JPH10193065A - Detection of depression in vertical direction of solidified shell in mold in continuous casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect the depression in the longitudinal direction and to predict the breakout caused by breakage of solidified shell by continuously measuring the temp. of inner surface of a mold over on the whole periphery and indicating downward peak wave form rapidly lowered and raised in the measured temp. curve at a prescribed position with time. SOLUTION: The solidified shell 100 is locally shrunk with uneven flow, etc., of mold powder into the inner surface of the mold 102 to develop the recessed part 104 and the air gap 106 between the mold 102 and the solidified shell 100 is developed to develop the delay of solidification. In the case this condition continuously succeds, a prescribed length of recessed part and depression are developed in the longitudinal direction on the solidified shell 100, and the longitudinal crack is developed with the shrinkage accompanied with the surrounding shrinkage, and the solidified shell 100 is broken at a position taken off the lower part from the mold 102 to develop the breakout flowing out molten steel. At the time of developing the depression on the solidified shell 100, the temp. is rapidly lowered with the air gap 106 and reversely, at the time of bringing the normal solidified shell into contact with the inner surface of the mold, the temp. is raised.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a vertical depression of a solidified shell in which a part of the solidified shell is dented and deformed over a predetermined length in a mold during continuous casting.

[0002]

2. Description of the Related Art Continuous casting has been widely practiced in which molten steel is continuously poured into a mold and a solidified shell formed in the mold by cooling is continuously drawn downward to perform casting. I have. During this continuous casting, a breakout in which the solidified shell is partially broken in the mold for some reason and the molten steel flows out when the broken portion escapes downward from the mold has conventionally been a major problem. This breakout can occur for a variety of reasons, one of which is breakout due to solidified shell depletion.

Here, the depression of the solidified shell is
As shown in the plan view of FIG. 4, this is a phenomenon in which a part of the solidified shell 100 in the circumferential direction is dented and deformed vertically toward the center of the solidified shell over a predetermined length. For example, due to uneven flow of mold powder into the inner surface of the mold 102, the solidified shell 100
Is locally contracted and deformed into the center of the solidified shell 100. When such a dent 104 occurs, the air gap 1 between the mold 102 and the solidified shell 100 is reduced.
06 is caused and a solidification delay is caused in the portion. If the solidification delay continues, a depression (depression) of a predetermined length is generated in the solidified shell 100 in the longitudinal direction, and a depressed portion is formed by a tensile force at the time of contraction caused by solidification in the periphery. Small vertical cracks occur When the vertical cracks are gradually increased, the solidified shell 100 is broken when the mold 102 is pulled downward, causing a breakout in which the molten steel flows out to the outside.

Further, even if such a breakout does not occur, a vertical crack 110 (having a length of 15 mm in the illustrated example) is formed in the surface layer of the solidified shell 100, that is, the slab 108 (see FIG. 5).
0 mm) remains, causing problems such as grain boundary cracks starting from the vertical cracks 110 in the subsequent rolling process, or such vertical cracks 110 remain in the product steel and become defective parts. This creates a problem of becoming dull.

[0005]

SUMMARY OF THE INVENTION The method for detecting vertical depression according to the present invention has been created to solve such a problem. According to the detection method of the present invention, in the continuous casting, a part of the solidified shell in the circumferential direction inside the mold is vertically depressed to a center side of the solidified shell from the inner surface of the mold over a predetermined length. This is a method of detecting vertical depletion, in which the temperature of the inner surface of the mold is continuously measured over the entire circumference, and the measured temperature curve at a predetermined measurement site sharply decreases with time and then sharply increases again. The generation of the vertical direction depression is detected by showing a downward peak waveform of the form.

According to a second aspect of the present invention, in the first aspect, a plurality of thermocouples are embedded in the mold near the inner surface of the mold and over the entire circumference, and the thermocouples are used to detect the temperature of each part of the inner surface of the mold. It is characterized by performing measurement.

[0007]

[Function and Effect of the Invention] In the case of a general breakout,
In other words, in the case of a breakout in which the solidified shell breaks in the mold and the molten steel inside the solidified shell is exposed directly to the inner surface of the mold, the temperature of the inner surface of the mold rises sharply due to the contact with the high-temperature molten steel. Then, a phenomenon of descending due to the formation of the secondary shell occurs.

[0008] On the other hand, when the above-mentioned depletion occurs, the present inventor has found that the temperature of the inner surface of the mold at the site where the depletion is generated tends to suddenly decrease and then rapidly increase. As a result of research, it turned out. This is based on the following reasons.

That is, when such depletion occurs in the solidified shell, the temperature of a predetermined portion of the inner surface of the mold, that is, a portion corresponding to the depletion, partially drops due to an air gap between the inner surface of the mold and the solidified shell. Then, when such depletion passes and the inner surface of the mold comes into direct contact with a normal solidified shell without an air gap, the temperature of the inner surface of the mold at the predetermined portion starts to rise.

Therefore, the above-mentioned depletion can be detected when the temperature of the inner surface of the mold is continuously measured and the measured temperature curve shows a downward peak waveform. The present invention has been made based on such knowledge.

According to the present invention, the breakout caused by the depression can be predicted in advance,
It is possible to prevent such a breakout from occurring. Alternatively, the information can be fed forward to a subsequent rolling process or the like to facilitate flaw removal,
It is possible to prevent intergranular cracks caused by rolling or to prevent defects in the product steel material from remaining.

