JPS6137358A - Continuous casting method - Google Patents

Abstract

PURPOSE:To obtain a billet having good quality with less intrusion by controlling the fluctuation of a molten metal surface in a prescribed range and maintaining the clogging of a tundish nozzle in a prescribed range or below. CONSTITUTION:The molten metal 1 poured into a tundish 2 is poured into a mold 7 through an immersion nozzle 6. The level of the molten metal is detected by a mold level gage 8 and the fluctuation of the molten metal level in the mold is maintained at the prescribed value. The clogging index of the tundish nozzle is calculated from the opening degree of a sliding nozzle 5, casting speed, height (h) of a tundish head, etc. and is maintained at the prescribed value. The intrusion of inclusions is thus decreased and the fraction defective of the quality of a billet is decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention is an object of the present invention to control the fluctuation of the melt level within a predetermined range in continuous casting, and to maintain the tundice nozzle clogging within a predetermined range. This invention relates to a continuous casting method for obtaining slabs of good quality with less entrainment.

(Prior Art) The continuous casting method is a method of continuously casting slabs by injecting molten metal from a ladle into a tundish, and then from the tundish into a mold via a submerged nozzle.

In order to prevent breakouts caused by fluctuations in the mold level and deterioration of slab quality due to the inclusion of inclusions,
Conventionally, a device has been used that detects the distance to the mold hot water surface by, for example, reflection of electromagnetic waves and keeps the mold hot water level constant (Japanese Utility Model Publication No. 53-38647).

In addition, since there is a correlation between tundish nozzle clogging and slab quality, there is a proposal for a nozzle that does not accumulate alumina, which is the main cause of nozzle clogging (Japanese Patent Laid-Open No. 57-27
967, patent application No. 55-98508).

However, in order to obtain good slab quality, controlling the fluctuations in the melt level alone is not sufficient. Even when the fluctuations in the hot water level are small,
When there is a tendency for tandishy nozzle clogging, the quality of the slab deteriorates. This is because inclusions mainly composed of alumina that have adhered and deposited inside the picks and nozzles sometimes flow out into the mold and remain caught up in the slab.

Furthermore, even if the condition of the tandishy nozzle plugging is the same, if the melt level fluctuation is large, the quality of the slab will be the worst, and if the melt level fluctuation is small, the quality will be relatively only slightly deteriorated. Therefore, it is difficult to uniformly predict the quality based on the state of clogging of a certain tundish nozzle.

Conventional methods of controlling only the fluctuation of the melt level or predicting the quality of slabs based only on the clogging of the tandishy nozzle were insufficient for casting slabs of good quality.

(Problems to be Solved by the Invention) The purpose of the present invention is to solve the above-mentioned drawbacks and to present a continuous casting method for casting slabs of good quality and containing alumina as a main component with few inclusions. do.

(Means for Solving the Problems) In order to achieve the above object, the present invention controls the mold level to within a predetermined range, and continuously pumps the molten metal while maintaining the tundish nozzle clogging within a predetermined range. This method is characterized by casting.

(Actions of the Invention) The effects that led the present inventors to recognize the above-mentioned configuration of the present invention as essential will be specifically described based on the results of experiments that revealed the effects. As a comparative example, an experiment was conducted using a casting method in which only the molten metal level was controlled and the tundish nozzle filling was not controlled, and a method of controlling both was conducted. The steel types used in the experiment were two types with different Ω levels ([Aj = 0.
011chi), ■([w) = o, o 64%). In either case, the mold level is controlled so that its fluctuation range is within 10wn, and in the method of controlling both, the tundish nozzle clogging index 9 (see formula 0 below) is controlled to be 90% or less. When the Mendisch nozzle clogging index returns to 100%, the gas flow rate from the upper nozzle is increased by 10 nozzles per minute. Casting was carried out to maintain the above. Table 1 shows a comparison between the experimental method and a comparative example, using the results as an indicator of the rate of defective quality of slabs caused by alumina.

H].

