Carbon-free composite ceramic submersed nozzle material and preparation method thereof
阅读说明：本技术 一种无碳复合陶瓷浸入式水口材质及其制备方法 (Carbon-free composite ceramic submersed nozzle material and preparation method thereof ) 是由 陈亚西 于 2019-11-26 设计创作，主要内容包括：本发明公开了一种无碳复合陶瓷浸入式水口材质及其制备方法,属于复合陶瓷技术领域。本发明以硼化铪、氧化锆纤维、硅化铌、氮化硅为原料,采用先后球磨混料、干燥、热压烧结等工艺制备硼化铪-氧化锆纤维-硅化铌-氮化硅复合陶瓷浸入式水口材质,通过先后球磨、在石墨纸和模具内壁涂敷六方氮化硼润滑及添加烧结助剂硅化铌确保了氧化锆纤维-硅化铌-氮化硅复合陶瓷浸入式水口材质的可靠性,此水口同时具有防堵塞和洁净钢水功能。硼化铪-氧化锆纤维-硅化铌-氮化硅复合陶瓷浸入式水口材质致密度高、耐钢水侵蚀、抗氧化、机械强度优异,安装使用过程不易发生断裂,使用可靠性高。此方法工艺简单,生产周期短,适合工业化生产。(The invention discloses a carbon-free composite ceramic submerged nozzle material and a preparation method thereof, and belongs to the technical field of composite ceramics. The invention takes hafnium boride, zirconium oxide fiber, niobium silicide and silicon nitride as raw materials, adopts the processes of ball milling and mixing in sequence, drying, hot-pressing sintering and the like to prepare the material of the hafnium boride-zirconium oxide fiber-niobium silicide-silicon nitride composite ceramic submerged nozzle, ensures the reliability of the material of the zirconium oxide fiber-niobium silicide-silicon nitride composite ceramic submerged nozzle by ball milling in sequence, coating hexagonal boron nitride on graphite paper and the inner wall of a mould for lubrication and adding a sintering aid niobium silicide, and the nozzle has the functions of anti-clogging and liquid steel cleaning. The hafnium boride-zirconium oxide fiber-niobium silicide-silicon nitride composite ceramic submerged nozzle has the advantages of high material density, molten steel erosion resistance, oxidation resistance, excellent mechanical strength, difficult fracture in the installation and use process and high use reliability. The method has simple process and short production period, and is suitable for industrial production.)
1. The utility model provides a carbon-free composite ceramic immersion nozzle material which characterized in that: the carbon-free composite ceramic submerged nozzle is prepared by compositely sintering hafnium boride, zirconium oxide fibers, niobium silicide and silicon nitride, wherein the hafnium boride accounts for 70-87 vol%, the zirconium oxide fibers account for 5-15 vol%, the niobium silicide accounts for 4.5-5 vol%, and the silicon nitride accounts for 3.5-10 vol%.
2. The method for preparing a carbon-free composite ceramic submerged nozzle material of claim 1, wherein the method comprises the following steps: the preparation method of the carbon-free composite ceramic submerged nozzle material comprises the following steps:
① mixing the powder of hafnium boride, niobium silicide and silicon nitride with absolute alcohol, adding ZrO, and ball grinding 2Ball milling is carried out for 3-4 hours under the condition that the rotating speed is 150-180 r/min;
② adding zirconia fiber, continuing to perform secondary ball milling and mixing for 4-5 hours, and obtaining mixed slurry after ball milling is completed;
③ drying the mixed slurry to obtain sintered powder;
④ sintering, coating hexagonal boron nitride on the inner wall of the mold and the contact part of the sintering powder before loading, loading the sintering powder into a graphite mold, and putting the graphite mold into a vacuum hot-pressing furnace for hot-pressing sintering;
wherein the sintering conditions are as follows: heating to 1800-1900 ℃ at a temperature rise speed of 5-20 ℃/min, sintering, keeping the temperature for 60 +/-5 min, and keeping the vacuum degree in the furnace less than or equal to 10 in the whole sintering process -2And Pa, filling argon protective atmosphere, and applying sintering pressure of 20-25 MPa in the sintering process.
3. The method for preparing a carbon-free composite ceramic submerged nozzle material according to claim 2, wherein the method comprises the following steps: the mixing ratio of the ball-milling material to the absolute ethyl alcohol is 1: 1-1: 2.
