JPH0714832B2 - Method for manufacturing refractory for continuous casting - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a refractory material for continuous casting, such as a slide gate or a nozzle, which is interposed between a continuous casting mold and a tundish.

[Prior Art] Usually, MgO (magnesia) is used as a refractory for continuous casting.
Since MgO-based refractory materials containing Mg have a large contact angle with molten steel, they can be expected to have higher corrosion resistance than other materials and are widely used.

However, since the MgO refractory has a large coefficient of thermal expansion,
It has the drawback of being poor in thermal shock resistance.

Conventionally, in order to deal with the above-mentioned drawbacks, (1) in addition to MgO-based aggregate, a large amount of C (carbon) is contained as a refractory aggregate to lower the coefficient of thermal expansion or improve the thermal conductivity. ) Using monoclinic ZrO ₂ (zirconia) aggregate together to obtain microcracks in the matrix during refractory production.

A method for producing a refractory for continuous casting, which aims to improve the thermal shock resistance, has been considered.

[Problems to be Solved by the Invention] However, in the MgO-C-based continuous casting refractory manufactured by the conventional manufacturing method in which a large amount of C is used as a refractory aggregate, the structure becomes brittle due to carbon oxidation and decarburization. Alternatively, there is a problem of deterioration of corrosion resistance for extremely low carbon steel grades.

Further, in the MgO-ZrO ₂ series continuous casting refractory by the conventional manufacturing method in which monoclinic ZrO ₂ is used as the refractory aggregate together, when the amount of ZrO ₂ used is small, the cubic stabilized by MgO is used. The ratio of crystalline ZrO ₂ is increased, the microcracks due to the monoclinic tetragonal phase transformation are reduced and the effect is reduced, while when the amount of ZrO ₂ used is large or when it is used as a rough angle, There is a problem that many cracks are generated in the structure and the strength is significantly deteriorated.

Therefore, an object of the present invention is to provide a method for producing a refractory for continuous casting, which is excellent in corrosion resistance and thermal shock resistance and which can enhance the bond strength of the structure.

[Means for Solving the Problems] In order to solve the above problems, the present invention provides 5 to 50 parts by weight of ZrO ₂ with respect to 100 parts by weight of MgO alone or a refractory material containing MgO to obtain a particle size of 44 to 10000 μm. 20 to 100% by weight of the prepared MgO-ZrO ₂ -based aggregate (hereinafter referred to as MZ-based aggregate), the balance being mainly M
This is a method in which a refractory raw material made of gO-based aggregate is kneaded, molded, and fired.

Here, the refractory material containing MgO, in addition to MgO, oxide,
Carbide, boride, or nitride Refractory material or one to which one or more metals are added, such as Al ₂ O ₃ (alumina), Cr ₂ O ₃ (chromium oxide), ZrB ₂ (zirconium boride), or Si ₃ N ₄ (silicon nitride) whiskers, SiC (silicon carbide) whiskers, etc. are used. The refractory material other than MgO enhances the corrosion resistance and strength of the MZ-based aggregate itself, and the proportion of the addition amount thereof is preferably 80% by weight or less based on the entire MZ-based aggregate. If it exceeds 80% by weight, the amount of MgO blended will decrease, and high corrosion resistance may not be expected, and the balance between MgO and ZrO ₂ may be unfavorable.

In addition, MgO-based aggregate means MgO, MgO.Al ₂ O ₃ (spinel) or
One or more of MgO / Cr ₂ O ₃ (chromium spinel), or the one in which Al203 is added in addition to these, in addition to these main MgO-based aggregates, as a further aggregate, it is more resistant to spatter. It is also effective to use C (carbon) together for improving the poling property or the corrosion resistance.

[Work] MZ aggregate is not only clinker melt-produced from baddeleyite and periclase or spinel, but also crushed and prepared by sintering at 1500 ° C or higher. It is good, but an electrofused product is particularly desirable in terms of controlling the size of the ZrO ₂ crystal, current manufacturing technology, and cost.

Since ZrO ₂ hardly forms a solid solution with MgO, Al ₂ O ₃ , and Cr ₂ O ₃ , MZ-based aggregates are MgO or MgO.Al ₂ O ₃ , MgO.Cr ₂ O ₃
It has a structure in which ZrO ₂ particles are dispersed in a matrix of free Al ₂ O ₃ or Cr ₂ O ₃ .

This ZrO ₂ exists as a monoclinic type, a tetragonal type or a cubic type depending on the solid solution amount of MgO. When the MZ-based aggregate is used as a refractory, microcracks are generated as follows due to the thermal history during firing or actual use.

When ZrO ₂ particles of the MZ system aggregate in was monoclinic type, ZrO ₂ by expansion and contraction in the phase transformation of monoclinic tetragonal
Microcracks are generated around the particles.

In addition, when the ZrO ₂ particles are tetragonal, a part thereof undergoes phase transformation into monoclinic type due to increase / decrease in thermal stress, and similar microcracks are generated.

Furthermore, if the ZrO ₂ particles were of cubic type, 1300-14
Microcracks are generated by annealing at 00 ° C. for destabilization, partly changing into a tetragonal phase and monoclinic phase.

