JPS63188462A - Continuous casting method - Google Patents

Abstract

PURPOSE:To reduce trouble at the time of casting by arranging a partition plate between a submerged nozzle and a mold wall in the mold and executing the casting while supplying low viscous powder in the inside thereof and high viscous powder in the outside thereof. CONSTITUTION:The partition plate 4 is arranged between the submerged nozzle 1 of a tundish and the water cooled mold 3 and in the inside, the low viscous powder 5 having good inclusion removing property is charged. Further, in the outside, while charging the high viscous powder 6 improving lubricity between the molten steel 11 and the mold 3 wall, the casting is executed. As the low viscous and the high viscous powders 5, 6 are supplied in the inside and the outside by arranging the partition plate 4, the flowing of the powder is uniformized and slag film 7 having good lubricity is formed. In this way, cleanliness of the cast slab is obtd. and the development of the casting trouble of breakout, etc., is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for continuously supplying powder into a mold in continuous casting of molten metal.

BACKGROUND OF THE INVENTION Since the properties of slabs manufactured by continuous casting affect the quality and yield of the final product, the manufacturing method is an important technical point. Therefore, currently, powder is added to prevent oxidation of the molten steel in the mold, absorb non-metallic inclusions in the molten steel, or improve the lubricity between the molten steel and the mold in order to improve the quality of the slab.

In other words, powder in continuous casting is used to prevent restraint breakout and slab surface defects (vertical cracks, wrinkles), to provide a lubricant between the molten steel and the mold, to prevent oxidation of the molten steel, and to prevent oxidation of the molten steel. Properties such as inclusion absorption are required.To achieve this, the powder properties must be to ensure an appropriate thickness of the molten powder pool and proper flow after melting (appropriate uniform flow between the molten steel and the mold and ensure a film thickness). is necessary.

The thickness of this molten powder pool is easily affected by casting conditions, especially casting speed and oscillation conditions, but if the powder thickness is insufficient, the molten powder will not flow between the mold and the molten steel, resulting in longitudinal cracking of the slab. induce occurrence. Furthermore, if the thickness of the molten powder becomes extremely excessive, bareness or skinning may occur, which is not desirable.

For these reasons, in the case of high carbon steel, a powder thickness of about 6 to 10 mm and a powder viscosity of about 2.0 pige are preferable without causing vertical cracks. On the other hand, the suitable flow conditions for the latter powder are determined by the viscosity after melting, and the appropriate range is greatly influenced by temperature fluctuations in the mold, but it also changes depending on the amount of inclusions that float up and absorb from the molten steel. When All 203 inclusions are absorbed,
It is observed that the powder composition changes and the viscosity tends to increase.

Therefore, if a large amount of M2O3-based inclusions are expected to be absorbed, the appropriate powder viscosity range should be set to a lower value of 1 to 2 poi.
se (at 1300° C.), a good condition can be maintained.

In addition, if high viscosity powder of 2 poise or more is added at the early stage of casting, the molten steel will cool rapidly and will not melt completely, resulting in insufficient lubrication between the molten steel and the mold, resulting in vertical cracks and wrinkles on the surface of the slab. In addition to this, non-metallic inclusions are generated on the surface layer of the slab by being caught up in the molten steel flow, resulting in quality deterioration.
In order to solve these problems, the following conventional techniques are known.

Japanese Patent Publication No. 59-37711 proposes a method for controlling the flow of molten steel with a jammer plate installed in the direction of the narrow wall between the immersion nozzles and preventing powder from being entrained. The main purpose is to control the discharge flow from the immersion nozzle.

Furthermore, in JP-A No. 80-221156, the lubrication of the slab in the mold is improved by opening distributed pores in the mold face plate and supplying lubricant directly between the face plate and the slab shell through these pores. , presents a method to obtain slabs with excellent surface quality.

Problems to be Solved by the Invention As mentioned above, in terms of the required characteristics of powder for molding, a powder with a high viscosity of about 2 to 3 poise is best in terms of lubricity between the molten steel and the mold, but powder inclusions A powder with a low viscosity of about 0.5 to 1.5 poise is desired for its absorption function. Although conflicting powder properties are required in this way, the current situation is to appropriately balance these conflicting required properties using the same type of powder, and then select and use a brand with the properties that match it. be.

