Preparation method of thin-strip continuous casting side sealing plate with texture characteristics

Abstract

The invention relates to the field of high-temperature structural ceramics, in particular to a preparation method of a thin-strip continuous casting side sealing plate with texture characteristics. The preparation method comprises the following steps: mixing 60-70% by mass of h-BN, 15-20% by mass of ZrO2, 5-10% by mass of SiC, 5-12% by mass of Al2O3 and 5-12% by mass of Li2CO3, adding a water reducing agent and deionized water, and carrying out ball milling in a ball mill at a rotating speed of 200-300r / min for 4-8h to obtain uniformly dispersed slurry; feeding the slurry into a spray dryer, and drying to obtain powder with the particle size of 100-500 microns; filling the obtained powder into a graphite mold, putting the graphite mold into a hot-pressing sintering furnace, heating, vacuumizing, introducing argon for protection, and carrying out heat treatment; a LiAlSiO4 phase is formed through hot pressing sintering in-situ reaction, the heat conductivity coefficient of the side sealing plate in the thickness direction is reduced in combination with boron nitride textured ceramic, formation of attachments is inhibited in a double-dimension mode, and meanwhile the high temperature resistance, thermal shock resistance, abrasion resistance and erosion resistance of the side sealing plate are guaranteed.

Description

Technical Field

[0001] This invention relates to the field of high-temperature structural ceramics, and specifically to a method for preparing a thin strip continuous casting side sealing plate with textured features. Background Technology In the thin strip continuous casting process, the side sealing plate, as a key sealing component, is subject to extreme conditions such as high temperature (above 1500℃), molten steel scouring, and alternating hot and cold conditions for a long time. Its corrosive working surface (the surface in direct contact with molten steel and slag) is prone to forming island-like deposits.

[0002] Once the attached particles come into contact with the surface of the casting roll, as a hard inclusion, they can easily force the casting roll apart, destroy the stability of the gap between the casting rolls, and thus affect the thickness and surface quality of the strip, and even cause the strip to break and stop casting. Therefore, the harm caused by the side sealing plate attachment falling into the gap between the casting rolls has been upgraded from simple "erosion" and "wear" to "production system disorder". It not only leads to the decline in strip quality and the surge in cost, but also seriously threatens equipment safety and production continuity. This problem has become the core bottleneck restricting production efficiency and casting strip quality. The inventors have conducted an in-depth analysis of the causes of attachment formation: BN-ZrO2-SiC based side sealing plate will undergo the following reaction in the atmosphere of molten steel: 2BN + 3[O] = B2O3(g)↑ + N2(g)↑. The generated bubbles will cause the working layer of the side sealing plate to show an erosion morphology. The attachment of this side sealing plate mainly includes the following three stages: (1) Amorphous phase generation stage: Boron nitride (BN) will be rapidly oxidized and volatilized. The remaining products after oxidation combine with the inclusions in the molten steel to form an amorphous phase; this amorphous phase can act as a mass transfer medium, allowing free oxygen or oxidizing substances ([O], FeO, MnO) to diffuse into the side sealing plate, thus achieving dissolution mass transfer; 2) Dissolution-precipitation stage: the components in the amorphous phase (such as m-ZrO2, SiO2, etc.) will undergo dissolution-precipitation mass transfer, and the crystals such as m-ZrO2, corundum, and spinel will form an attachment growth and enrichment phenomenon; (3) Solid phase skeleton formation stage: coarse-grained crystals such as monoclinic zirconium oxide (m-ZrO2) combine with each other to form a skeleton structure; the amorphous phase fills the gaps in the skeleton, forming an attachment, and most of it exists in the form of solid phase sintering. As the service time of the side sealing plate increases, the attachment continues to sinter and grow, and the risk of its peeling and the resulting hazards become more and more serious.

