JPH0134709B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a continuous casting nozzle capable of producing ultra-low [C] steel, for example, [C]≦15ppm, for cold-rolled or surface-treated steel sheets for ultra-deep drawing. It is related to.

[Conventional technology]

Generally, continuous casting of slag and large cross-section blooms usually employs a casting method using a submerged nozzle and powder. One of the main purposes of this is to prevent molten steel from oxidizing between the tundish and the mold, and another purpose is to float as much as possible of inclusions brought into the mold and absorb them into the powder. Therefore, for the former purpose, when installing the immersion nozzle by the exterior method, it is necessary to maintain a non-oxidized state without drawing air from the joint, and for the latter purpose, it is necessary to maintain the non-oxidized state by not sucking air from the joint. It is important to select a nozzle shape that matches the cross-sectional shape, area, and casting speed of the slab.

The material of the immersion nozzle is related to the operation and quality of continuous casting, such as the occurrence of melt damage and nozzle clogging, so it is important to select a material that is compatible with the casting steel type and casting conditions. The material is high
Mn steel is made of alumina-graphite, which has less corrosion damage due to Mn, and low-Mn steel is made of fused silica, which is relatively resistant to nozzle clogging and is relatively resistant to thermal shock.

FIG. 5 is a longitudinal sectional view of a conventional immersion nozzle used in an air seal for continuous casting, and FIG. 6 is a longitudinal sectional view of a conventional tundish immersion nozzle.

In FIGS. 5 and 6, an air seal or stopper type immersion nozzle 1 is used for molten steel 3 charged into a tundish or mold 2 as shown by the arrow.
It is immersed inside. The material of these air seal or stopper type immersion nozzles 1 is mainly composed of alumina graphite 4, and as shown in FIG. It is being
Note that 8 is a stopper, 9 is a contact surface with the stopper, 10 is an immersion nozzle outlet, and 11 is a sleeve.

Using the immersion nozzle shown in Figures 5 and 6,
When producing ultra-low [C] steel (for example, [C]≦15ppm) for cold rolling or surface treatment steel sheets for ultra-deep drawing, [C] in alumina graphite 4 is molten steel 3.
It is picked up inside. This causes an increase in [C] in the molten steel, so it is common to use fused silica (molten steel quartz) instead of alumina graphite as the material for the immersion nozzle. In the case of this material, the conventional submerged nozzle shown in FIG. 5 had poor erosion resistance in the slag line 5 and could not be used for a long time.

[Problem that the invention seeks to solve]

The present invention provides an immersion nozzle for use in manufacturing ultra-low [C] steel for cold-rolled or surface-treated steel sheets for ultra-deep drawing by continuous casting, without reducing corrosion resistance against slag and [ C] The purpose is to create a structure that can minimize pickup.

[Means for solving problems]

Regarding the materials of the immersion nozzle, fused silica has poor slag erosion resistance, and alumina graphite has drawbacks such as [C] pick-up into molten steel.The present invention was made to solve these drawbacks. The first aspect of the present invention is that the inner side that does not come into contact with the slag in the tundish or mold is made of fused silica with a thickness of 7 to 30 mm, and the outer side that comes into contact with the slag is made of two layers of alumina graphite. The shape is wide taper 1.5mm/
The second aspect of the present invention is a continuous casting nozzle with a thickness of 7 to 30 mm on the inside that does not come into contact with the slag in the tundish or mold.
The outer surface that contacts the slag is made of three layers of zirconia carbon and alumina graphite, and the surface that contacts the molten steel stopper of the nozzle is made of alumina graphite, and the shape is a wide taper 1.5. This is a continuous casting nozzle characterized in that it is rated mm/m or more and is used for ultra-low carbon steel.

[Effect]

The continuous casting nozzle of the present invention has a two-layer structure of fused silica on the inside (non-slag contact surface) and alumina graphite on the outside (slag contact surface). This problem has been solved, and the pick-up of [C] into molten steel is suppressed, and the corrosion resistance against slag is not reduced.

Further, the thickness of the fused silica is 7 to 30 mm, preferably 10 to 30 mm in the case of a submerged nozzle for an air seal pipe, as a thickness that does not cause breakage.

In addition, to prevent the fused silica pipe from falling during casting, the taper of the upper width should be 1.5 mm/m or more, preferably 3 mm/m or more in the case of an internal tundish immersion nozzle, to prevent flaking during casting. do not.