4. The method for preparing a carbon-free composite ceramic submerged nozzle material according to claim 2, wherein the method comprises the following steps: the ZrO 2The ball-material ratio of the grinding balls to the ball-milling material is 4: 1.
5. The method for preparing a carbon-free composite ceramic submerged nozzle material according to claim 2, wherein the method comprises the following steps: the drying conditions of the dry mixed slurry are as follows: the drying speed is 30-50 r/min, and the temperature is 40-75 ℃.
6. The method for preparing a carbon-free composite ceramic submerged nozzle material according to claim 2, wherein the method comprises the following steps: the hafnium boride accounts for 70-87 vol%, the zirconia fiber accounts for 5-15 vol%, the niobium silicide accounts for 4.5-5 vol%, and the silicon nitride accounts for 3.5-10 vol%.
Technical Field
The invention belongs to the field of composite ceramic materials, and particularly relates to a carbon-free hafnium boride-zirconia fiber-niobium silicide-silicon nitride composite ceramic submerged nozzle material and a preparation method thereof.
Background
Hafnium boride (HfB) 2) Is gray crystals with metallic luster, belongs to a hexagonal structure, and the boron atom planes and the hafnium atom planes in the crystal structure are alternatedThe ionic bond between the boron atom surface and the hafnium atom surface and the strong bond property of the boron-boron covalent bond determine the high temperature resistance (the melting point is 3380 ℃) of the hafnium boride, the strength is high at normal temperature and high temperature, the thermal shock resistance is good, the hafnium boride is oxidation-resistant at high temperature, the chemical stability is good, and the hafnium boride is hardly corroded by acid and alkali (except hydrofluoric acid).
CN201410234517.7 provides a preparation method of a tungsten-aluminum nitride-hafnium boride composite material, which comprises the following steps: firstly, mixing and ball-milling mixed powder of tungsten powder, aluminum nitride powder and hafnium boride powder with absolute ethyl alcohol according to a proportion to obtain slurry; drying and grinding the slurry to obtain a blank; thirdly, carrying out hot-pressing sintering on the blank to obtain the tungsten-aluminum nitride-hafnium boride composite material. According to the invention, the aluminum nitride is introduced into the composite system of tungsten and hafnium boride, so that the room temperature fracture toughness of the composite material can be improved, the sintering temperature can be reduced, the sintering temperature of the composite material can be further reduced through mechanical alloying, and the separation between a ceramic phase and a metal can be avoided. The tungsten-aluminum nitride-hafnium boride composite material prepared by the method has good matching performance of room temperature fracture toughness and high temperature tensile strength.
The application numbers are: 201811177542.0, a carbon fiber reinforced hafnium boride-tantalum boride-carbon ceramic matrix composite and a method for preparing the same are provided. The method comprises the following steps: (1) dipping a carbon fiber preform by using a hafnium-tantalum precursor solution containing a hafnium-tantalum precursor copolymer, a boron source precursor, a carbon source precursor and an organic solvent, and then sequentially carrying out curing and cracking on the dipped carbon fiber preform; and (2) repeating the step (1) for a plurality of times to prepare the carbon fiber reinforced hafnium boride-tantalum boride-carbon ceramic matrix composite material. The preparation method has the advantages of simple process, no need of any additive, low preparation temperature, short preparation period, easy industrial implementation and the like. The carbon fiber reinforced hafnium boride-tantalum boride-carbon ceramic-based composite material prepared by the method has the advantages of good toughness, ultrahigh temperature resistance, excellent oxidation resistance, excellent ablation resistance and the like.
Submerged entry nozzle (submerged nozzle) is a refractory casing for pouring in a continuous casting plant installed at the bottom of a tundish and inserted below the level of the steel in a crystallizer. The main function of the submerged nozzle is to prevent secondary oxidation of the pouring flow of the tundish and molten steel splashing; the covering slag of the crystallizer is prevented from being involved into the molten steel; the flow state and heat flow distribution of the injection flow in the crystallizer are improved, so that the uniform growth of a billet shell in the crystallizer is promoted, and the elimination of gas and inclusions in steel is facilitated. The submerged nozzles have remarkable effects on improving the quality of casting blanks, improving labor conditions, stabilizing continuous casting operation, preventing surface defects of the casting blanks and the like, so that the submerged nozzles are adopted for casting in slab continuous casting and bloom continuous casting in various countries in the world.
