JPH03198952A - Method for supplying molten metal in continuous casting - Google Patents

Abstract

PURPOSE:To prevent drift of molten steel in a submerged nozzle and to improve the quality of cast slab by blowing gas through a porous refractory fitted as projecting from inner wall face at pushing-out side of a slider at upper part of inner hole in the submerged nozzle to restrain the drift of pouring stream. CONSTITUTION:The porous refractory 9 for blowing Ar gas 10, etc., from almost perpendicular direction to the drift of molten steel is fitted at upper part of inner hole in the submerged nozzle 7. As the molten steel stream poured into the submerged nozzle 7 through sliding gate 3 has tendency to drift to pushing- out side of the slider, the porous refractory 9 is fitted as projecting to the inner hole only at the pushing-out side of slider on inner wall face at the upper part of submerged nozzle. Shape and area of horizontal cross section of outlet hole of lower fixed plate 6 in the sliding nozzle 3 and the submerged nozzle pouring hole fitting the porous refractory 9 are desirable to be same. Further, the areas are desirable to be 60-80% the horizontal cross sectional area in the inner hole at straight barrel part of the submerged nozzle without the porous refractory.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a hot water supply method for preventing drift of molten steel in a submerged nozzle in a continuous casting method using a sliding gate and a submerged nozzle.

(Prior Art) In continuous casting, a stopper or a sliding gate is used to control the amount of molten metal supplied from the tundish to the mold and to stop the supply.

The stopper has the advantage that it can be reliably stopped because there are few fitting parts with the nozzle. However, the stopper can only be used for on-off control, and the stopper may become uncontrollable if its head melts or breaks. on the other hand,
Sliding gates can freely control the flow rate of the melt, and automatic control is possible if they operate according to the casting speed, so they have recently become widely used in place of stoppers. .

FIG. 1 is a vertical cross-sectional view showing a typical example of a conventional sliding gate type pouring device. As shown in FIG. The sliding gate 3 includes an upper fixed plate 4, a lower fixed plate 6, and a slider 5 that slides between these fixed plates in the direction of the arrow. The molten steel 2it8 flows from the tundish nozzle 2 attached to the tundish bottom refractory 1, passes through the sliding gate 3, descends through the immersion nozzle 7, and exits into the mold from the discharge ports 1a and 7b. Under the influence of the slider 5 that prevents the flow from moving straight, the molten steel flow 8 deviates from the nozzle center as shown in the figure, causing a drift in the submerged nozzle and a one-sided flow into the mold.

When this one-sided flow occurs, defects due to scene changes, powder entrainment, etc. are likely to occur in the slab.

For this reason, measures have been taken to prevent the drift of the molten steel flow in the immersion nozzle.
In 5923 J, the lower end of the inner hole of the immersed nozzle is shaped into a pool to suppress drifting of molten steel, and the immersed nozzle with discharge holes on the left and right sides (argon can be injected from the upper end to the left and right sides) is used to increase the amount of injection into the left and right A. However, if the left and right Ar blowers are controlled independently, the amount of A blowing into the nozzle increases.

This increases fluctuations in the molten steel scene within the mold, resulting in many undesirable effects such as uneven inflow of powder, disordered oscillation marks on the slab surface, and increased vertical cracking in medium carbon steel.

Furthermore, [JP-A-57-130745] proposes a method in which spiral grooves or protrusions are provided in the straight body of a submerged nozzle to give molten steel a swirling flow centered on the central axis of the nozzle. . However, the main purpose of this method is to cause the swirling flow to act as a shearing force on the inner wall of the nozzle and to prevent AlzOx from adhering to the inner wall. However, it cannot be said that this is sufficient for the purpose of equalizing the discharge amount of the left and right discharge holes.

Furthermore, the thickness of the refractory material becomes uneven in the straight pipe portion of the nozzle, making it more likely that cracks will occur due to heat shock.