[0003] Existing technologies cannot fundamentally inhibit the formation of deposits. Therefore, developing a side sealing plate that can block the formation of deposits at the mechanistic level while taking into account comprehensive performance has become the key to breaking through the bottleneck of thin strip continuous casting process. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing side sealing plates that cannot fundamentally solve the problem of deposits. By forming the LiAlSiO4 phase through hot pressing and sintering in situ, and combining it with boron nitride textured ceramics to reduce the thermal conductivity in the thickness direction of the side sealing plate, the formation of deposits is suppressed in two dimensions. At the same time, the high temperature resistance, thermal shock resistance, wear resistance and corrosion resistance of the side sealing plate are guaranteed.

[0005] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: A method for preparing a thin strip continuous casting side sealing plate with textured features, the method comprising the following steps: 1) Mix h-BN, ZrO2, SiC, Al2O3, and Li2CO3 at mass percentages of 60-70%, 15-20%, 5-10%, and 5-12%, respectively. Add water-reducing agent and deionized water, and ball mill in a ball mill at a speed of 200-300 r / min for 4-8 hours to obtain a uniformly dispersed slurry. 2) Feed the slurry into a spray dryer, control the inlet temperature to 180-220℃, the outlet temperature to 80-100℃, and the atomization pressure to 0.3-0.5MPa, and obtain powder with a particle size of 100-500μm after drying; 3) The obtained powder is loaded into a graphite mold, with the inner wall of the mold separated from the powder by graphite paper. It is then placed in a hot-press sintering furnace. Before heating, a vacuum is first applied, with the furnace pressure <1000 Pa. Then, argon gas (purity ≥99.0%, slight positive pressure inside the furnace) is introduced for protection during heat treatment. The lithium carbonate has a particle size <10 μm and a purity ≥97.0 wt%. As a sintering aid, its theoretical melting point is approximately 723℃. Below 1000℃, it can promote the rearrangement and densification of boron nitride flakes, while simultaneously undergoing the chemical reaction: Li₂CO₃ = Li₂O + CO2; SiC + 2CO2 = SiO2 + 2CO; Al2O3 + Li2O + 2SiO2 = 2LiAlSiO4; The theoretical melting point of the formed LiAlSiO4 is about 1400℃, which can further promote the sintering growth and rearrangement of boron nitride nanosheets around the large flakes, making the material texture effect more obvious; At the same time, LiAlSiO4 exhibits a negative coefficient of thermal expansion, which can adjust the coefficient of thermal expansion of the side sealing plate, thereby improving thermal shock resistance; 4) After the blank is cooled in the furnace, it is CNC machined according to the dimensions to finally obtain the ceramic side sealing plate product.

[0006] The heat treatment regime in step 3) is as follows: room temperature - 300℃ for 60 min; 300℃ for 30 min; 300℃-1550℃ and pressure 25~30MPa for 200~300 min; 1550℃ and pressure 25~30MPa for 120~180 min.

[0007] The physical properties of the prepared ceramic side sealing plate products are shown in the table below:

[0008] The water-reducing agent mentioned in step 1) is GLYDOL N1055, accounting for 0.5%-1% of the boron nitride mass fraction; the solid-liquid ratio of the deionized water to the raw material is 1:1.5-1:2.

[0009] The boron nitride is hexagonal and includes two particle sizes, d 50 The particle size is approximately 20μm and d50 is approximately 1μm, with a mass ratio of 5:1 between the two particle sizes. As the main component of the matrix, it has excellent high temperature resistance (melting point of about 3000℃) and good chemical inertness. It can give the side sealing plate base high temperature resistance and resistance to molten steel erosion, while reducing the adhesion between the side sealing plate and molten steel and preventing molten steel from sticking together.

[0010] The zirconium oxide is monoclinic zirconium oxide with a particle size of <3μm, a purity of ≥99.0wt%, a low coefficient of thermal expansion, excellent high-temperature resistance and resistance to molten steel erosion, and good wear resistance.