The basic requirements of the submerged nozzle material are good molten steel melting loss resistance, strong slag erosion resistance and good thermal shock resistance. The commonly used materials are fused silica and Al 2O 3-two species C. The submerged nozzle is made of fused quartz as raw material and is formed by slurry casting and high-temperature sintering. The nozzle has small heat conductivity coefficient (2W/m.K at 1000 deg.C), good thermal stability, and low thermal expansion rate (such as 99% SiO content) 2The expansion rate of the quartz at 1000 ℃ is 0.05-0.06%), the quartz is not easy to form nodules, and the quartz can be used without preheating. The fused quartz nozzle is not suitable for casting steel with manganese content more than 0.5 percent because of SiO in the Mn nozzle 2Reaction to generate MnO.SiO with the melting point of only 1300 DEG C 2The glass reduces the viscosity of the glass layer on the surface of the water gap and accelerates the melting loss of the water gap.
Al 2O 3the-C submerged nozzle is formed by taking corundum and graphite as basic raw materials, adding metal silicon, silicon carbide and the like, forming in an isostatic press and then performing protective sintering, and is suitable for pouring most steel grades.
Al 2O 3Before the-C nozzle is used, graphite burning loss (decarburization) occurs in the preheating process, so that the porosity of the surface layer of the nozzle is increased, and the corrosion resistance of the surface layer of the nozzle is reduced. Al in casting special steels and Al or Al-Si killed steels 2O 3-C immersion nozzle tends to produce Al 2O 3The accretion phenomenon causes unstable flow state of molten steel, even the nozzle is blocked, which damages normal casting flow and affects the quality of steel billets. In Al 2O 3-C basisZrB developed above 2-Al 2O 3The oxidation resistance of the-C nozzle material is greatly improved, but the problem of nozzle blockage is still not solved. Al (Al) 2O 3-C nozzle Al 2O 3One of the main causes of clogging is the presence of carbon in the nozzle material, and SiO therein 2Reduction reaction is carried out, and the reduced SiO and CO further react with Al in the molten steel to produce Al 2O 3Al adhered to the inner wall surface of the nozzle 2O 3On the aggregate, Al on the inner wall of the nozzle 2O 3And (6) depositing. Therefore, the non-carbonization of the material of the submerged nozzle is one of the methods for solving the problem of nozzle blockage, and the literature, "research and application of non-carbon raw materials in steelmaking process" indicates that the material of the submerged nozzle has various advantages of non-carbonization.
The hafnium boride can be used as a high-speed cosmic arrow material and can be used in the atmosphere of 2000-2200 ℃, and the oxidation resistance of the boron compound containing much hafnium is 10 times higher than that of zirconium boride. The hafnium boride has high strength at normal temperature and high temperature, good thermal shock resistance, oxidation resistance at high temperature, good chemical stability and almost no acid-base corrosion, and meets the requirements of good molten steel corrosion resistance, strong slag corrosion resistance and good thermal shock resistance of the submerged nozzle material.
The submerged nozzle material has excellent thermal shock resistance, high fracture toughness and thermal shock resistance, which means more use times, long service life and excellent use reliability. Therefore, the hafnium boride ceramic used as a submerged entry nozzle must be further improved in thermal shock resistance, fracture toughness and thermal shock resistance to increase its competitive advantage. In addition, the carbon-free hafnium boride ceramic nozzle material has the functions of preventing blockage and cleaning molten steel.
Single hafnium boride ceramic (bending strength less than or equal to 400MPa, compressive strength about 1555.3 MPa, elastic modulus about 343GPa, fracture toughness less than or equal to 3.5 MPa.m 1/2) The thermal shock resistance, the erosion resistance, the thermal shock resistance and the fracture toughness of the hafnium boride ceramic are limited, and the comprehensive mechanical strength of the hafnium boride ceramic is difficult to meet the mechanical strength requirement required by a nozzle brick, so that the preparation process and the formula of the hafnium boride ceramic must be improved, and the hafnium boride ceramic can be used as an immersion nozzle. At present, ChinaThe introduction of a second phase into a ceramic matrix has been used by internal and external researchers to improve thermal shock resistance, fracture toughness and thermal shock resistance. However, experiments show that simply adding the second phase does not effectively improve the performance, but rather reduces the performance if the design is not reasonable.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provide a carbon-free hafnium boride-zirconia fiber-niobium silicide-silicon nitride composite ceramic submerged nozzle material and a preparation method thereof.
