CN103936448B - Method for inhibiting desolvation of zirconia metering nozzle stabilizing agent - Google Patents

Abstract

The invention discloses a method for inhibiting the desolvation of a zirconia metering nozzle stabilizing agent. The method comprises the following steps: preparing a ZrO2-Al2O3-MgO composite powder by a gel-sol method; controlling the proportion and granularity of the ZrO2-Al2O3-MgO composite powder, mixing magnesium oxide stabilized zirconia particles and the ZrO2-Al2O3-MgO composite powder in a certain ratio, jointly grinding for 24-28 hours, mixing the jointly-grinded powder, the magnesium oxide stabilized zirconia particles and a proper amount of binding agent, isostatically pressing for molding, drying for 24 hours at 105+/-5 DEG C, and calcining at 1,700-1,720 DEG C to prepare a composite inner layer of the modified zirconia composite metering nozzle, wherein the service life of the composite inner layer can be 33 hours. Residual sample microscopic structure analysis indicates that the number of desolvation of the stabilizing agent is extremely small, and the zirconia particles hardly have phase-change cracking.

Description

A method for inhibiting the desolvation of zirconia sizing nozzle stabilizer

technical field

The invention relates to a process for preparing a material modification for a device for controlling molten steel flow in a continuous casting tundish in the iron and steel metallurgy industry, in particular to a method for inhibiting the desolvation of a zirconia-based sizing nozzle stabilizer.

Background technique

The sizing nozzle refers to a functional device made of high-temperature structural ceramics installed at the bottom of the continuous casting tundish. Its main function is that the static pressure of the molten steel in the tundish remains basically unchanged, the molten steel flows into the crystallizer through the sizing nozzle, and the crystallizer is cooled by a large flow of water to take away the heat released when the molten steel solidifies, so that the molten steel solidifies into a billet. Since the heat taken away by the water cooling of the mold is limited, the amount of molten steel flowing into the mold per unit time must be within a certain range. The larger the aperture of the sizing nozzle, the more the amount of molten steel flowing into the crystallizer per unit time. Select the appropriate aperture to make the tundish nozzle, which is the sizing nozzle. The main reason for the failure of the sizing nozzle is that the heat in the molten steel flow process reacts with the stabilizer in the zirconia, causing the stabilizer to dissolve, which in turn causes the zirconia to become unstable, the particles are exceptional, the strength is greatly reduced, and the erosion resistance is reduced. Expand the diameter, so that the heat released by the solidification of the molten steel flowing into the crystallizer is greater than the heat that the cooling water of the crystallizer can take away, and it is withdrawn from use.

Composite sizing nozzle means that the nozzle is made of two parts of different materials compounded and inlaid. Generally, the outer part is made of lower-priced materials, and the part where the inner layer contacts the molten steel is made of higher-priced materials. Compared with the integral sizing nozzle, the main reason for the compound sizing nozzle is to reduce the production cost without affecting the service life.

The shape of the composite sizing nozzle has not changed much. Pore size is determined by the units used. The key to improving the service life is the improvement of the inner layer material of the inlay.

At present, the integral sizing nozzles produced at home and abroad are mostly made of zircon; the outer material of the composite sizing nozzle is mostly high alumina, and the composite inner layer is made of zirconia, and its zirconia content (wt%) is generally 95%. About, the actual service life is about 10 hours. The main reason for the short service life is the desolvation of the zirconia stabilizer, the stabilizer and other elements in the steel and slag form a low-melting eutectic, the eutectic is lost, the zirconia is unstable, the particles are exceptional, and the strength is greatly reduced. Decreased anti-scouring performance causes diameter expansion, resulting in short service life of the composite inner layer of the composite sizing nozzle.