[0011] The silicon carbide has a particle size of <6μm and a purity of ≥99.0wt%. It has high hardness and excellent wear resistance. As a reinforcing phase, it can significantly improve the normal mechanical properties and hardness of the side sealing plate, and at the same time, it can act as an antioxidant.

[0012] The alumina particles are <5μm in size and have high activity. As a reinforcing phase, it can significantly improve the mechanical strength and hardness of the side sealing plate at both room temperature and high temperature, improve the wear resistance of the side sealing plate, and inhibit plastic deformation at high temperature.

[0013] The present invention proposes a method for preparing a thin strip continuous casting side sealing plate with textured features. By introducing a liquid phase sintering aid, the temperature is reduced by 100-150°C compared to the traditional hot pressing sintering temperature (the existing side sealing plate sintering temperature is about 1700°C). The theoretical melting point of the small amount of LiAlSiO4 phase formed in the prepared side sealing plate is about 1400℃, which is lower than the temperature of molten steel under thin strip continuous casting conditions (1550℃). This low melting point characteristic plays two key roles under high temperature conditions: the reaction products change from "solid adhesion" to "semi-molten flow dynamic". The substances in this semi-molten state no longer have rigid adhesion ability and are easily detached from the working surface and discharged with the flow of molten steel under the action of the scouring force of molten steel (strip drawing speed of about 60m / min) and the rotation force of the casting roll, thus avoiding further sintering and growth; at the same time, LiAlSiO4 will coat the surface of ZrO2 particles, which is equivalent to forming a "liquid isolation layer" between particles: on the one hand, the liquid layer hinders the atomic diffusion between reaction product particles and inhibits grain growth; on the other hand, after the liquid layer fills the gaps between particles, it will not form dense grain boundaries like solid particles. Instead, the fluidity of the liquid phase makes the bonding between particles loose, and it is impossible to form a continuous dense adhesion layer, which weakens the stability of the adhesion from the structure. Meanwhile, hexagonal boron nitride (BN) has a layered crystal structure with high thermal conductivity along the lamellar direction and extremely low thermal conductivity perpendicular to the lamellar direction. This invention prepares boron nitride textured ceramics through pressure-assisted sintering, where the BN grains are oriented along the thickness direction of the side sealing plate, as shown in the figure below. This forms a "layered, superimposed barrier structure" in the thickness direction (pressure direction). When heat is transferred in the thickness direction, it must pass through the weak bonding surfaces between the BN lamellars multiple times, encountering significant thermal resistance. This reduces the thermal conductivity of the side sealing plate in the thickness direction from 15-20 W / (m·K) of existing side sealing plates to approximately 4 W / (m·K), significantly improving its heat preservation performance. The lower temperature gradient makes it difficult for reaction products to form deposits, and the reaction products are more easily corroded into the molten steel. In summary, the low thermal conductivity of boron nitride textured ceramics in the thickness direction and the physicochemical modification effect of LiAlSiO4 on the relative erosion products work synergistically, and the combination of the two greatly improves the anti-adhesion performance of the side sealing plate, which is far superior to the effect of a single technology. Attached Figure Description

[0014] Figure 1 This is a microstructure diagram of the fracture surface of the side sealing plate in a thin strip continuous casting. Detailed Implementation

[0015] The present invention will be described in detail with reference to the accompanying drawings and specific embodiments: Example 1:

[0016] The preparation method of the multiphase ceramic side sealing plate for twin-roll thin strip continuous casting is carried out according to the following proportions:

[0017] According to the proportions in the table, BN with two particle sizes of d50≈20μm and d50≈1μm (mass ratio 5:1), m-ZrO2, SiC, Al2O3 and Li2CO3 mixed powder (molar ratio 1:1) were poured into a stirred ball mill. A water-reducing agent (GLYDOLN1055, accounting for 0.5% of the mass fraction of h-BN) and deionized water (solid-liquid ratio 1:1.5) were then added. The mixture was ball-milled at 300 r / min for 8 hours to obtain a uniformly dispersed slurry. The slurry was then fed into a spray dryer, with the inlet temperature controlled at 220℃, the outlet temperature at 100℃, and the atomization pressure at 0.5 MPa. After drying, powder with a particle size of 500μm was obtained. The obtained powder was loaded into a graphite mold (the inner wall of the mold was separated from the powder by graphite paper), and placed in a hot-press sintering furnace. Upon heating, a vacuum was first applied, with the furnace pressure <1000 Pa. Then, argon gas (purity ≥99.0%, with slight positive pressure inside the furnace) was introduced for protection. The heat treatment regime is shown in the table below. After the green body cooled in the furnace, it was CNC machined to the required dimensions to finally obtain the ceramic side sealing plate product. Example 2:

[0018] The preparation method of the multiphase ceramic side sealing plate for twin-roll thin strip continuous casting is carried out according to the following proportions:

[0019] According to the proportions in the table, BN with two particle sizes of d50≈20μm and d50≈1μm (mass ratio 5:1), m-ZrO2, SiC, Al2O3 and Li2CO3 mixed powder (molar ratio 1:1) were poured into a stirred ball mill. A water-reducing agent (GLYDOLN1055, accounting for 1% of the mass fraction of h-BN) and deionized water (solid-liquid ratio 1:2) were then added. The mixture was ball-milled at 200 r / min for 6 h to obtain a uniformly dispersed slurry. The slurry was then fed into a spray dryer, with the inlet temperature controlled at 200℃, the outlet temperature at 80℃, and the atomization pressure at 0.4 MPa. After drying, powder with a particle size of 300μm was obtained. The obtained powder was loaded into a graphite mold (the inner wall of the mold was separated from the powder by graphite paper), and placed in a hot-press sintering furnace. Upon heating, a vacuum was first applied, with the furnace pressure <1000 Pa. Then, argon gas (purity ≥99.0%, with slight positive pressure inside the furnace) was introduced for protection. The heat treatment regime is shown in the table below. After the green body cooled in the furnace, it was CNC machined to the required dimensions to finally obtain the ceramic side sealing plate product. Example 3:

[0020] The preparation method of the multiphase ceramic side sealing plate for twin-roll thin strip continuous casting is carried out according to the following proportions:

[0021] According to the proportions in the table, BN with two particle sizes of d50≈20μm and d50≈1μm (mass ratio 5:1), m-ZrO2, SiC, Al2O3 and Li2CO3 mixed powder (molar ratio 1:1) were poured into a stirred ball mill. A water-reducing agent (GLYDOLN1055, accounting for 0.6% of the mass fraction of h-BN) and deionized water (solid-liquid ratio 1:1.8) were then added. The mixture was ball-milled at 280 r / min for 6 h to obtain a uniformly dispersed slurry. The slurry was then fed into a spray dryer, with the inlet temperature controlled at 180℃, the outlet temperature at 90℃, and the atomization pressure at 0.3 MPa. After drying, powder with a particle size of 100μm was obtained. The obtained powder was loaded into a graphite mold (the inner wall of the mold was separated from the powder by graphite paper), and placed in a hot-press sintering furnace. Upon heating, a vacuum was first applied, with the furnace pressure <1000 Pa. Then, argon gas (purity ≥99.0%, with slight positive pressure inside the furnace) was introduced for protection. The heat treatment regime is shown in the table below. After the green body cooled in the furnace, it was CNC machined to the required dimensions to finally obtain the ceramic side sealing plate product. .

