JPH06226431A - Nozzle for casting - Google Patents

Abstract

PURPOSE:To provide a nozzle for molten metal casting made of a ZrO2 sintered compact partially stabilized with MgO enabling long-term stable casting as the nozzle has excellent thermal impact resistance, lessens the reaction of the molten metal components and the stabilizing MgO in the sintered compact and lessens the deterioration in its strength during use. CONSTITUTION:This nozzle for casting consists of the ZrO2 sintered compact partially stabilized with the MgO formed by compounding 0.1 to 2 pts.wt. Al2O3 and 0.1 to 1 pt.wt. SiO2 with 100 pts.wt. ZrO2 component partially stabilized with the MgO compounded with 6 to 10mol% MgO and 0.1 to 3mol% SrO as stabilizers. As a result, the specific fine structure in which monoclinic crystal phase regions are three-dimensionally continuous is formed by adding the MgO and the SrO, Al2O3 and SiO2 as the stabilizers to the ZrO2. The ZrO2 sintered compact partially stabilized with the MgO which is greatly improved in various characteristics, such as thermal impact resistance, strength at room temp. and hot and chemical stability to the high-temp. molten metal, is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a casting nozzle, and more particularly to magnesia (MgO) partially stabilized zirconia (ZrO) capable of performing stable casting for a long time.
₂ ) Sintered body casting nozzle.

[0002]

_2. Description of the Related Art ZrO ₂ contains Zr due to a volume change of about 4% accompanying the phase transformation of monoclinic ⇔ tetragonal at around 1000 ° C.
It is difficult to obtain a sintered body of O ₂ alone.

For this reason, conventionally, a method has been generally adopted in which MgO, CaO, Y ₂ O ₃ or the like is added as a ZrO ₂ stabilizer, and a sintered body stable at room temperature is obtained by firing and cooling.

Among the ZrO ₂ sinters containing these stabilizers, the MgO-stabilized ZrO ₂ sinters are excellent in thermal shock resistance, strength and fracture toughness and are used at high temperatures. It is widely used as a heat resistant structural member such as a die for extruding non-ferrous metals.

In such a MgO partially stabilized ZrO ₂ sintered body, MgO and CaO are used in combination as a stabilizer of ZrO ₂ or Al ₂ O ₃ for the purpose of improving thermal shock resistance at the expense of strength. A material in which a small amount of SiO ₂ or SiO ₂ is added has been proposed. However, it cannot be said that its thermal shock resistance is sufficient, and MgO partially stabilized ZrO ₂
Regarding the reaction between the sintered casting nozzle and the molten metal,
The reality is that little attention has been paid.

[0006]

Therefore, the conventional Mg
O partially stabilized ZrO ₂ sintered body is applied to members used under conditions involving rapid thermal shock and reaction with molten metal, such as a casting nozzle that comes into contact with molten metal at a temperature of 1300 ° C or higher. In such a case, the member is damaged by cracks caused by thermal shock, or the strength of the ZrO ₂ sintered body is deteriorated due to the reaction between the molten metal component and the stabilizer MgO in the sintered body, and further, the member. There was a problem in terms of durability such as breakage.

The present invention solves the above-mentioned conventional problems, is excellent in thermal shock resistance, and has little reaction between the molten metal component and the stabilizer MgO in the sintered body, so that strength deterioration during use is small. Therefore, an object of the present invention is to provide a molten metal casting nozzle made of a MgO partially stabilized ZrO ₂ sintered body, which enables stable casting for a long time.

[0008]

The casting nozzle of claim 1 has a chemical composition of MgO of 6 to 10 mol%,
0.1 to 3 mol% of SrO is contained, and the balance is substantially Zr.
Sintered MgO partially stabilized ZrO ₂ containing 0.1 to ₂ parts by weight of Al ₂ O ₃ and 0.1 to 1 part by weight of SiO ₂ with respect to 100 parts by weight of MgO partially stabilized ZrO ₂ component made of O _2. Characterized by consisting of a body.

A casting nozzle according to a second aspect is the casting nozzle according to the first aspect, characterized in that the MgO partially stabilized ZrO ₂ component further contains less than 2 mol% of BaO.

