JPH02207955A - Method for detecting drift stream of molten steel in mold at the time of continuously casting - Google Patents

Abstract

PURPOSE:To detect drift stream of molten steel in a mold and to reduce content of non-metallic inclusion in continuous cast slab by obtaining difference of conductive heat quantities of cooling water at both short sides of the mold at the time of pouring the molten steel into the mold for continuous casting with a submerged nozzle. CONSTITUTION:At the time of pouring the molten steel into the mold in a continuous casting apparatus with the submerged nozzle 2, molten steel discharging holes 3A, 3B in the submerged nozzle 2 are arranged toward both short sides 1A, 1B of the mold. Further, in both short short sides 1A, 1B of the mold, inlets 5A, 5B and outlets 6A, 6B for cooling water are arranged, respectively, to cool the short sides 1A, 1B of the mold. When the hole diameter of the discharging hole 3A comes to small by sticking of the non-metallic inclusion, such as alumina, more quantity of the molten steel from the discharging hole 3B flows out into the mold in priority and the conductive heat quantity at the short side 1B of the mold comes to more than that at the short side 1A. This is obtd. with temp. difference at the inlets and outlets for cooling water and the drift stream degree of the molten steel in the mold, that is the content of the non-metallic inclusion of alumina, etc., in the molten steel, is decided according to the difference and by eliminating the drift stream of the molten steel, the non-metallic inclusion quantity in the continuous cast slab is reduced and the quality is improved.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a method for detecting the drift of molten steel in a mold during continuous casting. This invention relates to a method for detecting drift in a flow.

<Prior art> In general, non-metallic inclusions in molten steel during continuous casting are carried into the slab by the injection flow of molten steel, and most of them float to the surface, while the remaining part remains inside the slab. is captured as is. It is known that the amount of nonmetallic inclusions that are trapped varies greatly depending on the flow of molten steel in the slab during pouring. I see, there is a tendency to increase.

Therefore, in continuous casting, in order to prevent the molten steel flow discharged from the immersion nozzle from reaching deep into the slab, the immersion nozzle is shaped to have a discharge hole on the side toward both short sides of the mold. The discharge hole is used so as to face slightly downward so as not to involve the surface coating flux floating on the t'atlA surface.

In a normal continuous slab caster, the submerged nozzle is placed in the center of the mold with its discharge hole directed toward the short side of the mold, and the tgtlA stream discharged from the discharge hole flows through the molten steel stored in the mold. The velocity of the flow decreases, and the flow becomes reversed due to collision with the short side wall of the mold. One side of this reversal flow becomes an upward flow toward the surface, and the other becomes a downward flow, and as a result of being greatly decelerated during this time, the upward flow does not involve the flux on the surface of the hot water in the vortex. Furthermore, casting is performed to improve the quality of the slab by preventing the downward flow from reaching deep into the slab.

However, if the molten steel flow from the re-discharge hole of the immersion nozzle is uniform, there is no problem, but the flow of molten steel descending through the immersion nozzle may fluctuate depending on the throttle opening of the sliding nozzle on the immersion nozzle, the casting speed, etc. If non-metallic inclusions such as alumina increase on the inner wall of the immersion nozzle, the uniform relationship between the discharge holes will be disrupted, and the flow of molten steel from one of the discharge holes will become stronger, resulting in so-called uneven flow. will occur.

When this drift occurs, the upward flow or downward flow of the molten steel flow in the mold becomes stronger on the side where the strong flow occurs, resulting in flux entrainment or deterioration of internal quality due to the downward flow reaching deep inside the slab. arise. Therefore, detecting the flow state of molten steel in the mold is one of the important factors in improving the quality of cast slabs and the like.

Conventionally, as a method for detecting the occurrence of such a drift in the molten steel flow, an eddy current level meter has been installed between a submerged nozzle and each piece of the mold, as disclosed in Japanese Patent Laid-Open No. 62-197255. A method has been proposed in which two of these are arranged and drift is detected from the deviation of their level values.

<Problem to be solved by the invention> However, installing the eddy current level meter on the short side not only makes it difficult to operate and handle;
There is a problem in that installing an eddy current level meter separately for control increases equipment costs.

An object of the present invention is to provide a method for detecting drifting of molten steel in a mold during continuous casting, which solves the above-mentioned problems.

<Means for Solving the Problems> The present invention is a method for detecting drifting of molten steel in a mold during continuous casting, in which the inlet temperature and the outlet temperature of cooling water for cooling both short sides of the mold are determined. Measure each, find the temperature difference between the inlet temperature measurement value and the outlet temperature measurement value on both short pieces,
The purpose is to achieve the above object by detecting the drift of the molten steel flow in the mold based on the temperature difference.

Note that the temperature difference may be a difference in the amount of heat removed.

<Function> The principle of the present invention will be explained below using FIG. 1.

As shown in the figure, the immersion nozzle 2 is arranged at the center of the mold 1, and its discharge holes 3A and 3B are connected to both short pieces I of the mold 1, respectively.
They are symmetrically provided facing the A and IB sides, and the molten steel flow discharged from the discharge holes 3A and 3B flows out equally in the directions of arrows F and G, and a slab 4 is cast. In addition, the cooling water for cooling the short pieces IA and IB is supplied through supply pipes 5A and 5B at temperatures Ta+ (''C) and T□ (°C), respectively.
), and the temperature Taa (
”c).

The cooling water flow fi V a (It
/a+in)Vm (j!/a+in) is the same (VA
-Vm).

Now, suppose that the adhesion of non-metallic inclusions such as aluminum to the discharge hole 3A side increases and a clogging phenomenon occurs, and molten steel preferentially flows out from the discharge hole 3B side. Since hot TG steel will always be supplied, short piece I
The amount of heat removed from the B side is large.