In the present invention, a plurality of temperature sensors can be embedded near the inner surface of the mold and over the entire circumference, and the temperature sensors can measure the temperature of each part of the inner surface of the mold. By doing so, the temperature of each part on the inner surface of the mold can be monitored by a simple method. Here, a thermocouple can be suitably used as the temperature sensor (claim 2).

[0013]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention; FIG. 1 shows a continuous casting facility and a continuous casting method. In the figure, reference numeral 10 denotes a tundish, in which molten steel 12 inside is continuously supplied to a lower mold 14.

A cooling water passage is provided inside the mold 14, and the molten steel 12 is cooled by the cooling water flowing through the passage.
Primary cooling is performed. Then, by the cooling, the solidified shell 1 is formed on the outer peripheral portion of the molten steel 12 inside the mold 14.
6 are formed.

Reference numeral 18 denotes a secondary cooling zone, which sprays cooling water from a spray nozzle to cool the molten steel 12 following the mold 14. Reference numeral 20 denotes a drawing roll, and the slab 22 as a solidified body is continuously drawn from the mold 14 by the drawing roll 20.

The mold 14 has a rectangular planar shape, and a thermocouple 24 as a temperature sensor is embedded in a portion near the inner surface thereof in a pattern shown in FIG.

FIG. 2 shows the inner surface of the mold 14 developed right and left. As shown in FIG. 2, in this example, the thermocouples 24 are provided at three places in the circumferential direction for both the long side portion 14A and the short side portion 14B. , And at the same circumferential position in three stages vertically. At the corners of the long side portion 14A, the thermocouples 24 are vertically arranged in four stages.

FIG. 3 shows that the width of the long side portion 14A is 480.
mm, the width of the short side portion 14B is 370 mm, and the height is 60 mm.
It shows a temperature curve obtained when 420 case-hardened steel was continuously cast at a maximum casting speed of 0.70 m / min, and the temperature was measured by the thermocouple 24. However, the vertical axis represents temperature, and the horizontal axis represents time.

FIG. 2 shows a temperature curve measured by a thermocouple 24 at a predetermined position in the circumferential direction during continuous casting. As shown in FIG. The downward peak waveforms P and P ′ appear in the band.

The upper solid line in the figure indicates the uppermost thermocouple 24.
The curve indicated by the broken line on the lower side is the thermocouple 24 at the same position in the circumferential direction,
Respectively show the measurement results obtained by the thermocouple 24 immediately below the.

In these temperature curves, the magnitude of the peak waveforms P and P ′, that is, the temperature drop width is 25 to 35 ° C., and portions other than the downward peak waveforms P and P ′ (S and S in the figure)
S ′) was about 100 ° C. In addition, it was confirmed that the above-described depletion occurred in the portions showing the peak waveforms P and P ′.

In the case of this embodiment, downward peak waveforms P and P 'appear without significant time lag between the uppermost thermocouple 24 and the thermocouple 24 immediately below. This is considered to be due to the fact that the depression occurred almost simultaneously between the upper and lower thermocouples 24.

When depletion occurs with a time lag between the upper and lower thermocouples 24, that is, when the small depletion shifts downward with the passage of time, the upper thermocouple 24 Downward peak waveforms P and P ′ with a time lag between the thermocouple 24 and the lower thermocouple 24.
May appear.

In any case, depletion detection can be performed more accurately by detecting depletion based on the results of temperature measurement by the upper and lower thermocouples 24 at the same position in the circumferential direction. Further, in order to perform accurate depletion detection, it is possible to determine that depletion has occurred when a downward peak waveform having a magnitude exceeding a threshold value appears. At this time, the threshold value can be set to, for example, 10 to 15 ° C. in the temperature decrease width.

According to this embodiment, a breakout caused by the depression can be predicted in advance, and the occurrence of such a breakout can be prevented. Alternatively, the information can be fed forward to a subsequent rolling process, etc., so that flaw removal can be facilitated, thereby preventing grain boundary cracks caused by rolling or preventing defects from remaining in product steel materials. Can be.

Although the embodiment of the present invention has been described in detail, this is merely an example, and the present invention can be implemented in variously modified forms without departing from the gist thereof.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a continuous casting facility and a continuous casting method.

FIG. 2 is a diagram showing an example of an arrangement pattern of thermocouples embedded in a mold of FIG. 2 in FIG. 1;

FIG. 3 is a diagram showing a temperature measurement result of an inner surface of a mold measured by the thermocouple of FIG. 2 and a downward peak waveform appearing therein.

FIG. 4 is an explanatory diagram of depletion which is a detection target of the present invention.

FIG. 5 is a view showing a vertical crack caused by the depression of FIG. 4 together with a slab.

[Description of Signs] 10 tundish 12 molten steel 14 mold 16 solidified shell 24 thermocouple (temperature sensor) P, P 'Downward peak waveform

Claims (2)

[Claims] 1. A method for detecting a longitudinal depression of a solidified shell in which a portion of the solidified shell in the circumferential direction is vertically depressed from the inner surface of the mold toward the center of the solidified shell within a predetermined length within the mold during continuous casting. The temperature of the inner surface of the mold is continuously measured over the entire circumference, and a downward peak waveform of a form in which a measured temperature curve at a predetermined measurement site rapidly decreases with time and then sharply increases again. A method for detecting the longitudinal depression of a solidified shell in a mold in continuous casting, wherein the method includes detecting occurrence of the longitudinal depression. 2. The mold according to claim 1, wherein a plurality of thermocouples are embedded in the mold in the vicinity of the inner surface of the mold and over the entire circumference, and the thermocouples measure the temperature of each part of the inner surface of the mold. A method for detecting longitudinal depression of a solidified shell in a mold in continuous casting.