(i!l!IJi to be solved by the invention) The purpose of the present invention is to solve the problems of the conventional continuous casting metal supply method using a sliding gate and an immersion nozzle. It is an object of the present invention to provide a hot water supply method capable of producing high-quality slabs by suppressing drifting, eliminating differences in the level of hot water in a mold, and preventing entrainment of powder and uneven distribution of inclusions.

(Means for Solving the Problems) The present inventor has conducted a cold model test using water and an actual machine test using a continuous casting machine to investigate the generation of drifting flow that occurs from the sliding gate to the immersion nozzle and how to suppress it. We obtained the following knowledge.

(AlAs shown in FIG. 1 mentioned above, the flow 8 discharged from the tundish nozzle 2 deviates from the center due to the influence of the slider 5 of the sliding gate, and in the submerged nozzle, it flows toward the closed side of the slider 5, The flow rate 8a of the discharge lower a of the immersion nozzle is larger than the flow rate 8b of the discharge lower b,
This causes a difference in flow rate.

(b) The flows 8a and 8b branching from the left and right discharge holes of the immersion nozzle have short-cycle and long-cycle flow velocity (flow rate) fluctuations, as shown in FIG. 3, which will be described later. Of these, it is impossible to suppress fluctuations that occur in short periods, but macroscopic fluctuations that occur in long periods can be suppressed by blowing gas from a direction almost perpendicular to the drifting flow in the nozzle. This can be resolved by directing the immersion nozzle toward the central axis.

(C) By suppressing macroscopic fluctuations, scene fluctuations, accompanying powder entrainment, and uneven distribution of inclusions can be significantly reduced.

The present invention has been made based on the above findings, and the gist thereof is ``a continuous hot water supply method using a sliding gate and an immersed nozzle, in which a continuous hot water supply method using a sliding gate and an immersed nozzle protrudes from the inner wall surface of the slider extrusion side at the upper part of the inner hole of the immersed nozzle. ``Continuous casting hot water supply method'' characterized by blowing gas through a porous refractory installed in a continuous casting method to control uneven flow of the injection amount.

When carrying out the method of the present invention, (1) set the gas blow gauge pressure to 1 to 4 kg/cm.
and the blowing flow rate is 5 to 10 Q/wi.
■ The installation range of the porous refractory is 50 MIm or more in the longitudinal direction from the upper end of the inner hole of the immersion nozzle, and the horizontal cross-sectional area of the injection hole of the porous refractory attachment part is within the straight body of the immersion nozzle. Use an immersed nozzle with a horizontal cross-sectional area of 60 to 80%; ■ The shape and horizontal cross-sectional area of the single hole of the immersed nozzle fitted with porous refractories should be the same as the shape of the exit hole of the lower fixed plate of the sliding gate and It is desirable to use an immersion nozzle with a horizontal cross-sectional area equal to the horizontal cross-sectional area.Although each of the above (1) to (4) may be carried out independently, it is most desirable to carry out all of them together.

Any gas may be used to blow in from the porous refractory for the purpose of preventing drift, but in consideration of the influence on the composition of molten steel, inert gas, especially Ar gas, is preferable.

(effect) Hereinafter, the hot water supply method of the present invention will be explained with reference to the drawings.

FIG. 2(a) is a longitudinal cross-sectional view of a main part of a water heater used in the method of the present invention, and FIG. 2(Φ) is a cross-sectional view taken along line AA in FIG. 2(a).

As shown in the figure, a porous refractory 9 into which, for example, ^r gas 10 can be injected is attached to the upper part of the inner hole of the immersion nozzle from a direction substantially perpendicular to the drift of molten steel. The molten steel flow injected into the immersion nozzle 7 through the sliding gate 3 is biased toward the slider extrusion side as shown in FIG.
), it is sufficient to attach the immersion nozzle so that it protrudes into the inner hole only on the slider extrusion side of the upper inner wall surface.

