JP5302562B2 - Metal melting crucible and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a crucible for melting metal and its manufacturing method for preventing erosion, and obtaining a robust modified layer to prevent separation of the modified layer simultaneously with separating work of molten steel attached to an inner surface, by forming uniform CaO-ZrO<SB>2</SB>eutectic structure not by surface coating of zirconia powder, but uniformly coating CaO with zirconia precipitating from liquid by molding and baking CaO as a raw material by using liquid zirconium chelate as a binder. <P>SOLUTION: In this crucible for melting metal mainly composed of calcium oxide (CaO) used in a vacuum melting furnace, the powder of CaO as the raw material is molded and baked while using the liquid zirconium chelate as the binder to precipitate uniform CaO-ZrO<SB>2</SB>eutectic structure on CaO as aggregate. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a crucible for melting metal used for producing a high-purity alloy having a low impurity content and a method for producing the same.

  Impurity elements C, N, O, S, etc. contained in the material cause problems that the workability, toughness, corrosion resistance, etc. of the alloy are lowered, and the material is difficult to homogenize and the yield is reduced in the manufacturing process. The problem was that the properties of the material could not be maximized. For this reason, various methods for reducing these impurities, ultra-purifying the metal, and maximizing the characteristics of the material have been studied. As one of the methods, a vacuum induction melting furnace (VIM) is used. A method for melting and refining under vacuum is known.

A schematic view of a melting crucible used for this vacuum melting is shown in FIG.
The outline of the vacuum melting method is as follows. First, the metal material 02 to be dissolved is put in the crucible 01, and then the inside of the crucible 01 is evacuated and replaced with argon (Ar) gas to reduce the oxygen amount in the crucible 01 to a low level. . Then, the metal material 02 melts and becomes a liquid (melting down) in an Ar gas atmosphere. Thereafter, after the melting temperature reaches the target temperature, aluminum (Al), which is a deoxidizer, is added to produce steel.
The characteristics of the metal material are affected by the oxygen that forms the oxide, and the vacuum melting can reduce the amount of oxygen to the limit, so that the material characteristics can be dramatically improved, but a trace amount of oxygen remains. Therefore, trace amounts of oxygen are also removed by adding Al, which is a deoxidizer having a high deoxidation effect.
Further, in order to effectively reduce S and O in a metal, a calcia (CaO) crucible having an effect of cleaning molten steel is used in vacuum melting.

However, the CaO crucible used in the vacuum melting as described above has a problem that the life of the crucible is short because it must be replaced after three to five times of use due to severe melting loss. Particularly, the side wall 03 close to the molten steel interface shown in FIG. 4 and the side surface 04 close to the crucible bottom are severely melted.
This damage to the CaO crucible is due to the formation of a low melting point compound CaO—Al ₂ O ₃ eutectic by reaction with Al used for deoxidation of molten steel. That is, since the melting point of the CaO—Al ₂ O ₃ eutectic is about 1400 ° C., the melting temperature is about 1600 ° C. at the time of melting iron in vacuum melting, resulting in loss of several millimeters.

Therefore, the present applicant has found that zirconia (ZrO ₂ ) having a high eutectic temperature with CaO is effective for extending the life of the crucible, and applied a slurry in which zirconia powder is dispersed in ethanol to the surface of the crucible. And, it has been found that by firing this at a high temperature of about 1500 ° C., CaO—ZrO ₂ having a high melting point (about 2260 ° C.) is formed, and an application has been filed for dramatically improving the life of the crucible (not yet). Open technology, hereinafter referred to as prior application technology ).

An outline of this prior application technique will be described with reference to FIG. First, materials to be applied (calcia stabilized zirconia (CSZ) powder, dispersion medium, ethanol) are prepared (S01). Next, a slurry is prepared using the material and ethanol as a solvent (S02). Next, as a pretreatment of the existing CaO crucible, the surface is smoothed with paper (S03), and ethanol and slurry are applied (S04). Then, after natural or hot air drying (S05), firing at 1600 ° C. (S06) and storage (S07) are performed to deposit a CaO—ZrO ₂ eutectic on the inner surface of the crucible. I am letting.