At present, tundish coatings account for the largest proportion in the contract price per ton of steel for refractory materials used in tundishes, accounting for about 50%. With the digestion of imported technology and the improvement of raw material quality, the current service life of tundish coating has been developed from the original service life of 6-8 hours of silicon insulation board to the service life of 16-20 hours of wet coating materials, and then It has developed into a dry vibration material with a service life of more than 30-40 hours, that is, the service life of the tundish except for the sizing nozzle is more than 30-40 hours, and the sizing service life is about 10 hours. The nozzle has become a bottleneck restricting the service life of the entire tundish.

In order to reduce the production cost per ton of steel in the tundish, a device is added to the part where the sizing nozzle of the tundish is used --- the quick change mechanism of the sizing nozzle of the tundish. After the first sizing nozzle has been used for 6-8 hours, the hydraulic device is used to forcibly slide and push the second nozzle; in this way, the entire tundish can be kept working continuously for more than 30 hours.

The problems brought by the tundish sizing nozzle quick change mechanism are complex production process, complicated equipment structure and operation, increased amount of chromium-containing industrial waste, and increased production cost. In the overall contracting price of tundish steel per ton, only the sizing nozzle quick change mechanism of the tundish accounts for about one-third of the overall contracting price. Therefore, the production of long-life composite sizing nozzles, which is synchronized with the service life of the tundish, is the key to reducing production costs and solving many problems caused by the tundish sizing nozzle quick change mechanism.

Contents of the invention

The purpose of the present invention is to provide a new method for inhibiting the desolvation of the zirconia sizing nozzle stabilizer, and the service life of the zirconia sizing nozzle inner layer prepared by the method can reach more than 30 hours.

In order to realize above-mentioned task, the present invention takes following technical solution:

A process for suppressing the desolvation of semi-stable zirconia stabilizer, characterized in that, it is carried out according to the following steps:

1) Preparation of ZrO ₂ -Al ₂ O ₃ -MgO composite powder

Take ZrOCl ₂ .8H ₂ O by weight percentage to prepare mother liquor, the mother liquor concentration is 0.5-2.0Mol/L, add 1.2% dispersant of the total weight of the material, NH ₄ (OH) positive titration, stir until PH = 7-10, obtained first gel.

Take AlCl ₃ 6H ₂ O by weight percentage to prepare the mother liquor, the mother liquor concentration is 0.5-2.0Mol/L, add 1.2% dispersant of the total weight of the material, NH ₄ (OH) positive titration, stir until PH=8~9, and obtain the first Two gels.

Take MgCl ₂ 6H ₂ O to prepare mother liquor by weight percentage, the mother liquor concentration is 0.5-1.0Mol/L, add 1.2% dispersant of the total weight of the material, NH ₄ (OH) positive titration, stir until PH = 7-9, obtained third gel.

Converted to ZrO ₂ : Al ₂ O ₃ : MgO=(30-50):(40-60):(10-20) by weight percentage to take the first gel, mix and stir the second gel and the third gel, A hybrid gel is prepared.

Aging of the mixed gel for 9h-16h, vacuum suction filtration at -0.095MPa, washing with deionized water until Cl ^- cannot be detected by silver nitrate;

Then react at 500°C for 1 hour, raise the temperature to 700°C, react for 5 hours for degumming, and ball mill for 10 hours after the reaction is completed to obtain ZrO ₂ -Al ₂ O ₃ -MgO composite powder with an average particle size of 1 μm;

2) Take magnesia partially stabilized zirconia particles and magnesia partially stabilized zirconia particles according to the mass ratio of 50:50, wherein the average particle size of magnesia partially stabilized zirconia particles is 0-1mm, and the magnesia partially stabilized zirconia fine powder The particle size composition of the powder is an average particle size of 2-3 μm, D ₅₀ =1.8-2.7 μm, D ₉₀ =4-5 μm.