Claims

1. A method of making a thin strip continuous-casting side-seal plate having textural features, characterized by: The preparation method comprises the following steps: 1) h -BN, ZrO2, SiC, Al2O3, and Li2CO3 are mixed at mass percentages of 60-70%, 15-20%, 5-10%, and 5-12%, respectively. Water-reducing agent and deionized water are added, and the mixture is ball-milled in a ball mill at a speed of 200-300 r / min for 4-8 hours to obtain a uniformly dispersed slurry. 2) the slurry is sent into a spray dryer, the inlet temperature is controlled to be 180-220 DEG C, the outlet temperature is controlled to be 80-100 DEG C, and the atomization pressure is controlled to be 0.3-0.5 MPa, and after drying, powder with a particle size of 100-500 μm is obtained; 3) the obtained powder is loaded into a graphite mold, the inner wall of the mold and the powder are isolated by using graphite paper, and the graphite mold is placed in a hot-pressing sintering furnace, vacuumization is first performed, the pressure in the furnace is less than 1000 Pa, then argon gas (purity is greater than or equal to 99.0%) is introduced to protect the graphite mold in a micro-positive pressure state, and heat treatment is performed; the lithium carbonate has a particle size of less than 10 μm and a purity of greater than or equal to 97.0 wt%, acts as a sintering aid, has a theoretical melting point of about 723 DEG C, and can promote the particle rearrangement and densification of boron nitride flakes below 1000 DEG C, and at the same time, a chemical reaction occurs: Li2CO3=Li2O+CO2; SiC+2CO2=SiO2+2CO; Al2O3+Li2O+2SiO2=2LiAlSiO4; the formed LiAlSiO4 has a theoretical melting point of about 1400 DEG C, can further promote the sintering growth and rearrangement of boron nitride nanosheets around large flakes, and the material texture effect is more obvious; meanwhile, the LiAlSiO4 has a negative thermal expansion coefficient, can adjust the thermal expansion coefficient of the side sealing plate, and thus the thermal shock resistance is improved; 4) after the blank is cooled in the furnace, numerical control machining is performed according to the size, and finally, the ceramic side sealing plate product is obtained.

2. A method of making a thin strip continuous-casting side dam having textural features as claimed in claim 1, characterised in that: In step 3), the heat treatment system is as follows: room temperature-300 DEG C, lasting for 60 min; 300 DEG C, lasting for 30 min; 300 DEG C-1550 DEG C, under a pressure of 25-30 MPa, lasting for 200-300 min; 1550 DEG C, under a pressure of 25-30 MPa, lasting for 120-180 min.

3. A method of making a thin strip continuous-casting side dam having textural features as claimed in claim 1, characterised in that: The water reducing agent described in step 1) is GLYDOL N1055, accounting for Boron nitride 0.5%-1%; the solid-liquid ratio of the deionized water to the raw materials is 1:1.5-1:

2.

4. A method of making a thin strip continuous caster side dam with textural features as claimed in claim 1 characterised in that: The boron nitride is hexagonal and comprises two particle sizes, d 50 ≈20 μm, d50≈1 μm, wherein the mass ratio of the two particle sizes is 5:

1.

5. The method of claim 1 wherein the thin strip continuous-casting side dam plate having textural features is prepared by: The zirconium oxide is monoclinic zirconium oxide, has a particle size of less than 3 μm and a purity of greater than or equal to 99.0 wt%, has a low thermal expansion coefficient, excellent high-temperature resistance and corrosion resistance to molten steel, and good wear resistance.

6. A method of making a thin strip continuous-casting side dam having textural features as claimed in claim 1, characterised in that: The silicon carbide has a particle size of less than 6 μm and a purity of greater than or equal to 99.0 wt%, has high hardness and excellent wear resistance, can significantly improve the mechanical properties and hardness of the side sealing plate as a reinforcing phase, and can also play a role of an antioxidant.

7. A method of making a thin strip continuous-casting side dam having textural features as claimed in claim 1, characterised in that: The alumina has a particle size of less than 5 μm and high activity, can significantly improve the mechanical strength and hardness of the side sealing plate at room temperature and high temperature as a reinforcing phase, can improve the wear resistance of the side sealing plate, and can inhibit plastic deformation at high temperature.

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