JPS59162174A - Continuous casting nozzle - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention can be used in the operation of continuous steel casting, and is extremely effective especially in areas that are in contact with the boundary between ladle slag or mold powder and molten steel (hereinafter referred to as P and L parts). This invention relates to a continuous casting nozzle that has excellent corrosion resistance and excellent spalling resistance.

The nozzle for continuous casting of steel is connected to completely feed the molten steel from the ladle to the tundish and to the tundish caramold, and at the same time prevents oxidation of the molten steel, prevents turbulence of the molten steel during pouring, and entrains slag. It is a member that plays an important role in improving the quality of slabs by reducing non-metallic inclusions in slabs.

Conventionally, the materials used for continuous steel casting nozzles include bath-fused silica, alumina-graphite, and zirconia-graphite, but each has its advantages and disadvantages. Because siliceous substances crystallize at high temperatures,
Spall resistance is insufficient for regular operation, and high manganese steel has the drawback of being severely eroded, and alumina-graphite has excellent corrosion resistance and spall resistance against molten steel. However, a typical example is that the P and L portions have a drawback that they are extremely susceptible to melting damage.

As a solution to these shortcomings, for example,
Zirconia-graphite immersion nozzles are disclosed in No. 5579 and Japanese Unexamined Patent Publication No. 56-37275. However, in recent years, due to the diversification of the temperature of molten steel, increase in passing sensitivity, etc. in order to stabilize operations in continuous steel casting, the properties required of these parts have become increasingly severe, and the above-mentioned prior art The reality is that even zirconia-graphite materials have insufficient durability, and improvements are needed.

In view of the current situation, the present invention has been developed by limiting the properties of zirconia aggregate, thereby making it highly resistant not only to molten steel but also to ladle slag or mold powder, which is a particular concern. This was done with the aim of proposing a continuous casting nozzle that has extremely excellent corrosion resistance even in the P and L parts.
The object of the present invention is to provide a continuous casting nozzle that can be obtained using a ZrO2 solid solution as a main material in which aO is stably distributed in a crowd in a crystalline phase.

The present invention will be explained below based on an example of implementation.

As a zirconia aggregate as a raw material for refractories, free C
Without aO or calcium zirconate, Ca
O is distributed in the crystal phase in a stable state, and a suitable one of cao-i in this stable state is selected from 7' (ZrO2 solid solution), and by using this aggregate, the nozzle Excellent corrosion resistance against melting loss at the P and L parts can be imparted.

By the way, when a conventional nozzle is used in continuous casting of steel, the P and L portions are abnormally damaged by melting, and as a result, the life of the nozzle is often limited. Although the mechanism of this erosion has not been clearly analyzed, active oxygen ions generated at the interface between molten steel and slag oxidize the carbon component of zirconia-graphite, and as a result, localized ladle slag and mold It is thought that a low melting point compound that is easily wetted by the inner powder is produced, and the repetition of this oxidation and production of the low melting point compound leads to abnormal melting loss of the j5 P and L parts.

In view of these findings, the present invention uses CaO-stabilized Zr
The O2 solid solution has oxygen ion conductivity, and in order to make this phenomenon more effective, we will consider a CaO distribution lid to maintain high oxygen ion conductivity. This improves the corrosion resistance of the area that comes into contact with the interface with note powder, etc.

That is, a Z r O2 solid solution in which CaO is crowdedly distributed produces a substitutional solid solution having a cubic fluorite structure in which CaR+ is substituted at the position of Zr'+. In this case, the lattice positions of Zr'+ in the ZrO2 crystal are partially replaced by cations with a low valence of Ca2, so if there is a lack of positive charge, the entire crystal becomes electrically neutral. In order to maintain this, a vacancy with a deficient charge is created at the position of anions (oxygen ions), resulting in oxygen ion conductivity.

