JPH06262302A - Continuous casting method of stainless steel - Google Patents

Abstract

PURPOSE:To improve the production efficiency without reducing the quality even when the casting speed is increased in the continuous casting of stainless steel. CONSTITUTION:In manufacturing the cast slab of stainless steel by using a continuous casting machine of vertical bending type, a dipping nozzle provided with a discharge port having the angle to be within the range of 5 deg. upward and 35 deg. downward with the direction orthogonal to the nozzle axis as the reference is dipped so as to be 150-300mm deep from the mold meniscus surface of the mold for the continuous casting. In this condition, the molten stainless steel is supplied in the mold, and at the same time, the cast slab of stainless steel is drawn out from the mold at the casting speed of 0.8-1.8m/min.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting method for stainless steel, and particularly, it is effective for deterioration of quality due to inclusion of inclusions which is a concern when performing continuous casting at high speed for this type of steel. It is something to try to avoid.

[0002]

2. Description of the Related Art In continuous casting of stainless steel, a vertical continuous casting machine is generally used. The reason is,
Vertical continuous casting machines are more likely to have inclusions and Ar compared to curved continuous casting machines.
This is because the floating property of gas bubbles is excellent and a high quality slab can be obtained. However, it is difficult to further increase the machine length of this vertical continuous casting machine because it is limited by the height of the building that houses the vertical continuous casting machine. There is a disadvantage that it is difficult to apply to high-speed casting (casting in which cast slabs are pulled out of the mold at high speed).

As a means for realizing high speed casting, a dipping nozzle provided with a nozzle hole having an upward angle of 5 to 15 ° relative to the direction orthogonal to the axis of the nozzle is used. A technique such as disclosed in Japanese Patent Laid-Open No. 55-82277 for continuous casting (forming an upward discharge flow in the molten metal in the mold to reduce stagnation at the top of the molten metal and adsorbing inclusions to the artificial slag It is also possible to apply () to reduce the bite of the molten metal), but when high-speed casting is performed using the immersion nozzle as disclosed here, the discharge of the molten metal flowing out from the immersion nozzle is performed. Since the speed is high, there is a disadvantage that the quality of the cast slab is rather deteriorated by the inclusion of mold powder on the surface of the molten metal in the mold, and it is difficult to say that this is an effective means.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to propose a novel casting method capable of avoiding the deterioration of quality which is a concern when casting a cast stainless steel slab at a high speed.

[0005]

As a continuous casting machine capable of simultaneously satisfying the two needs of improving the quality of steel and improving productivity, a vertical bending type continuous casting machine having a vertical portion and a curved portion is advantageous. The present invention is intended to perform high speed casting of stainless steel using such a continuous casting machine. That is, according to the present invention, when a stainless steel cast slab is manufactured using a vertical bending type continuous casting machine, 5 ° above and 35 ° below the direction orthogonal to the axis of the nozzle as a reference. Immerse a dipping nozzle equipped with a discharge hole with an angle within the range of ° to a depth of 150 to 300 mm from the mold meniscus of the continuous casting mold,
In this state, while supplying molten metal of stainless steel into the mold, a continuous casting method of stainless steel is characterized in that a cast slab of stainless steel is pulled out from the mold at a casting speed of 0.8 to 1.8 m / min. . Here, with respect to the angle of the discharge hole of the immersion nozzle, with respect to the direction orthogonal to the axis of the nozzle as a reference, above and below it refer to the direction orthogonal to the axis L of the nozzle as shown in FIG. (Represented by reference line P)
If it is above it, it is called up, and if it is below it is called down, and the immersion depth of the immersion nozzle is
As shown in FIG. 2, it is defined as the vertical distance d from the upper end of the discharge hole of the immersion nozzle to the mold meniscus.