The invention provides a carbon-free composite ceramic submerged nozzle material which is prepared by compositely firing hafnium boride, zirconium oxide fiber, niobium silicide and silicon nitride, wherein the hafnium boride accounts for 70-87 vol%, the zirconium oxide fiber accounts for 5-15 vol%, the niobium silicide accounts for 4.5-5 vol%, and the silicon nitride accounts for 3.5-10 vol%.
The preparation method of the carbon-free composite ceramic submerged nozzle material comprises the following steps:
① mixing the powder of hafnium boride, niobium silicide and silicon nitride with absolute alcohol, adding ZrO, and ball grinding 2Ball milling is carried out for 3-4 hours under the condition that the rotating speed is 150-180 r/min;
② adding zirconia fiber, continuing to perform secondary ball milling and mixing for 4-5 hours, and obtaining mixed slurry after ball milling is completed;
③ drying the mixed slurry to obtain sintered powder;
④ sintering, coating hexagonal boron nitride on the inner wall of the mold and the contact part of the sintering powder before loading, loading the sintering powder into a graphite mold, and putting the graphite mold into a vacuum hot-pressing furnace for hot-pressing sintering;
wherein the sintering conditions are as follows: heating to 1800-1900 ℃ at a temperature rise speed of 5-20 ℃/min, sintering, keeping the temperature for 60 +/-5 min, and keeping the vacuum degree in the furnace less than or equal to 10 in the whole sintering process -2And Pa, filling argon protective atmosphere, and applying sintering pressure of 20-25 MPa in the sintering process.
Further, the mixing ratio of the ball-milling material to the absolute ethyl alcohol is 1: 1-1: 2.
Further, the ZrO 2The ball-material ratio of the grinding balls to the ball-milling material is 4: 1.
Further, the drying conditions of the dry mixed slurry are as follows: the drying speed is 30-50 r/min, and the temperature is 40-75 ℃.
Advantageous effects
The hafnium boride is of a hexagonal structure, a two-dimensional network structure is formed by the alternate appearance of boron atom surfaces and hafnium atom surfaces in the crystal structure, the ionic bond between the boron atom surfaces and the hafnium atom surfaces and the strong bond property of a boron-boron covalent bond determine the high temperature resistance (the melting point is 3380 ℃) of the hafnium boride, the strength of the hafnium boride is very high at normal temperature and high temperature, the hafnium boride is good in thermal shock resistance and oxidation resistance at high temperature, the hafnium boride has good chemical stability and is hardly corroded by acid and alkali, and the requirements of good molten steel corrosion resistance, strong slag corrosion resistance and good thermal shock resistance of a submerged nozzle material are met. In addition, the material does not contain carbon and SiO 2And has the functions of preventing blockage and cleaning molten steel. However, the related use of the hafnium boride-based submerged nozzle is not reported in China.
The denser the material of the water gap, the more excellent the erosion resistance and the erosion resistance in the continuous casting process. The hafnium boride grains are connected by strong covalent bonds, atoms diffuse slowly during sintering, and are difficult to sinter and densify, so that the hafnium boride is not suitable for being produced by adopting the traditional nozzle preparation process technology of slurry casting molding. The hot-pressing sintering method can reduce the porosity and improve the density and the mechanical property of the material, thereby being an ideal method for preparing the hafnium boride ceramic for the submerged nozzle.
Although hafnium boride having a large hafnium content is excellent in oxidation resistance, it is necessary to add a small amount of additives in order to further improve its high-temperature oxidation resistance. At present, adding silicide is one of the methods for improving the oxidation resistance of hafnium boride. At high temperature, a hafnium oxide and borosilicate glass dense oxide film layer is generated on the surface of the hafnium boride material added with silicide, so that external oxygen can be prevented from entering the material to be further oxidized.
Zirconium oxide (ZrO) 2) The fiber can be used for a long time in the ultrahigh temperature oxidizing atmosphere above 1500 ℃ and the highest using temperatureCan maintain intact fiber shape up to 2200 deg.C, even to 2500 deg.C, and has a tetragonal phase (t-ZrO) 2) To monoclinic phase (m-ZrO) 2) The martensitic transformation effect of (2). Thus, the introduction of the second phase ZrO in the hafnium boride ceramic 2The fiber can simultaneously achieve the effects of fiber toughening and phase change toughening. In addition, the normal temperature thermal conductivity of the zirconia is 4.0W/m.K, and the thermal conductivity of the material of the nozzle is slightly reduced by introducing the zirconia at 1000 ℃ of 2.09W/m.K.