It is desirable that the horizontal cross-sectional shape and area of the outlet hole of the lower fixed plate 6 of the sliding gate 3 and the injection hole of the immersion nozzle to which the porous refractory 9 is attached are the same; It is preferably 60 to 80% of the horizontal cross-sectional area of the inner hole of the straight body.

If this value is less than 60%, it becomes difficult to control the discharge flow rate during the process of increasing the discharge flow rate in the initial stage of casting, and scene fluctuations tend to occur. On the other hand, if it exceeds 80%, the protrusion of the porous refractory 9 from the inner wall surface of the immersion nozzle is too small, the effect of gas blowing on the drifting of molten steel becomes weak, and the drifting inside the nozzle is not suppressed.

Further, it is desirable that gas is blown from the outside of the immersion nozzle into the inner hole of the immersion nozzle through a porous refractory, and the gas is uniformly supplied over a range of 50 m or more in the longitudinal direction. 50Il
If it is less than 11, the blown bubbles are insufficient to make the flow go straight, and the drift in the nozzle is not sufficiently suppressed.

Next, gas blowing conditions of the present invention will be explained.

Slabs were continuously cast under the conditions shown in Table 1 using the water heater shown in FIG. 2 described above.

Table 1 and FIG. 3 are diagrams schematically illustrating the relationship between the drifted flow in the nozzle, the flow velocity of the discharged flow, and scene fluctuations.

That is, as shown in Fig. 3(a), the flow velocity of the hot water coming out of the left and right nozzles is 2, respectively. 1. If VOI is set and the left and right scene heights are HL and H, then the flow velocity is 3rd with respect to the casting time.
The scene changes as shown in FIG. 3(b) and as shown in FIG. 3(c). The greater the degree of drift in the immersion nozzle, the greater the difference in flow rate between the left and right discharge ports at the lower end of the nozzle, and the greater the difference in scene level between the left and right short sides of the slab mold. In other words, the difference in the level of the hot water on both the left and right short sides is a measure of the degree of drift in the immersion nozzle.

Figure 4(a) shows the results of investigating the relationship between the blowing gauge pressure and the hot water level difference on both the left and right short sides using A'' as the blowing gas.When the gauge pressure is 1 kg/cm
``If it is less than 4kg/cm, the flow will be biased towards the blowing side.''
If the water is turned over, the flow will be diverted to the opposite side of the blower, and in either case, the difference in hot water level will become larger.

Figure 4 (b) shows the relationship between the Ar blowing memorial service and the scene level difference on the short side of the left mold.
If it is less than n, uniform blowing will not be possible and the flow will be biased toward the blowing side, and if it exceeds 101/win, the scene variation within the mold will increase and the flow will be biased toward the opposite side of the blowing.

From the results in Figures 4(a) and (g)), the gas blowing gauge pressure was set in the range of 1 kg/cm" to 4 kg/cm", and the gas blowing flow rate was 51/5in-101/
(2) If it is shifted to the in range, the center of the molten steel flow can be controlled to be approximately centered on the nozzle. In this case, fluctuations in the scene due to drifting flow are reduced, and defects in the slab are almost eliminated.

(Example) In continuous casting under the conditions shown in Table 1 above, Ar
Gas blowing (flow 1: 7 f/win, pressure crab 3.
5kg/c+e”G) to investigate the scene level difference between the left and right short sides of the mold and the total oxygen content (hereinafter abbreviated as T-(0)), and also The uneven distribution index of inclusions in the piece and the product surface defect occurrence index shown in equation (2) were investigated.

(However, in the case of Ar injection from the left side) Product surface defect occurrence index Product total rolling amount (Comparative example) Continuous casting was performed in the same manner as in the example except that Ar gas injection was not performed.

FIG. 5 is a diagram illustrating the degree of uneven distribution of T-(0) in the long side direction of the mold in an example and a comparative example.