On the other hand, for example, Patent Document 1 is known as a measure for preventing chemical erosion of a crucible used for vacuum melting. Patent Document 1 discloses a metal melting crucible in which zirconia (ZrO ₂ ) remains on the surface of a vessel wall including the inner peripheral surface of a crucible made of an inorganic refractory.

JP 61-116284 A

  However, the zirconia that remains on the surface of the vessel wall of the crucible disclosed in Patent Document 1 is merely a zirconia compound solution applied to the fired surface. In this method, a very small amount of zirconia is only adhered to the calcined calcia surface, and it is difficult to obtain a dramatic effect. Monoclinic zirconia precipitated from the salt is stable in quantity and hardly reacts with CaO because of its small quantity and stable firing surface. Therefore, it is considered that a stabilized zirconia layer is not formed by reaction with CaO on the surface of the vessel wall of the CaO crucible polished as in the present invention. Therefore, although it is a monoclinic crystal at room temperature, it is known that a structural phase transition from monoclinic to tetragonal crystal when the temperature is increased, and a cubic phase transition when the temperature is further increased. Since it accompanies a change, it easily peels from the crucible surface and does not contribute to the modification of the CaO crucible. For this reason, the crucible disclosed in Patent Document 1 in which zirconia remains in the crucible has a problem that the residual zirconia leads to destruction, and thereafter chemical erosion cannot be prevented.

  Furthermore, in the method disclosed in Patent Document 1, the inner surface of the crucible is impregnated with an aqueous solution of a compound such as zirconium chloride under reduced pressure, and the zirconium compound remaining in the pores is converted into zirconia by heating. Is highly hydratable, and when this method is used, CaO expands with water, which is not suitable because it damages the base material of the CaO crucible.

  In addition, the CaO crucible used for vacuum melting may be broken due to the thinning due to chemical erosion as described above, but the CaO crucible itself is lower in strength than the crucibles of other materials. Insufficient mechanical strength and internal thermal stress are likely to cause cracks. For these reasons, cracks may occur due to molten steel several times, making it unusable.

In the prior application technique, since the particle diameter of the zirconia powder is several microns, the modification depth by coating is limited to about a few millimeters, and normal melting (the viscosity of the molten steel is sufficiently lowered and discharged from the crucible) If there is a lot of chromium in the melted material, it will not cause problems, but if the molten steel is melted at a high viscosity, the remaining material will adhere to the crucible if it is not discharged properly, and it will not be mixed into the material to be melted next. Therefore, when removing from the crucible surface, the modified layer may be peeled off simultaneously with the remaining material.

As shown in FIG. 6, when the modified layer B on the inner surface A of the crucible is peeled off, the modification effect is lost, and the melt damage D proceeds from the peeling point C. There is a problem that the crucible must be replaced.
As a result, although it is a modified crucible that can be used 10 times or more, it must be broken and replaced, which increases the cost of melting and reduces costs related to manufacturing equipment, raw materials, etc. by extending the crucible life. The effect cannot be obtained.

Therefore, in view of the problems of the conventional technique, the present invention is not applied to the surface of zirconia powder, but using CaO as a raw material by forming and baking CaO as a raw material using liquid zirconium chelate as a binder. Is uniformly coated to form a uniform CaO—ZrO ₂ eutectic, thereby preventing melting damage and removing the molten steel adhering to the inner surface at the same time as the modified layer is not peeled off. It is an object of the present invention to provide a metal melting crucible that can provide a quality and a method for producing the same.

In order to solve the above problems, a metal melting crucible according to the present invention is a metal melting crucible mainly composed of calcium oxide (CaO) used in a vacuum melting furnace.
The CaO powder as a raw material is molded and fired using a liquid zirconium chelate as a binder , and CaO—ZrO ₂ eutectic is precipitated on the entire CaO of the aggregate constituting the crucible. CaO is uniformly coated, and a CaO—ZrO ₂ eutectic is formed throughout the crucible molded body .