In addition, in the case of an interpolated tundish immersion nozzle,
One part of the outer part that contacts the slag surface may be made of zirconia carbon as in the past, and the other outer part may have a three-layer structure of alumina graphite.

Next, examples of the present invention will be described below.

An example is shown.

〔Example〕

FIG. 1 is a longitudinal cross-sectional view of a submerged nozzle used in the air seal for continuous casting of the first invention, and FIG.
FIG. 7 is a longitudinal cross-sectional view showing an embodiment of the interpolated tundish immersion nozzle of the second invention.

In the immersion nozzle 1 shown in FIG. 1, in order to prevent large erosion loss of the contact portion 6 with the slag line 5 on the molten steel surface, the outer side 12 that contacts the slag is made of alumina graphite, and the inner side 13 that does not make contact is made of alumina graphite.
The material is made of fused silica. Furthermore, the nozzle shape is made wider, the fused silica sleeve 11 is tapered at 1.5 mm/m or more to prevent it from falling during casting, and the thickness of the fused silica is set to 10 to 30 mm to avoid breakage. did.

In addition, in the stopper-type immersion nozzle 1 shown in Fig. 2, conventional zirconia carbon is used to maintain the melting resistance of the contact portion 6 with the slag line 5 on the molten steel surface, and the stopper contact surface 9 at the top of the nozzle is melt-resistant. In order not to change the damage properties, alumina graphite is used, and the inner part 13 is made of fused silica. Furthermore, the nozzle shape has a wide taper at the top, with a taper of 3 mm/m or more,
The thickness of the fused silica was set to 7 to 30 mm to avoid breakage.

Using the immersion nozzle configured as described above, the nozzle of the present invention (marked with ●) of picking up [C] from RH (degassing treatment) of ultra-low carbon material ([C]≦15ppm) to refractory material between slabs. A comparison of the conventional nozzles (marked with circles) shown in FIGS. 5 and 6 is shown in FIGS. 3 and 4, respectively. As is clear from Figures 3 and 4, from the graph of the relationship between RH end [C] (ppm) and slag [C] ppm, by using the nozzle of the present invention, [C] pick-up improved by 5 ppm. and [C]
It has also become possible to suppress pickup to 0ppm.

〔Effect of the invention〕

The continuous casting nozzle of the present invention does not reduce corrosion resistance to slag and does not reduce corrosion resistance to molten steel when producing ultra-low [C] steel for ultra-deep drawing cold-rolled or surface-treated steel sheets by continuous casting. It is useful because it can minimize the [C] pick-up and prevent the [C] pick-up contamination of ultra-low [C] steel, which could not be achieved with conventional nozzles.

[Brief explanation of drawings]

FIG. 1 is a vertical sectional view of a first embodiment of the present invention applied to an air seal immersion nozzle, FIG. 2 is a longitudinal sectional view of a second embodiment of the present invention of an internal tundish immersion nozzle, and FIG. Figure 4 is a graph of the relationship between RH end [C] and slab [C] in the first and second embodiments, respectively, and Figures 5 and 6 are graphs of conventional air seal submerged nozzles and internal FIG. 3 is a longitudinal cross-sectional view of the insert-type tundish immersion nozzle. In the figure, 1: immersion nozzle, 2: tundish or mold, 3: molten steel, 5: slag line,
6: Contact portion with slag, 7: Zirconia carbon, 9: Contact surface with stopper, 11: Sleeve, 12: Outside contact with slag, 13: Inside.
In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. The inner side that does not come into contact with the slag in the tundish or mold is made of fused silica with a thickness of 7 to 30 mm, and the outer side that comes into contact with the slag is made of two layers of alumina graphite. A continuous casting nozzle characterized by having a wide taper of 1.5 mm/m or more and being used for ultra-low carbon steel. 2 The inner side that does not come into contact with the slag in the tundish or mold is made of fused silica with a thickness of 7 to 30 mm, and the outside that comes into contact with the slag is made of three layers of zirconia carbon and alumina graphite, and the molten steel stopper of the nozzle is made of fused silica. The contact surface is made of alumina graphite, and the shape is wide and tapered.
A continuous casting nozzle characterized by having a diameter of 1.5 mm/m or more and being used for ultra-low carbon steel.