JPS6015588B2 - Immersion nozzle for continuous casting - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a continuous casting nozzle which is connected from a tundish to a mold and is used for the purpose of preventing molten steel from oxidizing, controlling the flow of molten steel in the mold by splashing, and preventing slag from being entrained. It is about improvement.

Conventionally, fused silica or alumina-graphite groove nozzles have been used from the viewpoints of spall resistance, corrosion resistance, and airtightness.

However, although the fused silica erosion nozzle has excellent corrosion resistance and spalling resistance against mold powder, it has the disadvantage that it suffers from large melting loss when compared to high manganese steel. On the other hand, an alumina-graphite groove nozzle is a groove nozzle that uses alumina, which has excellent corrosion resistance, as an aggregate, and combines this with graphite, which has a high thermal conductivity, to improve corrosion resistance and spall resistance.

It is desirable for this type of encroachment/sludge to have a large amount of graphite in order to improve spall resistance, but in this case, the corrosion resistance will be poor, so the amount of graphite blended is naturally limited. Therefore, in order to obtain more stable spalling resistance, an erosion nozzle has been proposed in which fused quartz is added to suppress thermal expansion of the erosion nozzle body. However, the addition of fused silica results in a decrease in the corrosion resistance of high-manganese steel, resulting in greater damage to the inner tube of the erosion nozzle, which not only makes it impossible to use it as a twill erosion nozzle for a long time, but also has a negative effect on the quality of the steel. was. The present inventors conducted a detailed study on the usage conditions of the erosion nozzle and the damage mechanism of the inner tube, with the aim of solving the problems of spall resistance and corrosion resistance.

As a result, infiltration nozzles are generally heated at a temperature of 900 to 1200°C for the purpose of preventing cracking at the initial stage of coinage and suppressing metal adhesion, so the important point for spall resistance is the preheating temperature It was found that it is safe against temperature changes up to a casting temperature of around 1550°C.

In addition, the corrosion resistance of the alumina-graphite-silica system is reduced because the silica is reduced by the aluminum and manganese of the steel and dissolves into the steel, or is decomposed by the carbon contained in the penetrating nozzle, and evaporates and disappears. It was found that this was caused by The present invention strives to improve the erosion nozzle based on the above results, and provides an erosion/spall nozzle with extremely excellent corrosion resistance and spalling resistance.

The gist is that zirconia is 6-55% by weight.
, silica-zirconia clinker containing 45-94% silica and uniformly dispersing zirconia crystals in fused silica, 3-35% alumina, 25-65% alumina, and 5% graphite.
This is an abrasive nozzle for continuous casting characterized in that it consists of ~45%.

That is, the present invention provides an erosion nozzle in which corrosion resistance and spalling resistance can be significantly improved by combining a silica-zircon type clinker with a graphite-alumina material. The silica-zirconia clinker shown here is made by uniformly dispersing fine zirconia crystals in amorphous fused silica.
Although it exhibits a slightly high thermal expansion up to 0, at higher temperatures, the monoclinic zirconia contained in the clinker undergoes volumetric contraction and has a characteristic of changing to a negative coefficient of thermal expansion. Therefore, in an erosion nozzle that requires thermal stability against temperature changes from a preheat temperature of 900 to 120,000 °C, this silica-zirconia clinker is an alumina-graphite-silica bond with fused silica. It has a much greater effect on improving spall resistance than a nozzle.
In addition, since this clinker contains zirconia in silica, zircon is formed at a temperature of about 1450 qo.
Therefore, when silica is used in rough combination with graphite-alumina, selective dissolution of aluminum and manganese in steel and decomposition of carbon in a reducing atmosphere are suppressed, and inner pipe erosion is suppressed. The present invention, in which a silica-zirconia clinker is coarsely combined with the graphite-alumina material described above, not only improves spalling resistance, but also solves the problem of decreased corrosion resistance that had been a problem with alumina-graphite-silica bonding nozzles. This made it possible to operate multiple coins and significantly improve the quality of steel.

The silica-zirconia clinker used in the present invention is a clinker in which fine zirconia crystals are uniformly dispersed in amorphous fused silica using the same manufacturing method as conventional fused silica, and the size of the zirconia grains is 1 to 1. 20 grains is preferred, but the particle size is not limited to this.

Regarding the setting range of the amount of zirconia in the silica-zirconia clinker, if it is less than 6% by weight, the corrosion resistance against molten steel will be poor, and if it exceeds 55% by weight, the shrinkage due to transformation of monoclinic zirconia will increase, resulting in poor spalling resistance. .

Therefore, a range of 6 to 55% by weight is desirable. Also, regarding the setting range of silica zirconia clinker content, see 3.
If it is less than 35% by weight, the spalling resistance will be poor, and if it exceeds 35% by weight, the corrosion resistance against molten steel will be poor. For this reason 3
A range of 35% by weight is desirable. Alumina is blended because it has an extremely high softening point and excellent corrosion resistance against molten steel, and preferably haze-fused alumina or competitive alumina with an alumina content of 95% by weight or more.

Regarding the setting range of its blending amount, if it is less than 25% by weight, the corrosion resistance will deteriorate by 1, and if it exceeds 65% by weight, the thermal expansion of the infiltration nozzle will increase and the spalling resistance will deteriorate.
A range of 5 to 65% by weight is desirable.

Since graphite has extremely high thermal conductivity and is extremely difficult to wet with molten steel, the present invention adds graphite to an extent that does not reduce corrosion resistance, thereby preventing molten steel and flux from penetrating into the corrosive nozzle pores. This prevents see-through and improves spall resistance. As the raw material for graphite, natural flaky graphite is preferred, but any graphite commonly used for refractories may be used as long as the ash content is not excessive. Regarding the setting range of its blending amount, if it is less than 5% by weight, the spalling resistance will be poor, and if it exceeds 45% by weight, the corrosion resistance will be poor, so a range of 5 to 45% by weight is desirable.

Here, it is also possible to suppress oxidation and improve corrosion resistance by substituting a part of graphite with silicon carbide.

Furthermore, it is also possible to add metal silicon, ferrosilicon, feldspar, etc. for the purpose of imparting hot strength during use and maintaining the strength of the structure due to oxidation and decarbonization caused by free oxygen, etc. in the total steel. The present invention will be explained below based on examples.

Example 1 Pitch was added as an organic binder to the raw material mixture shown in Table 1 and kneaded, rubber press molded at a pressure of 1000 k9/ground, and this molded product was reduced at a temperature of 120 p○. Fired.

Its quality characteristics are shown in Table 2. These products of the present invention were used in an erosion nozzle for continuous casting having an inner diameter of 70 mm.

As a result, conventional product 5 suffered from spalling in the early stages of coining and had to be discontinued.Also, conventional product 6 could be cast for 3 hours but had an enlarged inner diameter of 830mm, whereas both products of the present invention had an enlarged diameter and an enlarged diameter. There was almost no enlargement of the discharge hole, and it could withstand up to 9 hours of casting, confirming its effectiveness. Table 1 Table 2 *High frequency induction furnace melting test

Claims (1)

[Claims] 1 Zirconia 6-55%, silica 45-94% by weight
3-35% silica-zirconia clinker containing 3-35% of zirconia crystals uniformly dispersed in fused silica.
, 25-65% alumina and 5-45% graphite.