In the example (・), the T-(0) on the short side of the left and right molds is almost the same, whereas in the comparative example (○), the T-(0) on the short side of the right mold is the same on the short side of the left mold. It's higher.

FIG. 6 is a diagram showing a comparison of the inclusion uneven distribution index indicating the degree of uneven distribution of inclusions in the long side direction of the mold.

The degree of uneven distribution of inclusions in the example is reduced to about 1/4 of that in the comparative example.

From the above results, by carrying out the method of the present invention, drifting in the immersed nozzle is prevented, the difference in flow rate between the left and right discharge ports of the immersed nozzle is eliminated, and the fluctuation in the scene level difference between the short sides of the left and right molds is eliminated. It can be seen that homogeneous slabs with no material deviation can be manufactured.

FIG. 7 is a diagram illustrating product surface defect occurrence index in comparison between Examples and Comparative Examples.

It can be seen that product surface defects due to inclusions, scene variations and powder entrainment are significantly reduced by implementing the method of the invention.

(Effects of the Invention) According to the method of the present invention, it is possible to prevent the drift of molten steel in the submerged nozzle that inevitably occurs in the hot water supply method using a sliding gate, and the difference in flow rate from the left and right discharge ports is eliminated. As a result, uneven distribution of inclusions, powder entrainment,
Scene fluctuations are eliminated, slab quality is improved, and product surface defects can be significantly reduced.

It goes without saying that the method of the present invention is applicable not only to continuous casting of steel but also to continuous casting of all metals.

[Brief explanation of drawings]

Fig. 1 is a diagram schematically showing the longitudinal cross section and molten steel flow of a conventional sliding gate type water heater, and Fig. 2 (a) is a longitudinal cross section of the main part of the water heater used in the method of the present invention and the molten steel flow. Figure 2 Φ) schematically shows A in Figure 2 (a).
-A sectional view, Figure 3 is a diagram explaining the flow velocity of molten steel from the left and right discharge holes of the immersion nozzle and the fluctuation of the scene, (a) is a schematic diagram of the vicinity of the nozzle, and (b) is a diagram of the flow velocity of the discharge flow. Transition, (C)
indicates the transition of hot water level fluctuation. Figure 4 (a) shows the difference in the level of the molten metal on both the left and right short sides of the mold and the A
Figure 4(b) is a diagram showing the relationship between r blow gauge pressure, Figure 4(b) is a diagram showing the relationship with the same <Ar blowing flow rate, and Figure 5 is a diagram showing the degree of uneven distribution of T-(01 in the long side direction of the mold). Figure 6 is a diagram comparing the example and comparative example. Figure 6 is a diagram comparing the inclusion uneven distribution index between the example and the comparative example. Figure 7 is a diagram comparing the product surface defect occurrence index with the example. This is a diagram showing a comparison of examples.

Claims (1)

[Claims] (1) A continuous casting method using a sliding gate and an immersion nozzle, in which hot water is supplied through a porous refractory attached to the inner wall surface of the slider extrusion side at the upper part of the inner hole of the immersion nozzle. , a hot water supply method characterized by blowing gas and suppressing uneven flow of the injection flow. (2) The hot water supply method according to claim 1, characterized in that the gas blowing gauge pressure is in the range of 1 to 4 kg/cm^2 and the blowing flow rate is in the range of 5 to 10 l/min. (3) The installation range of the porous refractory is 50 mm or more in the longitudinal direction from the upper end of the inner hole of the immersion nozzle, and the horizontal cross-sectional area of the injection hole of the porous refractory attachment part is 60 to 80 mm of the horizontal cross-sectional area of the straight body of the immersion nozzle. %. The hot water supply method according to claim 1 or 2, characterized in that a submerged nozzle is used. (4) An immersed nozzle with a porous refractory attached; the shape and horizontal cross-sectional area of the injection hole are equal to the shape and horizontal cross-sectional area of the outlet hole of the lower fixed plate of the sliding gate; ) to (3).