Means for Solving the Problems The present inventor has invented a method of using a lubricating powder and an inclusion absorbing powder in combination to make the powder characteristics function effectively. That is, a partition plate is installed between the immersion nozzle in the mold and the mold wall, and the inside of the partition wall has a pressure of 0.5 to 1.5 poise.
Mainly by supplying low viscosity powder of
, 03 system inclusions are absorbed, and at the same time, 2
Appropriate amounts of high viscosity powder of about ~3 polse are supplied at a time to improve the lubricity between the molten steel and the mold, thereby preventing restraint breakout, longitudinal cracking of the slab, wrinkles, and scratches.

Next, the powder charging method of the present invention will be explained based on FIG. 1. The molten steel in the tundish shown in Fig. 1 passes through the immersion nozzle 1 and is cast into the mold 3 while the flow rate is controlled by the nozzle stopper. At this time, a partition plate 4 is provided between the immersion nozzle 1 in the mold and the mold 3. Continuous casting is carried out while simultaneously charging a low-viscosity powder 5, which is good at removing inclusions, into the inside, and a high-viscosity powder 6, which improves the lubricity between the molten steel and the mold wall, to the outside.

As a result, powder viscosity sufficient to absorb inclusions can be obtained on the inside of the partition plate, and an appropriate thickness of powder between the molten steel and the slab is ensured on the outside of the partition plate, resulting in uniform inflow and improved lubrication. A good slag film 7 is formed.

Example Examples will be described below.

(1) Prerequisites (1) Steel type; 5WRH72A (2) Molten steel temperature: 1B00℃ (3) Maximum molten steel processing 11; 180 tons (2) Equipment specifications (1) Continuous casting machine; vertical type (2) Tundish; 12E ( 3) Mold shape; 400mm x 25Os layer angle (
4) Partition plate shape: 270m x 180mm square (3)
Table 1 shows the types of powders used in the present invention.

(4) As a result, after installing the partition plate inside the mold,
20. A cast slab produced by the method of the present invention in which 0.7 poise low viscosity powder with good adsorption properties for system inclusions is added and at the same time 2 poise high viscosity powder considering lubricity is added to the outside of the partition plate and the conventional method. We compared the surface quality and internal cleanliness of the slabs produced in the following manner. We also compared the occurrence of breakouts.

First, looking at the surface quality, as shown in Table 2, in the method of the present invention, vertical cracks on the surface of the slab are not observed, whereas in the conventional method, the molten steel temperature in the tundish is high. Cracks are observed.

Further, breakout did not occur at all in the present invention, whereas breakout occurred in some cases in the conventional method.

Next, the internal quality of the slabs manufactured by the present invention and the conventional method was cleaned using At
, 03 series inclusion index was compared. Here, the inclusion index is the average length on the major axis side of All, 03 type inclusions.
Therefore, as shown in FIG. 2 and Table 2, the inclusion index of the present invention was significantly smaller than that of the conventional slab, and a high level of cleanliness was achieved.

(Left below) Effects of the Invention According to the present invention, high cleanliness of slabs can be achieved in continuous casting, and operational troubles such as breakouts can be reduced. The industrial value is very high.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a powder charging device according to the present invention, FIG. 1 (1) is an elevation view, and FIG. 1 (2) is a plan view. FIG. 2 is a diagram showing test results in Examples. l... Immersion nozzle, 3... Water-cooled mold (mold). 4... Partition plate, 5... Low viscosity powder, 6... High viscosity powder, 7... Slag°, film, 9...
Slag calendar, lO... solidified shell, 11... molten steel,
12...Slugbear (string). Agent Patent Attorney Masaru Inoue

Claims (1)

[Claims] In the continuous casting method for molten metal, a partition plate is installed between the immersion nozzle in the mold and the mold wall, and a low-viscosity powder with good inclusion adsorption properties is injected into the inside of the partition plate, and at the same time, the molten steel outside the partition plate and the mold are injected. A continuous casting method that is characterized by continuous casting while supplying highly viscous powder with excellent lubricity between the walls.