Take ZrO ₂ -Al ₂ O ₃ -MgO composite powder according to the total mass of magnesia partially stabilized zirconia particles and magnesia partially stabilized zirconia particles fine powder 2%~6%, and compound ZrO ₂ -Al ₂ O ₃ -MgO Powder and magnesia partially stabilized zirconia fine powder are co-milled for 24h~48h to ensure the uniform distribution of ZrO ₂ -Al ₂ O ₃ -MgO composite powder in magnesia partially stabilized zirconia fine powder, and then add magnesia partially stabilized zirconia Granules are mixed with an appropriate amount of binder to prepare a blank, isostatically pressed, dried at 105±5°C for 24 hours, and sintered at a temperature of 1700°C to 1720°C to obtain a composite inner layer of a modified zirconia composite sizing nozzle.

The modified zirconia composite sizing nozzle composite inner layer prepared by the method of the present invention has an alumina content of 1-3%, and a magnesia content of 0.3-0.8% (excluding the magnesia content in magnesia partially stabilized zirconia) ), the bulk density is 5.10-5.30g/cm ³ , and the cold compressive strength is ≥800Mpa. The applicant's trial results show that the service life can reach more than 30 hours.

Description of drawings

Fig. 1 is a flow chart of the preparation process of the composite sizing nozzle of the present invention.

The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments.

Detailed ways

In 2003, the applicant (Xi'an University of Architecture and Technology) undertook the Shaanxi Provincial Industrial Research Project "Development of Baddeleyite Corundum Eutectoid Fine Crystalline High Temperature Ceramics" (Project No. 2003K07-G9), and the Industrial Research Project of Xi'an City, Shaanxi Province "Zirconium Oxide Composite Dispersed Corundum Phase Special High-temperature Ceramics (No. GG200347)"; In 2010, undertook the Jinan Quancheng Scholars Construction Project "Research on ZrO2/Al2O3 Composite Materials and Application in Continuous Casting Functional Materials", and the applicant won the Jinan The honorary title of "Quancheng Scholar"; in 2013, on the basis of the previous research work, undertook the National Natural Science Foundation of China's general project "Study on the Fracture Mechanism and Life Improvement of Zirconia Sizing Nozzle Stabilizer Desolvation Particles" (Project No. 51372193); according to The project undertook to study the damage mechanism of the zirconia sizing nozzle and the research results of improving the service life, and designed a new process to inhibit the desolvation of the semi-stable zirconia stabilizer.

According to the research results, the main process of damage to the zirconia sizing nozzle is that the stabilizer magnesia in the semi-stabilized zirconia has high activity. After the magnesia stabilizer in zirconium is desolvated, the zirconia undergoes a phase transition and cracks, the zirconia particles break, the large particles split into many small particles, the strength of the zirconia sizing nozzle decreases greatly, and the erosion resistance of molten steel and slag Decline, small particles are washed away, causing the diameter of the sizing nozzle to expand and go off the assembly line.

The applicant has studied adding ZrO ₂ -Al ₂ O ₃ composite powder prepared by the sol-gel method to the zirconia sizing nozzle, and the strength and service life of the sizing nozzle are greatly improved. The main mechanism is that ZrO ₂ in the ZrO ₂ -Al ₂ O ₃ composite powder is the original component of the sizing nozzle, and the ZrO ₂ introduced in the composite powder has high activity and is beneficial to sintering. The bulk density and strength of the product are high at the same firing temperature. The amount of Al ₂ O ₃ in the composite powder must be strictly controlled. During the sintering process, Al ₂ O ₃ reacts with the stabilizer MgO extracted from some semi-stabilized zirconia to form magnesium-aluminum spinel, magnesium-aluminum spinel The spar has a high melting point and good corrosion resistance. A wrapping layer is formed around the zirconia particles, which can prevent the stabilizer in the zirconia particles from reacting with molten steel and steel slag, and prevent further precipitation of the stabilizer. After the alumina in the composite powder reacts with the partly stripped stabilizer magnesia to form a magnesia-aluminum spinel coating, the remaining zirconia forms a columnar structure, which further improves the strength of the product. However, it is necessary to strictly control the reaction between the alumina in the composite powder and the partially stripped stabilizer magnesium oxide to form magnesia-aluminum spinel. Experiments have proved that the mass fraction of alumina introduced into the composite powder is 1.5-2.0%, and the effect is the best.