For @species ■, the quality defect rate was 0% when the mold level fluctuation was 10 degrees or less and the Tandishy nozzle clogging index was 92 degrees or more. In addition, for steel type (1), the quality defect rate was 0 when the mold level fluctuation was 9 mm or less and the tandy sea nozzle clogging index was 90% or more.

From these results, it can be seen that the range of fluid level fluctuation and the predetermined range of tundish nozzle clogging υ to avoid quality defects vary depending on the steel type.

It is thought that alumina exists in two places: one attached to the immersion nozzle and the other in the mold powder.

Therefore, in order to prevent alumina from being drawn in, the mold powder level fluctuations should be controlled within a range of 10 or less to prevent mold powder from being drawn in, and the nozzle clogging should be kept within a nozzle clogging index of 90% or more. It was discovered that alumina adhesion inside the nozzle could be minimized by maintaining the alumina at a constant temperature.

The control situation at this time is shown in FIGS. 2 and 3. FIG. 2 shows the experimental method, and FIG. 3 shows the comparative example. As shown in Fig. 2, the experimental method was to use a hot water level meter 9 to control mold hot water level fluctuations within, for example, 10 degrees, and to maintain the tundish nozzle filling within a predetermined range. When the dish nozzle clogging index falls below a certain value (a in Figure 2), the gas flow rate from the upper nozzle is increased through piping 4 until it rises to a predetermined value (b in Figure 2), and the gas flow rate inside the nozzle is increased. Casting was carried out after removing the deposits and eliminating the nozzle clogging, and in the comparative example, casting continued as soon as the nozzle clogging was controlled.

(Example) FIG. 1 shows an apparatus used in an embodiment of the present invention.

In Figure 1, the melt &1 injected into Tandisi-2
is injected into the mold 7 through the immersion nozzle 6,
The mold level meter 8 detected the hot water level. As is well known, the scene level can be detected using thermocouples, ultrasonic waves, radiation, etc., and any of these methods can be used in the present invention.

In addition, Kundissi = nozzle clogging index was calculated using the formula 0 from the opening casting of the sliding nozzle 5: A degree, the Kundissi head height hl, etc.

(Tandishy nozzle clogging) index - (Actual flow rate) / (Theoretical flow rate) S Nisliding nozzle opening area, g: Acceleration of gravity, h: Tandishy head height A
For no-si-killed steel (Cy = 0.011chi), 1) When the method of the present invention is implemented (mold level fluctuation 10 times or less, tundish clogged! finger i? (t9
2), as a comparative example, 11) Implement only the mold level control (mold level level variation is 10wn or less), 1ii) Implement only the control of the tundish nozzle uh (tandish nozzle clogging index of 92% or more) , lv) The quality failure rate of slabs caused by alumina was compared in four cases: both the melt level and Tandishy nozzle clogging were not controlled.

The results are shown in FIG. 4 (the numbers in the box indicate the quality defect rate. The quality defect rate is 10%, 16%, and 41%, respectively, but in the example of the method of the present invention, the quality defect rate was 0%.

(Effects of the Invention) The present invention operates by controlling mold level/bell control and nozzle clogging within a range that produces a synergistic effect, so entrainment of inclusions whose main component is alumina is reduced. The effects are significant, such as being able to significantly reduce the quality defect rate of slabs and significantly improving the integrated yield from steel manufacturing to finished products.

[Brief explanation of the drawing]

FIG. 1 is a side sectional view of the device used in the example of the present invention, FIGS. 2 and 3 are diagrams explaining the control situation of the experimental example and comparative example of the present invention, and FIG. FIG. 3 is a diagram showing the results of an example of the invention. 1...Molten metal 2...Tandish 3.
... Upper nozzle 4 ... Gas blowing pipe 5 ... Sliding nozzle 6 ... Immersion nozzle 7 ... Mold 8 ... Mold level meter 9 ... Calculator h ... To the tundish, do height Figure 1 Figure 2

Claims (1)

[Claims] A continuous casting method characterized by casting molten metal while controlling the mold surface level within a predetermined range and maintaining tundish nozzle clogging within a predetermined range.