When hot-pressing sintering is adopted, the length of the zirconia fiber can be partially damaged due to overlarge pressure, and the toughening mechanism of fiber debonding, pulling-out and bridging is weakened, so that a small amount of sintering aid needs to be added to reduce the sintering temperature and pressure. The melting point of niobium silicide is 1940 ℃, and the niobium silicide can generate a borosilicate glass compact oxide film layer with hafnium boride to improve the oxidation resistance of the borosilicate glass compact oxide film layer, so the niobium silicide is the best sintering aid for preparing the zirconium oxide fiber toughened hafnium boride-based ceramic by a hot pressing method.
The friction factor of the silicon nitride is 0.02-0.35, and the silicon nitride is equivalent to the surface of the oiled metal, so that the silicon nitride has excellent self-lubricating capability. It has excellent chemical stability, and can resist all inorganic acids except hydrofluoric acid and most non-metal solution. In addition, it can resist cold and hot impact, and can be heated to above 1000 deg.C in air, and can be cooled rapidly and heated rapidly, and will not be broken. Therefore, when the hafnium boride ceramic is added into the hafnium boride ceramic, the friction coefficient can be reduced, the molten steel scouring resistance is improved, and the thermal shock resistance are improved.
The hexagonal boron nitride has a melting point of 3000 ℃, has a layered structure similar to graphite, has good lubricity, is coated on the inner wall of the grinding tool to reduce the friction force between particles and the inner wall of the grinding tool, is beneficial to uniform distribution of pressure in a blank so as to reduce density difference of each part, ensures that the material has reliable mechanical property, and simultaneously reduces diffusion of carbon elements in the graphite into the blank.
The drying of the invention adopts a rotary evaporation drying method, the rotating speed and the temperature of the rotary evaporation dryer are properly controlled, and if the rotating speed is too low and the drying is not sufficient, the centrifugal force is too high to cause the gravity segregation.
The invention relates to hafnium borideThe hafnium boride-zirconia fiber-niobium silicide-silicon nitride composite ceramic submerged nozzle material has the apparent porosity of less than or equal to 8 percent, the bending strength of more than or equal to 450MPa, and the fracture toughness of more than or equal to 6.28 MPa.m.m. 1/2The highest thermal shock resistance temperature △ T can reach 1400 ℃, the molten steel erosion resistance is less than or equal to 0.62mm/h, the thermal shock resistance frequency is more than or equal to 50 (1100 ℃, water cooling), the spalling resistance is less than or equal to 18.7 percent, and the thermal expansion coefficient is less than or equal to 6.67 multiplied by 10 -5K -1. The invention adopts the process method, takes hafnium boride, zirconia fiber, niobium silicide and silicon nitride as raw materials, and adopts the processes of ball milling, mixing, drying, hot-pressing sintering and the like to prepare the hafnium boride-zirconia fiber-niobium silicide-silicon nitride composite ceramic submerged nozzle.
The carbon-free composite ceramic submerged nozzle prepared by the process has the advantages of high material density, molten steel erosion resistance, oxidation resistance, excellent mechanical strength, difficult fracture in the installation and use process and high material use reliability. The method has simple process and short production period, and is suitable for industrial production.
Detailed Description
The present invention will be described in detail with reference to specific examples.
In the embodiment of the invention, the average grain diameter of the hafnium boride powder is less than or equal to 5 mu m, and the purity is more than or equal to 99 percent; ZrO (ZrO) 2The diameter of the fiber is 5-10 μm, and the length is 100-500 μm; the average grain diameter of the niobium silicide powder is less than or equal to 10 mu m, and the purity is more than or equal to 99 percent; the average grain diameter of the silicon nitride powder is less than or equal to 5 mu m, and the purity is more than or equal to 99 percent. The average grain diameter of the hexagonal boron nitride for lubrication is respectively less than or equal to 20 mu m, and the purity is more than or equal to 99 percent;
- 上一篇：一种医用注射器针头装配设备
- 下一篇：一种高纯度超细高熵陶瓷粉末及其制备方法