In order to solve the problem of forming a magnesia-aluminum spinel coating around the zirconia particles, preventing the precipitation of the stabilizer magnesia in the zirconia particles from reacting with molten steel and steel slag, and controlling the precipitation of the stabilizer magnesia in the zirconia particles The amount of magnesia-alumina spinel formed with alumina in the composite powder is introduced by introducing a small amount of magnesium oxide into the ZrO ₂ -Al ₂ O ₃ composite powder, and suppressing the stabilizer by adding a small amount of ZrO ₂ -Al ₂ O ₃ -MgO composite powder The desolvation further improves the service life of the sizing nozzle. Through the optimization of the process formula and the actual use of the samples, the effect is good. There is basically no diameter expansion phenomenon when the nozzle is used for more than 30 hours.

In the following examples, the preparation method of the gel is:

Take ZrOCl ₂ .8H ₂ O by weight percentage to prepare mother liquor, the mother liquor concentration is 0.5-2.0Mol/L, add 1.2% dispersant of the total weight of the material, NH ₄ (OH) positive titration, stir until PH = 7-10, obtained first gel;

Take AlCl ₃ 6H ₂ O by weight percentage to prepare the mother liquor, the mother liquor concentration is 0.5-2.0Mol/L, add 1.2% dispersant of the total weight of the material, NH ₄ (OH) positive titration, stir until PH=8~9, and obtain the first two gels;

Take MgCl ₂ 6H ₂ O to prepare mother liquor by weight percentage, the mother liquor concentration is 0.5-1.0Mol/L, add 1.2% dispersant of the total weight of the material, NH ₄ (OH) positive titration, stir until PH = 7-9, obtained third gel.

Technical requirements of raw materials used:

1) The particle size of magnesia partially stabilized zirconia particles is: 0-1mm, that is, 1mm undersize.

2) The particle size composition of the partially stabilized zirconia particles of magnesium oxide is as follows: the average particle size is 2-3 μm, D ₅₀ =1.8-2.7 μm, D ₉₀ =4-5 μm.

3) Binder: 2% cellulose solution.

The following are examples given by the inventors.

Example 1:

Step 1: Prepare the first gel with ZrO ₂ : Al ₂ O ₃ : MgO=50:40:10 by weight percentage, and mix and stir the second gel and the third gel to obtain a mixed gel. The mixed gel was aged for 15 hours, vacuum-filtered at -0.095MPa, washed with deionized water until no Cl ^- was detected by silver nitrate; then reacted at 500°C for 1h, the temperature rose to 700°C, reacted for 5h to degumming, after the reaction was completed Ball milling for 10 hours to produce ZrO ₂ -Al ₂ O ₃ -MgO composite powder with an average particle size of 1.24 μm;

Step 2: Take 5 kg of magnesia partially stabilized zirconia particles and magnesia partially stabilized zirconia fine powder according to the mass ratio of 50:50, and add 0.45 kg of ZrO ₂ -Al ₂ O ₃ -MgO composite powder. The magnesia partially stabilized zirconia fine powder and the ZrO ₂ -Al ₂ O ₃ -MgO composite powder were mixed and co-milled for 36 hours to ensure the uniformity of the ZrO ₂ -Al ₂ O ₃ -MgO composite powder in the magnesia partially stabilized zirconia fine powder distribution, and then add magnesia partially stabilized zirconia particles and 0.5 kg of cellulose solution binder with a concentration of 2%, and mix to prepare a billet.

Step 3, the prepared billet is loaded into a mold, formed by cold isostatic pressing at 230MPa, dried at 105±5°C for 24 hours, and sintered at 1700°C to obtain a composite inner layer of modified zirconia composite sizing nozzle, Its service life can reach 33h. Analysis of the microstructure of the residual sample after use shows that the amount of stabilizer desolvation is very small, and the zirconia particles basically have no phase change fracture.