According to this invention, zirconium is used as a binder for Ca0 as an aggregate in the form of a liquid zirconium chelate, compared to a slurry in which zirconia powder dispersed in ethanol is applied to the crucible surface as in the prior art. Thus, CaO-ZrO ₂ eutectic can be deposited on the entire CaO of the aggregate constituting the crucible, and the progress of melting loss due to the melting temperature at the time of melting of iron of about 1600 ° C. or higher is reliably prevented. can do.
Moreover, since the CaO—ZrO ₂ eutectic is precipitated not over the surface layer as in the prior application technique but over the entire crucible molded body, the mechanical strength is improved and the outer surface is cracked when the CaO crucible is tilted. This can be prevented and the life of the crucible can be extended.

There are two types of zirconium in liquid form: zirconium acylate with a compound of Zr and zirconium chelate in which the periphery of Zr is modified with O and R.
It was experimentally confirmed that a binder based on zirconium chelate was superior in mechanical strength by comparing two types of product forms that were the same liquid but different in compound form.

Moreover, since zirconia (ZrO ₂ ) precipitated from the liquid is an extremely small amount and coats CaO with a small addition amount, and a uniform eutectic is obtained by firing, the progress of melting damage is reliably prevented by a small amount of zirconia. At the same time, the mechanical strength can be improved.

Preferably, a zirconia (ZrO ₂ ) component derived from oxidation of zirconium deposited from the zirconium chelate is contained in an amount of 0.3 to 3% by weight of the crucible fired body.
If it is less than 0.3%, the precipitation of CaO—ZrO ₂ eutectic is reduced, and it is difficult to obtain the effect of preventing melting damage and improving the strength. If it exceeds 3%, the raw material cost increases, so this range is the raw material. An appropriate range is 0.3 to 3% by weight from the viewpoints of cost, prevention of melting damage and improvement of strength.

Preferably, a liquid zirconium chelate is further applied to the surface of the crucible molded body before the firing , and the second CaO—ZrO ₂ co -crystal is further applied to the crucible surface on which the CaO—ZrO ₂ eutectic is precipitated. It is preferable that crystals are deposited .
In this way, after forming CaO powder as a raw material into a liquid zirconium chelate as a binder, liquid zirconium chelate is further applied to the inner surface, outer surface, or both the inner and outer surfaces of the crucible molded body before firing. By applying it, it is possible to easily further improve the strength and prevent melting damage at a place where the strength needs to be improved. The effect can be surely exhibited by firing a crucible coated with a liquid zirconium chelate and precipitating high melting point CaO—ZrO ₂ .

In addition, the method for producing a crucible for melting metal according to the present invention is a method for producing a crucible for melting metal mainly composed of calcium oxide (CaO) used in a vacuum melting furnace.
The CaO powder as a raw material is kneaded and molded using a liquid zirconium chelate as a binder, and then fired to precipitate a uniform CaO—ZrO ₂ eutectic on the entire CaO of the aggregate constituting the crucible. Thus, a crucible molded body in which the CaO is uniformly coated with the precipitated zirconia is manufactured .

According to this invention, zirconium is kneaded and molded using a liquid zirconium chelate in the form of a liquid zirconium chelate, and then fired and manufactured, so that compared to what is applied to the surface layer of zirconia as in the prior application technique, CaO—ZrO ₂ eutectic can be precipitated on the entire CaO constituting the crucible molded body, and it is possible to surely prevent the progress of melting loss due to the melting temperature at the time of melting of iron being about 1600 ° C. or higher. it can.
In addition, since the CaO—ZrO ₂ eutectic is precipitated not over the surface layer as in the prior application technique, but over the entire crucible molded body, the mechanical strength is improved and the ease of cracking of the CaO crucible is improved.

In addition, in the invention of the production method, it is preferable that the zirconia (ZrO ₂ ) component in the zirconium chelate is contained in an amount of 0.3 to 3% by weight of the whole crucible from the viewpoint of raw material cost, prevention of melting damage and strength improvement.