The casting nozzle according to claim 3 is the casting nozzle according to claim 1 or 2, wherein the MgO partially stabilized ZrO _{2 is used.}
The microstructure of the sintered body is composed of first crystal grains of cubic crystal, tetragonal crystal and monoclinic crystal having a diameter of 5 to 100 μm, and second crystal grains of monoclinic crystal. The monoclinic crystal in the crystal grain exists mainly in a region facing the grain boundary, and the monoclinic phase is three-dimensionally continuous with the second crystal grain existing in the grain boundary of the first crystal grain. It is characterized by forming a region.

The present invention will be described in detail below.

The reason why the casting nozzle of the present invention is excellent in thermal shock resistance, particularly in thermal shock during rapid heating, is that the MgO partially stabilized ZrO ₂ sintered body constituting the casting nozzle of the present invention is It is considered that the monoclinic phase region is formed three-dimensionally continuously. That is, Mg
When the O partially stabilized ZrO ₂ sintered body is rapidly heated, the monoclinic crystal in the sintered body undergoes a phase transformation into a tetragonal system. And the volume contraction accompanying it causes the stress relaxation region of the thermal stress generated by the rapid heating, but the effect is three-dimensionally continuous rather than the presence of the monoclinic phase regions dispersed. This is probably because it is more important to

Consider the reaction near the interface between the molten metal to be cast and the casting nozzle. Conventional MgO partially stabilized Z
In the case of the rO ₂ sintered body, the molten metal component that has penetrated into the grain boundaries in the sintered body reacts with the stabilizer MgO that is in solid solution in the grains, and MgO diffuses into the molten metal. ,as a result,
It is considered that near the interface of the molten metal, the amount of MgO in the sintered body decreases and the strength deteriorates in that region, so that melting loss progresses. In the MgO partially stabilized ZrO ₂ sintered body of the present invention, MgO can be added by adding SrO and BaO.
A monoclinic region that does not contain the stabilizer MgO is formed in the grain boundary region of the grains that contain. That is, the crystal grains containing the stabilizer MgO are protected by the phase not containing the stabilizer MgO, so that the molten metal component that has penetrated into the grain boundaries and MgO do not easily react with each other. As a result, the strength of the sintered body is not deteriorated near the interface with the molten metal, and it is considered that the corrosion resistance is excellent.

Incidentally, M constituting the casting nozzle of the present invention
In the gO partially stabilized ZrO ₂ sintered body, the monoclinic phase is said to be continuous. However, even if there is a partially discontinuous region, the grain boundary is not affected by additives other than the monoclinic crystal. The presence of the reaction product does not impair the effects of the present invention.

Hereinafter, M constituting the casting nozzle of the present invention
The relationship between the addition effect of each component and the microstructure in the gO partially stabilized ZrO ₂ sintered body will be described.

In the following, "mol%" means MgO.
And SrO and ZrO ₂ indicate the mole percentage of the inner portion relative to the total, and “wt%” indicates the weight percentage of the outer portion relative to the total.

In the present invention, MgO, SrO, Al
Due to the synergistic effect of the combined use of ₂ O ₃ and SiO ₂ , the above-mentioned microstructure is formed to obtain excellent thermal shock resistance and stability, and the addition of BaO increases the grain boundary products, resulting in more molten metal. It improves the stability of the ingredients.

In the present invention, the addition amount of MgO is 6 to 1
It is 0 mol%, preferably 7 to 9 mol%. MgO is 6
If it is less than mol%, not only the fine structure cannot be obtained,
The strength of the sintered body decreases. When the content of MgO is more than 10 mol%, the amount of monoclinic crystals precipitated during cooling after firing is decreased and the thermal shock resistance is deteriorated even if the fine structure is obtained. Therefore, the MgO content must be 6-10 mol%.

The amount of SrO added is 0.1 to 3 mol%, preferably 0.3 to 2 mol%. SrO is 0.1 mol%
If the amount is less than the above, the fine structure cannot be obtained, and if it is more than 3 mol%, the fine structure collapses and the thermal shock resistance also deteriorates.