Therefore, regardless of the difference in the ZrO ₂ phase in the MZ-based aggregate, microcracks are obtained in the thermal history during firing or when the product is used, and these microcracks absorb and relax the thermal stress applied to the product from the outside. Thus, the thermal shock resistance of the aggregate itself and the refractory can be enhanced. Moreover, since these microcracks are generated only in the ZrO ₂ particles and their surroundings in the MZ-based aggregate, they do not deteriorate the bond strength of the tissue.

Since ZrO ₂ is stabilized to cubic ZrO ₂ by MgO, the amount of ZrO ₂ added during preparation of the MZ-based aggregate is MgO alone or MgO.
If the amount is less than 5 parts by weight relative to 100 parts by weight of the refractory material containing, the amount of microcracks is reduced and there is no effect. If it exceeds 50 parts by weight, cubic ZrO ₂ increases and the linear thermal expansion coefficient becomes large. The thermal shock resistance is not improved.

If the particle size of the MZ-based aggregate is less than 44 μm, micro-cracks also occur in the refractory matrix, resulting in deterioration of the bond strength of the tissue.
If it exceeds 0 μm, it becomes difficult to manufacture a refractory.

If the content of MZ-based aggregate in the refractory raw material is less than 20% by weight, the total amount of microcracks in the MZ-based aggregate particles is small, and the low thermal shock resistance, which is a defect of ordinary MgO-based refractory, cannot be improved. .

[Examples] Examples of the present invention will be described below.

ZrO ₂ is added to 100 parts by weight of MgO by the required amount as shown in Table 1, and a refractory material containing MgO (MgO-Al ₂ O ₃ )
ZrO ₂ was added to each of the required amounts as shown in Table 2, and
Twelve types of MZ-based aggregates made of powder having a particle size of 44 to 5000 μm were prepared by a sintering method or a melting method.

Prepare the prepared MZ-based aggregate and MgO powder with a particle size of 0.5-5000 μm.
Blended in the proportions shown in Tables 1 and 2, further kneaded with the required amount of binder (Examples 3 and 12 further contain 3% by weight of carbon in an external ratio) and molded at a pressure of 1.5 kg / cm ^2. After doing
A refractory for a slide gate was obtained by firing at a temperature of 1600 ° C. in an oxidizing or reducing atmosphere.

Bending strength of the refractory for each slide gate, corrosion resistance index,
The thermal shock test results and practical life are shown in Tables 1 and 2 which also show the conventional refractory for slide gates and others using monoclinic ZrO ₂ as refractory aggregate.

In Table 1, the ZrO ₂ content of Example 1 corresponds to that of Comparative Example 1, and the ZrO ₂ content of Examples 2 and 3 corresponds to that of Comparative Example 2.

Bending strength and other properties were measured after pitch impregnation and volatile matter removal after firing.

Therefore, as in Examples 1 to 12, when preparing the MZ-based aggregate, Mg
The amount of ZrO ₂ added is 5 to 50 parts by weight based on 100 parts by weight of the refractory material containing only O or MgO, and the amount of MZ-based aggregate in the entire refractory raw material (excluding the binder) is 20 to 100% by weight. By doing so, the bending strength and the corrosion resistance index can be made substantially the same as those of the conventional slide gate refractory,
Moreover, it can be seen that the thermal shock resistance and the practical life can be dramatically improved as compared with the conventional method.

This is due to the fact that the micro cracks in the MZ-based aggregate particles are not affected by the difference in the crystal type of ZrO ₂ in the MZ-based aggregate due to the difference in the preparation temperature, and during the thermal history during firing or actual use of the refractory. Is obtained, and cracks do not occur in the matrix of the refractory material that binds the aggregate.

Further, in Examples 3 and 12, although carbon is added alone, and the carbon-containing refractory is reduced and fired with a large amount of binder, as can be seen from the table, bending strength, thermal shock resistance and corrosion resistance are I see that it is excellent.

[Effects of the Invention] As described above, according to the present invention, the composition of the heat history of the refractory during firing or in actual use is not affected by the difference in the crystal type of ZrO ₂ in the MZ-based aggregate. Since microcracks can be obtained only in the MZ-based aggregate particles among the refractory raw materials, the refractory material for continuous casting, which has better corrosion resistance and thermal shock resistance than the conventional method, and has a high bond strength of the structure. Can be obtained.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Takafumi Nishibe, Takashi Nishi, 1st Nanto, Ogakie-cho, Kariya city, Aichi Toshiba Ceramics Co., Ltd. Kariya factory Lamix Co., Ltd. Kariya Factory

Claims (1)

[Claims] 1. Particle size of 44 to 10000 μm by adding 5 to 50 parts by weight of ZrO ₂ to 100 parts by weight of refractory material containing MgO alone or containing MgO.
The MgO-ZrO ₂ -based aggregate prepared in 20 to 100% by weight, the balance is kneaded with a refractory raw material mainly composed of MgO-based aggregate, and molded,
A method for producing a refractory for continuous casting, which comprises firing.