Example 2:

The difference between this example and Example 1 is: the ZrO ₂ -Al ₂ O ₃ -MgO composite powder in step 1 has ZrO ₂ : Al ₂ O ₃ : MgO=40:45:15, even if ZrO ₂ -Al ₂ The Al ₂ O ₃ /MgO ratio in the O ₃ -MgO composite powder is closer to the theoretical composition of magnesia-aluminum spinel; the ZrO ₂ -Al ₂ O ₃ -MgO composite powder added in step 2 is 4.0%, which guarantees the oxidation The amount of aluminum introduced remains unchanged. The modified zirconia composite sizing nozzle composite inner layer is prepared, and its service life can reach 37h.

Example 3:

The difference between this example and Example 1 is that the sintering temperature in step 3 is adjusted to 1720° C. to obtain a composite inner layer of modified zirconia composite sizing nozzle, and its service life can reach 34 hours.

Claims (3)

1. A method for suppressing the desolvation of zirconia sizing nozzle stabilizer is characterized in that, it is carried out according to the following steps: 1) Preparation of ZrO ₂ -Al ₂ O ₃ -MgO composite powder Take ZrOCl ₂ ·8H ₂ O by weight percentage to prepare mother liquor, the concentration of mother liquor is 0.5-2.0mol/L, add 1.2% dispersant of total material weight, NH ₄ (OH) positive titration, stir until pH=7~10, and obtain first gel; Take AlCl ₃ ·6H ₂ O by weight percentage to prepare mother liquor, the concentration of mother liquor is 0.5-2.0mol/L, add 1.2% dispersant of total material weight, NH ₄ (OH) positive titration, stir until pH=8~9, and obtain second gel; Take MgCl ₂ ·6H ₂ O to prepare mother liquor according to the weight percentage, the mother liquor concentration is 0.5-1.0mol/L, add 1.2% dispersant of the total weight of the material, NH ₄ (OH) positive titration, stir until pH = 7-9, and obtain third gel; Converted to ZrO ₂ by weight percentage: Al ₂ O ₃ : MgO=(30-50):(40-60):(10-20) Take the first gel, mix and stir the second gel and the third gel, Prepare mixed gel; Aging the mixed gel for 9h to 16h, vacuum suction filtration at -0.095MPa, and washing with deionized water until no Cl ^- can be detected by silver nitrate; Then react at 500°C for 1 hour, raise the temperature to 700°C, react for 5 hours for degumming, and ball mill for 10 hours after the reaction is completed to obtain ZrO ₂ -Al ₂ O ₃ -MgO composite powder with an average particle size of 1 μm; 2) Take magnesia partially stabilized zirconia particles and magnesia partially stabilized zirconia particles according to the mass ratio of 50:50, wherein the magnesia partially stabilized zirconia particles have a particle size of 0-1mm, and the magnesia partially stabilized zirconia fine powders The particle size composition is an average particle size of 2-3 μm, D ₅₀ =1.8-2.7 μm, D ₉₀ =4-5 μm; Take ZrO ₂ -Al ₂ O ₃ -MgO composite powder according to the total mass of magnesia partially stabilized zirconia particles and magnesia partially stabilized zirconia particles fine powder, and mix ZrO ₂ -Al ₂ O ₃ -MgO composite powder with The magnesia partially stabilized zirconia fine powder was co-milled for 24h to 48h to ensure the uniform distribution of the ZrO ₂ -Al ₂ O ₃ -MgO composite powder in the magnesia partially stabilized zirconia fine powder, and then the magnesia partially stabilized zirconia particles and A proper amount of binder is mixed to prepare a billet, isostatically pressed, dried at 105±5°C for 24 hours, and sintered at a temperature of 1700°C to 1720°C to obtain a composite inner layer of a modified zirconia composite sizing nozzle. 2. The method according to claim 1, wherein the amount of the binder is 5% of the total mass of the partially stabilized zirconia particles of magnesium oxide and the fine powder of the partially stabilized zirconia particles of magnesium oxide. 3. The method according to claim 2, wherein the binding agent is a 2% cellulose solution.