Further, preferably, the liquid zirconium chelate is further applied to the surface of the crucible molded body before firing, followed by firing.
According to such a configuration, after the CaO powder as a raw material is molded using a liquid zirconium chelate as a binder, the liquid zirconium chelate is further transformed into an inner surface, an outer surface, or both the inner and outer surfaces of the crucible molded body before firing. By applying to the surface, it is possible to easily further improve the strength and prevent melting damage at a place where the strength needs to be improved.

According to the present invention, instead of coating the surface of zirconia powder, using liquid zirconium chelate as a binder, CaO is uniformly coated with zirconia deposited from the liquid by molding and firing the raw material CaO, and uniform Crucible for melting metal by forming a strong CaO-ZrO ₂ eutectic so as to prevent melting damage and to remove the molten steel adhered to the inner surface at the same time as the modified layer is not peeled off. And a manufacturing method thereof.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, but are merely illustrative examples. Not too much.

An embodiment of the present invention will be described with reference to FIG.
FIG. 1 shows a procedure for producing a crucible for dissolving metal containing calcium oxide (CaO) (hereinafter referred to as calcia) as a main component.
First, calcia powder as an aggregate is prepared (S1). As the calcia powder, coarse particles having a particle size of 3 to 1 mm, medium particles having a particle size of 1 to 0.3 mm, fine particles having a particle size of 0.3 mm or less, and fine powder of 100 μm are prepared.
Next, a PVP resin (polyvinylpyrrolidone) is added as a binder for maintaining the shape at room temperature as a 10% ethanol solution or powder (S2). Further, zirconium chelate which is liquid organic zirconium is added (S3), and ethanol as a liquid dispersion medium is added (S4). These calcia particles, polymer PVP, zirconium chelate, and ethanol are mixed and kneaded by the kneader 1 (S5).

The distribution ratio of calcia powder is about 20% coarse particles with a particle size of 3 to 1 mm (hereinafter referred to as weight%), about 60% of medium particles with a particle size of 1 to 0.3 mm, and fine particles with a particle size of 0.3 mm or less. When blended in a ratio of 1 to 3 to 1 by weight ratio of about 20%, it is preferable for formability and strength after sintering.
Furthermore, about 100 micrometers fine powder is adjusted with about 1 to 10%, and it is preferable to add about 0.5% of high molecular PVP.
Moreover, it is preferable to contain 0.3 to 3% of zirconium in the whole crucible. If the zirconium content is less than 0.3%, the precipitation of CaO—ZrO ₂ eutectic is small, and it is difficult to obtain the effects of preventing melting damage and improving the strength. If the content exceeds 3%, the raw material cost increases. This is appropriate from the viewpoints of raw material cost, prevention of melting damage and improvement of strength.

Next, the kneaded mixture is flowed into a molding die 8 composed of the core 2, the outer die 4, and the bottom plate 6 to mold the crucible molded body 10 (S6). Thereafter, the crucible molded body 10 is taken out from the mold 8 and dried at 200 ° C. for 1 hour (S 7) and fired at 1600 ° C. for 4 hours (S 8), whereby the crucible fired body 12 constituting the CaO crucible 11 is manufactured. The
In the CaO crucible produced in this manner, zirconia (ZrO ₂ ) precipitated from a liquid zirconium chelate as a binder coats the aggregate CaO and precipitates a uniform CaO—ZrO ₂ eutectic by firing. The small amount of zirconia can surely prevent the progress of melting and improve the mechanical strength.

Moreover, in order to obtain a strong sintered body in order to add, knead and fire zirconia (ZrO ₂ ) in the form of powder, not in liquid form, a high temperature of 2000 ° C. or higher is required, and the height is 50 to For large crucibles of about 60 cm, a large calcining facility is required, which is impossible from the cost point of view. However, by using a liquid zirconium chelate as in the present invention, a 1600 ° C. calcining facility is sufficient. Can be avoided.

Liquid organic zirconium has two forms: zirconium acylate with a compound of Zr and zirconium chelate in which the periphery of Zr is modified with O and R.
As a product form, both of the same liquids but different compound forms were compared, and it was confirmed by a test that a zirconium chelate binder was superior in mechanical strength.