When BaO is added, its amount is less than 2 mol%, preferably less than 1 mol%. BaO is 2
When it is more than mol%, the fine structure collapses and the thermal shock resistance also deteriorates.

The addition amount of Al ₂ O ₃ and SiO ₂ is Mg
M containing O and SrO and the balance being essentially ZrO ₂
gO partially stabilized ZrO ₂ component 100 parts by weight, Al
₂ O ₃ 0.1 to 2 parts by weight and SiO ₂ 0.1-1 parts by weight, preferably Al ₂ O ₃ 0.1-1 parts by weight of S
iO ₂ is 0.1 to 0.5 parts by weight. If the added amount of Al ₂ O ₃ and SiO ₂ is less than the above range, the fine structure cannot be obtained and the thermal shock resistance is inferior, and if it is more than the above range,
The fine structure cannot be obtained, and the strength is reduced.

In the casting nozzle of the present invention made of such a MgO partially stabilized ZrO ₂ sintered body, the mixed powder obtained by mixing the respective components so as to have the predetermined chemical composition is formed into a predetermined shape. It can be manufactured by molding and calcining the obtained molded body at a calcining temperature of 1500 to 1800 ° C. in the atmosphere. If the firing temperature is lower than 1500 ° C., the fine structure cannot be obtained, and if the firing temperature is higher than 1800 ° C., it is difficult to realize the firing furnace in terms of technology, cost and mass production.

The MgO and other component raw materials used in the production of the MgO partially stabilized ZrO ₂ sintered body of the casting nozzle of the present invention should be in the form of oxides during the production process of the sintered body. In addition to the respective oxides, hydroxides, carbonates and the like can be used. It is also possible to use a raw material synthesized from a liquid phase in which each component is in a more uniform mixed state.

[0024]

EXAMPLES The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples unless it exceeds the gist.

Examples 1 to 8a and 8b, Comparative Examples 9 to 14 Mg was used as a high-purity ZrO ₂ raw material having an average particle size of 1 μm or less.
O, SrCO ₃ , BaCO ₃ , Ca (OH) ₂ , Al ₂
Each powder of O ₃ and SiO ₂ was added so that the chemical composition after firing would be the ratio shown in Table 1 and wet-mixed. The obtained mixed powder was calcined at 1200 ° C. for 4 hours, then wet-crushed, and a molding organic binder was added to obtain a mixed powder having a uniform chemical composition. This powder was subjected to CIP at a pressure of 1000 kg / cm ² and then fired at 1750 ° C. for 5 hours to obtain a sintered body sample.

Each sample was evaluated and the results are shown in Table 1.

The evaluation method is as follows:
The method based on the S-bending test and the thermal shock resistance were measured by a rapid heating test method in which a tube of one-end closed tube type was immersed in molten steel at 1700 ° C. Regarding the fine structure, a method of observing the sintered body sample by mirror etching and then performing chemical etching and SEM observation was adopted. FIG. 1 shows an SEM photograph of the sintered body having the fine structure of claim 3 (sintered body of Example 6) after chemical etching. In the figure, it is a monoclinic region in which a band-shaped black portion is continuously formed.

As is clear from Table 1, MgO-SrO
-Al ₂ O ₃ -SiO ₂ mixed system and MgO-SrO-B
The MgO partially stabilized ZrO ₂ sintered body having the aO—Al ₂ O ₃ —SiO ₂ mixed system and having the above microstructure has excellent thermal shock resistance and high strength, and is extremely effectively used as a casting nozzle. be able to.

[0029]

[Table 1]

Further, regarding Example 6 and Comparative Examples 10 and 13, a MgO partially stabilized ZrO ₂ sintered body plate having a thickness of 10 mm × 10 mm × 3 mm was prepared. Place a 2mm x 2mm x 2mm cobalt-based alloy on this plate,
A corrosion resistance test was performed under static conditions by raising the temperature to 1500 ° C. in an Ar atmosphere. The corrosion resistance was evaluated by measuring the contact angle as a measure of the wettability between the alloy and the plate and performing the structure / composition analysis of the cut surface of the reaction part of the alloy and the plate with SEM / EPMA. The results are shown in Table 2.

