducing inclusions appears under the conditions of the formula.

Next, Fig. 5 shows an example of the invention method of the youngest brother 2, which also uses stirring gas injection from below the molten steel bath surface. ,
Alternatively, stirring of the molten steel is promoted by blowing in a stirring gas such as an inert gas using an immersion lance, and the effect of adsorption and removal by agglomeration and coalescence of inclusions and bubbles is added.

Figure 6 shows the results of an experiment in which low-grade aluminum killed steel was injected into two rooms sandwiched by three weirs using a 60-ton A shield tundish and Ar gas was used as the stirring gas.

Table 3 shows the various conditions at that time.

Table 3 Ar gas was blown in a predetermined stoichiometric amount through two porous plugs provided at the bottom of the tundish between the bases. FIG. 6 shows the relationship between the blown Ar gas flow l Q A r and the inclusion index η. Kasu Ryusei QAr is 2 CN text/m1nel
It can be seen that the effect of removing inclusions appears above the weir section.

EXAMPLE Table 4 shows the results of continuous casting of low-order aluminum guild steel using a 60 t Ar-shielded tundish in a three-weir system under various conditions.

In addition, the molten steel temperature in this case is 1580'', and the cross-sectional area S of the C5 molten steel flow path is 8000 cnf, and when the spread angle of the discharged jet is set to 20°, the through hole of the weir is located on the downstream side instead of east. It was placed so that it would collide with the weir.

Nos. 11 and 12 are those in which A's dregs were blown into the bottom part between the bases from the porous plug, and the effect of reducing inclusions was more excellent.

[Effects of the Invention] - As described in detail, the method of the present invention causes a region of locally intense turbulence to be generated in the vicinity of the dam wall each time the jet discharged from the through hole collides with the weir wall on the downstream side. , a method that promotes the agglomeration and coalescence of inclusions floating in molten steel, efficiently moves them to the refractory wall, makes it possible to remove U adhesion, or adds an adsorption removal effect using air bubbles,
A method has become possible to reduce inclusions in molten steel and thereby stably improve slab quality.

Note that the method of the present invention can be applied not only to the production of steel but also to the production process of non-ferrous metals.

[Brief explanation of drawings]

Fig. 1 is an explanatory elevation cross-sectional view of a conventional example, Fig. 2(a),
(b) and (c) are IJIJ diagrams of the invention of this Section 1, Figure 2 (a) is an elevation sectional view, Figure 2 (b) is a perspective view showing the shape of the weir, and Figure 752 (c). Theory II describes the situation in which molten steel gushes out from a through hole in a weir. Figures 3 and 4 are graphs showing the effects of Mizui's invention. FIG. 5 is an explanatory diagram of the invention of Section 2, and is an elevational sectional view. FIG. 6 is a graph showing the effect of the invention of Sui-Tei 2. 1--Tandish nozzle, 2--Medium molten steel, 3--Long nozzle, 4--Weir, 5---Tandish nozzle, 6...Bottom-blown porous plug, 7...Through hole. Patent Applicant New 1 Wooden Iron Co., Ltd. Agent Patent Attorney Masaru Inoue Figure 1 Figure 2 (Q) Figure 2 (b) Figure 2 (C) Figure 3% Figure 4 91￥SL Figure 5b Figure 6 QAr (%in)

Claims (2)

[Claims] (1) In a tundish equipped with a plurality of weirs having through holes in the cross-sectional direction of the molten steel flow path, the plurality of weirs satisfy the conditions expressed by the following formula, where d is the diameter of the through hole (cm ), n5 number of through holes Q
: Molten steel flow Q (cm'/5ec), S; Molten steel flow path cross-sectional area (cm'), L + weir spacing (cm), MIN (
x・y): The minimum value of x and y is 1, and multiple weirs are arranged so that each jet stream discharged from the through hole collides with the wall of the bottle on the downstream side without overlapping; A method for reducing inclusions, characterized in that L. (2) In a tundish equipped with multiple weirs having through holes in the cross-sectional direction of the molten steel flow path, the multiple weirs satisfy the conditions expressed by the following formula, where d: Diameter of the through hole (cn+ ), n: number of through holes Q: molten steel flow rate (cm'/5ec), S: molten steel flow path cross-sectional area (cm'), L: weir interval (cm), MIN (
X, Y) =: X,! l:Minimum IC among 11
In addition, a plurality of weirs are arranged so that each jet stream discharged from the through hole collides with the wall of the downstream weir without overlapping, and further, from below the bath surface of a room separated by two weirs in the front and back, A method for reducing inclusions, characterized by blowing in stirring scum at a flow rate of 2 (N/win) or higher.