As shown in Table 1, the test was performed using Al chelate, Zr acylate, and Zr chelate, and forming a cylindrical test body having a diameter of 30 mm and a height of 50 mm.
The test composition was the composition shown in the chart of FIG. 2, and the cylindrical body was produced by the method shown in FIG.

FIG. 2 shows the blending components and blending ratios (% by weight) of Comparative Examples 1 to 3 and Examples 1-1 and 1-2. As shown in the figure, in Comparative Example 1, a PVP powder resin binder, an alumina (Al ₂ O ₃ ) chelate organic binder (aluminum ethylene acetoacetate diisopropylate), ethanol, and CaO aggregate Comparative Example 2 is a mixture of a CaO aggregate, a resin binder of PVP powder, an organic binder of zirconia (ZrO ₂ ) acylate (zirconium tributoxy systemate), and ethanol. In Comparative Example 3, PVP powder resin binder, a combined organic binder of ZAl ₂ O ₃ chelate and ZrO ₂ acylate, and ethanol are mixed with CaO aggregate.

In contrast, in Example 1-1, to the aggregate of CaO, and the resin binder in the PVP powder, and ZrO ₂ chelate of an organic binder (zirconium tributoxy acetylacetonate), which was a mixture of ethanol 6.0% ZrO ₂ chelate. Example 1-2 is a mixture of PVP powder resin binder, ZrO ₂ chelate organic binder (zirconium dibutoxybis (ethylacetoacetate)), and ethanol with respect to CaO aggregate. , Containing 5.0% of ZrO ₂ chelate.

2 contains 6.0% and 5.0% of ZrO ₂ chelate, and 12.9% and 13.8% of zirconium in the chelate. As a result, the entire crucible contains zirconium. Shows an example including 0.6 to 0.8%.

As a result of observing the surface of the test piece at the stage of being baked at 1600 ° C. (see FIG. 1) and commercialized, in Comparative Examples 1, 2, and 3, generation of fine cracks and cracks on the surface was observed. This is considered that CaO is hydrated with some moisture.
On the other hand, in each of Examples 1-1 and 1-2, zirconia (ZrO ₂ ) was not hydrated in the form of liquid zirconium chelate, and cracks and cracks were not observed on the surface.

Next, the strength test of the cylindrical test piece will be described.
The strength test of the cylindrical specimen was performed using a compression tester. Furthermore, in order to apply a compressive force of 2000 kg or more on the full load of the compression tester, a hexagon bolt push compression test was conducted. Each result is shown in the chart of FIG.
The test pieces of Examples 1-1 and 1-2 were not broken even at the test load upper limit of 2000 kg of the compression tester. The test pieces of Examples 1 and 2 that did not break were subjected to a hexagonal bolt press compression test consisting of bolts and nuts, and face-pressed with nuts to measure the load until breakage. In addition, it shows in FIG. 4 about the shape of the nut 13 for a hexagon bolt pushing compression test.

From FIG. 3, the stress finally becomes 738.3 (kgf / cm 2) in the test piece of Example 1-1, and 842.3 (kgf / cm 2) in the test piece of Example 1-2. It was confirmed that the stress was significantly improved by about 3 times compared to that of the alumina chelate.
Moreover, it has confirmed that the stress was improving 7 times or more with respect to the comparative example 2 which consists of zirconium acylates.

As described above in Examples 1-1 and 1-2, the CaO—ZrO ₂ eutectic is precipitated over the entire crucible molded body by using zirconium chelate as a binder, instead of modifying only the surface layer as in the prior art. Further, the mechanical strength is improved, and it is possible to prevent the outer surface from being cracked when the CaO crucible is tilted, thereby extending the life of the crucible.

  Next, as a second embodiment, a zirconium chelate liquid is further applied to the surface of the crucible molded body 10 formed according to the first embodiment. That is, the liquid is applied to the surface of the molded crucible molded body 10 between S6 and S7 in the manufacturing procedure shown in FIG. 1, and then dried (S7) and fired (S8).