[0006]

[Operation] When the casting speed is in the range of 1.0 to 1.2 m / min and stainless steel (steel type: SUS 304) is continuously cast, the angle Θ of the discharge hole of the immersion nozzle and the immersion depth d are changed. Fig. 3 shows the results of the investigation on the influence on the quality of the slab. From the figure, the angle Θ of the discharge hole of the immersion nozzle is set in the range of 35 ° (−35 °) downward to 5 ° (+ 5 °) upward, and the immersion depth d is set in the range of 150 to 300 mm for continuous casting. When this is done, the quality defects that occur in the cast slab are extremely small.

Further, the angle Θ of the discharge hole of the immersion nozzle is set to -35.
Fig. 4 shows the results of an investigation on the influence of the quality of the slab when the casting speed v and the immersion depth d were changed in the range of ° to + 5 °. The casting speed v was 0.8 to 1.8 m / min.
By setting the immersion depth d of the nozzle to 150 to 300 mm, quality defects of the cast piece can be reduced. Under these conditions, especially when the immersion depth d of the nozzle is made deeper, the quality of the slab is deteriorated, but this is because the heat supply to the vicinity of the meniscus due to the upward flow of molten steel is reduced, and the powder It is thought that this is because the amount of melt increases and the amount of slag increases.

The present invention is based on the above findings.
From the mold meniscus of the continuous casting mold, a submerged nozzle having a discharge port having an angle of 5 ° above and 35 ° below the direction perpendicular to the axis of the nozzle is 150 It is arranged so that the immersion depth is 300 mm, and in this state the molten metal of stainless steel is supplied into the mold, and the cast slab of stainless steel is cast from the mold at a casting speed of 0.8 to 1.8 m / min. Since it is pulled out, it is possible to effectively avoid the quality defect due to the inclusion of inclusions or the like that occurs when stainless steel is cast at high speed. Further, in the present invention, since a vertical bending type continuous casting machine is used, there are very few restrictions that occur when a vertical type continuous casting machine is used.

As the stainless steel cast according to the present invention, any of ferritic, austenitic, martensitic stainless steel, etc. can be applied.

[0010]

[Example] Stainless steel with a width of 1200 mm and a thickness of 200 mm
In order to manufacture cast slabs of (SUS304), first, lower 35 °
Immersion nozzle with an outlet with an angle of
m, inner diameter 70 mm) was arranged so that the immersion depth was 250 mm from the mold meniscus of the continuous casting mold, the supply of molten metal was started, and continuous casting was performed at a casting speed of 1.5 m / min. The results of an examination of the quality of the obtained slab are shown in index form in FIG. The comparative example in FIG. 5 shows the results when continuous casting was performed under the same conditions except that the angle of the discharge port was 15 ° upward. As is clear from FIG. 5, it was confirmed that, according to the present invention, even if continuous casting is performed at a relatively high speed, the quality defects peculiar to stainless steel are very rarely caused.

In this embodiment, the case where the slab thickness is 200 mm is taken as an example, but the slab thickness is not limited to 200 mm, and when the slab thickness is thicker (for example, 260 mm) or thinner (for example, 260 mm). For example, 180mm) is also effective.

[0012]

According to the present invention, even if the casting speed is increased in continuous casting of stainless steel, the quality is not deteriorated and the production efficiency can be remarkably improved.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an angle of a discharge port of an immersion nozzle.

FIG. 2 is an explanatory diagram of the immersion depth of an immersion nozzle.

FIG. 3 is a diagram showing a situation of occurrence of quality defects in a cast slab.

FIG. 4 is a diagram showing a situation of occurrence of quality defects in a cast slab.

FIG. 5 is a diagram showing a comparison of occurrence of quality defects in cast slabs.

Claims (1)

[Claims] 1. When manufacturing a stainless steel cast slab by using a vertical bending type continuous casting machine, 5 ° above and 35 ° below the direction perpendicular to the axis of the nozzle. The immersion nozzle, which has a discharge hole with an angle within the range, is immersed to a depth of 150 to 300 mm from the mold meniscus surface of the continuous casting mold, and in this state the molten stainless steel is poured into the mold. And a stainless steel casting slab is drawn from the mold at a casting speed of 0.8 to 1.8 m / min.