That is, the temperature difference ΔT of the cooling water on the short piece IB side at this time
m (-Ts.-T, ri is the temperature difference ΔTA of the short piece IA
(-TA-Tag). From this, by comparing these temperature differences ΔTa and ΔTm using the following equation (1), the short piece IA can be calculated.

It is possible to determine in which part of the IB the molten steel flow is drifting.

ΔTl−ΔT, -ΔTA −・−・−・−・
- (1) Therefore, when the adhesion of non-metallic inclusions 6 increases on the discharge hole 3A side and a clogging phenomenon occurs, (11
The temperature difference ΔT shown by the formula and the number of surface blowholes LA (pcs/rrf) on the short pieces IA and IB sides detected after scarfing of the slab after continuous casting, L,
When we investigated the relationship between the difference ΔL (-Ll -L, ) and (pieces/bo), we obtained the results shown in Figure 2.

As can be seen from this figure, the difference in the number of surface blowholes ΔL
There is a good correlation between the temperature difference ΔT of the cooling water between the short pieces IA and IB, and the cooling water temperature difference ΔT. In other words, if there is a drift of the molten steel flow on the short piece IB side, the discharge speed will apparently increase, so it will be blown from the submerged nozzle, and non-metallic inclusions such as gas bubbles and alumina will be drawn in, causing the flow of the molten steel on the short piece IB side. The surface quality of the slab deteriorates.

In addition, in the above explanation, the cooling water for both short pieces IA and IB! IV
Although it is assumed that x and Vm are equal, the present invention is not limited to this, and even if the two are different, the temperature of one short piece, for example ΔT, can be corrected by setting ΔT, · (Vl/VA). A similar relationship can be found by

In addition, here, the value of the temperature difference ΔT was used to find out the difference ΔL in the number of surface blowholes, but instead of this ΔT,
Amount of heat removed from both short pieces IA and IB Q^.

Qm (kcai, / nl ・h) is expressed as (2) below,
(3), and the difference in heat removal ΔQ is (4
) It goes without saying that a similar relationship can be obtained by using the equation.

QA-ΔTA' Wb ・C/SA −・
(2) Qs = ΔT, ・W, −C/S, ・・・・・・−
----1... (3) Here, WA, W, cooling water flow rate of short pieces IA, IB (kg/h); surface area of short pieces IA, IB (nf); specific heat of cooling water (kca 1 / kg・”C)-Q,
-...-(4) S^, SI ΔQ-Q.

<Example> [Example 1] A slab with a size of thickness: 260 nn x width: 1200 mm was poured at a speed of 7.5 m at 1.3 m/sin.
The length of was cast to obtain a test material L, and then 50 mm was cast under the same conditions.
A length of 0 m was cast to obtain sample material 2. Table 1 shows the measurement results of the temperature difference of the cooling water during casting and the number of blowholes on the surface of the slab after scarfing.

Table 1 After the casting of sample material 2 was completed, the casting was interrupted and the immersion nozzle was observed. As a result, a clogging phenomenon was observed in the discharge hole 3A on the short piece IA side shown in Fig. 1 above, and the blockage rate ( The ratio of the blocked area to the total area of the discharge holes was 28%.

In addition, the blockage rate of the discharge hole 3B on the short piece 1B side at this time is 5.
%Met.

As can be seen from Table 1, the number of blowholes in a non-clogged state is approximately 1/rrr, so even if the discharge hole 3A side is blocked and the molten steel flow is concentrated on the discharge hole 3B side, The total number of both blowholes on the slab surface should be assumed to be approximately 2/po. but,
In reality, this table shows that when the molten steel flow on the discharge hole 3B side increases, the defects that occur due to this increase exponentially with the rate of increase in the discharge flow, resulting in very bad results. There is.

[Example ■]

Cooling water temperature difference ΔT between both short pieces in continuous casting is 0.5
Thickness below °C = 260 bites x width: 1000-1350
Throughput by body size: 3.5-4. OL/bi
Sample material 3 is 25 slabs of n, and the temperature difference ΔT is 2.5.
~3°5°C Thickness: 260mmX Width: 1010~1
Throughput at 380mm size: 3-5~4. OL
Twelve slabs of /win were used as sample material 4, and after hot rolling, they were subjected to pickling treatment and checked for defects.

As a result, the coil defect length defect rate of sample material 3 was 3 on average.
．． It was 8%, but in the case of sample material 4, it was 12.4%, and among them, two coils with 10% or more occurred and were downgraded.

<Effects of the Invention> As explained above, according to the present invention, it is only necessary to use the temperature difference of the existing mold cooling water, so it is possible to easily and inexpensively detect the drift of the molten steel flow in the mold. . Furthermore, this makes it easier to determine product quality, which can contribute to improving product yield.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the principle of the present invention, and FIG. 2 is a characteristic diagram showing the relationship between the temperature difference in the cooling water of both mold strips and the difference in the number of blowholes on the surface of the slab. l...; mold, IA, IB... short piece, 2... immersion nozzle, 3... discharge hole, 4... slab,
5... Supply pipe, 6... Discharge pipe. Patent applicant: Kawasaki Steel Corporation

Claims (1)

[Claims] 1. A method for detecting drifting of molten steel in a mold during continuous casting, which measures the inlet and outlet temperatures of cooling water that cools both short sides of the mold, and A method of uneven flow of molten steel in a mold during continuous casting, characterized by determining the temperature difference between an inlet temperature measurement value and an outlet temperature measurement value of a short piece, and detecting the uneven flow of molten steel in the mold based on the temperature difference. Detection method. 2. The method for detecting drifting of molten steel in a mold during continuous casting according to claim 1, wherein the temperature difference is a difference in amount of heat removed.