As shown in FIG. 5, for example, when a zirconium chelate liquid is applied in the direction of arrow P to the crucible inner surface of the crucible molded body 10, zirconia (ZrO ₂ ) in the zirconium chelate liquid that has permeated from the surface penetrates between the CaO particles. The CaO-ZrO ₂ eutectic is precipitated by reacting with the CaO particles. However, since it is a liquid, it can penetrate deeper from the surface as compared with the case of applying a zirconia (ZrO ₂ ) powder slurry.
For this reason, in addition to the modified crucible molded body 10 in Example 1, the strength of the surface layer portion coated with the zirconium chelate can be further improved.

  The zirconium chelate liquid may be applied on the inner surface, the outer surface, or both the inner and outer surfaces of the crucible molded body 10. In order to prevent the outer surface from cracking when the crucible is tilted, it may be applied to the outer surface.

Needless to say, it may be applied together with a zirconia (ZrO ₂ ) powder slurry as in the prior application technique, or may be applied by adding zirconia powder to a liquid zirconium chelate.

  According to Example 2 above, the surface of the crucible molded body 10 formed according to the first example is further coated with a zirconium chelate liquid as needed, thereby further increasing the strength. Improvement and prevention of melting damage can be achieved.

According to the present invention, instead of coating the surface of zirconia powder, using liquid zirconium chelate as a binder, CaO is uniformly coated with zirconia deposited from the liquid by molding and firing the raw material CaO, and uniform By forming a simple CaO-ZrO ₂ eutectic, it is possible to prevent melting damage and to remove the molten steel adhering to the inner surface, and at the same time to obtain a strong modification that does not peel off the modified layer. This is useful in providing a crucible for use and a manufacturing method thereof.

FIG. 3 is an explanatory view showing a procedure for manufacturing the crucible for melting metal of Example 1. 3 is a chart showing the composition of a comparative test of Example 1. 3 is a chart showing the strength test results of Example 1. It is explanatory drawing which shows the nut shape used for the hexagon bolt pushing compression test of an intensity | strength test. FIG. 6 is an explanatory diagram of Example 2. It is explanatory drawing of a prior art. It is explanatory drawing of a prior art. It is explanatory drawing of a prior art.

DESCRIPTION OF SYMBOLS 1 Kneader 2 Core 4 Outer mold 6 Bottom plate 8 Mold 10 Crucible molded body 11 CaO crucible 12 Crucible fired body 13 Hexagon bolt pushing compression test nut

Claims (6)

In a metal melting crucible mainly composed of calcium oxide (CaO) used in a vacuum melting furnace,
The CaO powder as a raw material is molded and fired using a liquid zirconium chelate as a binder , and CaO—ZrO ₂ eutectic is precipitated on the entire CaO of the aggregate constituting the crucible. A crucible for melting metal, characterized in that CaO—ZrO ₂ eutectic is formed over the entire crucible compact by uniformly covering CaO . _2. The metal melting crucible according to claim 1, wherein a zirconia (ZrO2) component precipitated from the zirconium chelate is contained in an amount of 0.3 to 3% by weight of the crucible fired body. The crucible for melting metal according to claim 1, wherein a _second CaO-ZrO ₂ eutectic is further deposited on the surface of the crucible on which the CaO-ZrO ₂ eutectic is deposited . In the method for producing a crucible for melting metal, mainly composed of calcium oxide (CaO) used in a vacuum melting furnace,
The CaO powder as a raw material is kneaded and molded using a liquid zirconium chelate as a binder, and then fired to precipitate a uniform CaO—ZrO ₂ eutectic on the entire CaO of the aggregate constituting the crucible. A crucible molded body obtained by uniformly coating the CaO with the precipitated zirconia is manufactured. The method for producing a crucible for melting metal according to claim 4, wherein the zirconia (ZrO ₂ ) component precipitated from the zirconium chelate is contained in an amount of 0.3 to 3% by weight of the whole crucible. Further, after applying the liquid zirconium chelate to the surface of the crucible molded body before firing, a second CaO- is formed on the surface of the crucible on which the CaO-ZrO ₂ eutectic is deposited. The method for producing a crucible for melting metal according to claim 4, wherein a ZrO ₂ eutectic is precipitated .

Images