Regarding zirconia aggregate, the amount of CaO in the aggregate is 13m
It is reported that the electrical conductivity reaches its maximum when the temperature is around 1% (Ceramics, ■(8) (1976) Bokutachi, Ikeda, P19
8-210) Oxygen ion conductivity is also a natural tendency, and as shown in FIG.
This agrees with the inventor's experimental results, which were good in the range of 20.11101%.

On the other hand, in this case, if a clinker containing a calcium zirconate compound such as CaZrO3 or free CaO is used, even if the amount of CaO is 10 to 20 mol %, the oxygen ion conductivity of the clinker will also decrease.
Considering the erosion mechanism, it is undesirable because it associates with the pot slag and the powder in the mold, creating a lower melting point compound.

In the present invention, by utilizing this oxygen ion vacancy, some of the active oxygen ions generated at the interface of the molten steel are
This is based on moving the vacancies in the O2 crystal, reducing the oxidation of carbon in the zirconia-graphite, and ultimately improving the corrosion resistance in the P and L parts of the refractory. Therefore, the present invention can convert CaO to lθ without intervening free CaO or calcium zirconate compounds.
Z r 02 solid solution containing ~20 mol % distribution is used as zirconia aggregate, and this zirconia aggregate has a weight value of 60~90 and black @10~4.
0% by weight and as necessary -(Si, AI, B4C,
5in2, SiC, etc. (7) IFJ or 'fd2 or more 0
This is a continuous casting nozzle made by adding and kneading 10% by weight of a normal binder, molding and drying, and then firing in a reducing atmosphere.

In this composition range, if the zirconia aggregate is less than 60% by weight, there is no effect of improving corrosion resistance, and if it is more than 90% by weight, the amount of graphite becomes too small, causing problems in wettability and spall resistance. Occurrence 2: Exceeding this range is not desirable.

Next, various specific examples of the present invention using the fireproof material formulated in this way will be shown. An immersion nozzle for continuous casting of steel was manufactured with the composition shown in Table 1, and at the same time a comparative nozzle made of a material outside the scope of the present invention was also manufactured, and both were installed between the tundish and the mold, and the immersion nozzle was installed in a molten steel ladle. I did a real hot water test. The results are shown in Table 1. The continuous casting nozzle of the present invention has a melting rate of about 40 mm, especially in the area where it touches the interface between the pot slag or the powder in the mold and the dissection, compared to the comparative example. It can be seen that it has excellent corrosion resistance.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between Ca0iB4 (contained in Zr○2 solid solution, which is zirconia aggregate), and the erosion index. Name: Person responsible for continuous casting nozzle supplement 11) 1'1/Relationship with 1 system Patent application agency
1 person and 1 other person 1-1 Lee J. Showa 1999 Monthly oral assistance,
Positive subject matter Description, claims column, ■ The scope of claims will be amended as follows. "Contains 10 to 20 mo1% of CaO, free (D C
Z that does not generate aO or calcium zirconate compounds
Continuous casting nozzle made by firing rO2 solid solution as aggregate with 50-9Qwt96 and graphite. ” ■ Ming #l, page 6, line 9 to line 13, “
This zirconia aggregate was added and kneaded, and the phrase ``This zirconia aggregate was mixed with ~90wt%, graphite 10~4Qwt%, and St, AI, B4C%.
5i02. One or more types of SiC etc. are added to θ~10wt and a regular binder is added and kneaded. ■ Specification, page 6, line 15, “zirconia aggregate is 6
0] Correct the statement ``i amount q'' to ``zirconia aggregate is 50 wt q.'' ■ In the specification, page 6, line 17, "90% by weight" should be corrected to "9Qwt". 450

Claims (1)

[Claims] Contains 10-20 mol% of CaO, free CaO
ZrO does not produce calcium zirconate compounds or calcium zirconate compounds.
A continuous casting nozzle made by kneading and molding 60 to 9 Q wt % of 2 solid solution as aggregate and 10 to 40 Q wt % of graphite with a normal binder, and then firing in a reducing atmosphere.