The following is clear from Table 2. That is,
Regarding the contact angle, all samples were 90 ° or more, and there was almost no difference.

Regarding the change in structure, in the sample of Example 6,
Although the alloy component penetrates into the grain boundaries of the sintered body, the grain boundary region is a monoclinic crystal that does not contain a stabilizer, so it is difficult to contact the stabilizer present in the grains, and therefore the structure and composition Almost no change was observed, and it was confirmed that the material had high corrosion resistance.

On the other hand, in the samples of Comparative Examples 10 and 13, the alloy component penetrates into the grain boundaries of the sintered body and reacts with the stabilizer existing in the grains, and the stabilizer is alloyed through the grain boundaries. It has moved to the contact surface with. As a result, destabilization of the ZrO ₂ particles containing the stabilizer proceeds inside the sintered body,
It was found that the rO ₂ grains were subdivided and the strength of the sintered body was reduced, resulting in damage from the interface with the alloy.

[0034]

[Table 2]

Further, regarding Example 6 and Comparative Examples 10 and 13, MgO having an outer diameter of 30 mm, an inner diameter of 4 mm and a length of 30 mm.
Partially stabilized ZrO ₂ quality nozzles were manufactured, each nozzle was set in an actual machine, and an evaluation test was conducted under the following operating conditions.

Operating Conditions The molten alloy type is a cobalt alloy. The holding temperature during casting is 1500 ° C. As a result, with the material of Example 6,
There was no cracking due to thermal shock, and stable casting was possible for 8 hours or more.

On the other hand, in the materials of Comparative Examples 10 and 13, low durability within 2 hours due to deterioration of nozzle surface properties due to melting loss due to cracking due to thermal shock and destabilization due to segregation of the stabilizer. I only got it.

As a result, the MgO partially stabilized Z of the present invention is obtained.
It can be seen that the durability is dramatically improved by using the casting nozzle made of the rO ₂ sintered body as compared with the conventional material.

[0039]

As described above in detail, according to the casting nozzle of the present invention, the thermal shock resistance, the strength at room temperature and hot, the chemical stability against molten metal at high temperature, etc. Provided is a casting nozzle which can be stably used in casting.

According to the casting nozzles of claims 2 and 3, a casting nozzle further excellent in the above characteristics is provided.

[Brief description of drawings]

FIG. 1 is a SEM photograph (500 times) showing a fine crystal structure of a MgO partially stabilized ZrO ₂ sintered body.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hideki Haishi 6-31-24 Sakuragaoka Nishi, Sanyo-cho, Akaban-gun, Okayama Prefecture (72) Inventor Nobuo Ayuzawa 5-6-25 Kachi, Okayama-shi, Okayama (72) Invention Akira Shirahita 18-39 north of Kamido, Okayama City, Okayama Prefecture (72) Inventor Masaaki Takeuchi 390 Higashikataue, Bizen City, Okayama Prefecture (72) Teruhiko Takeda Higashikatagami, Bizen City, Okayama Prefecture 660

Claims (3)

[Claims] 1. A chemical MgO 6-10 mole percent composition of SrO containing 0.1 to 3 mol%, MgO partial balance of substantially ZrO ₂ stabilized ZrO ₂ component 100
0.1 to ₂ parts by weight of Al ₂ O ₃ and SiO ₂ with respect to parts by weight
MgO partially stabilized ZrO containing 0.1 to 1 part by weight of ₂
A casting nozzle characterized by comprising ₂ sintered bodies. 2. The casting nozzle according to claim 1, wherein Mg
A casting nozzle characterized in that the O partially stabilized ZrO ₂ component further contains less than 2 mol% of BaO. 3. The casting nozzle according to claim 1 or 2, wherein the fine structure of the MgO partially stabilized ZrO ₂ sintered body is a cubic structure having a diameter of 5 to 100 μm, a tetragonal system and a monoclinic system. The crystal grains and the second crystal grains composed of monoclinic crystals are present. The monoclinic crystals in the first crystal grains are mainly present in the region facing the grain boundaries, and A casting nozzle characterized in that a monoclinic phase region which is three-dimensionally continuous is formed together with the second crystal grains existing at grain boundaries.