Magnesia-carbon core nozzle

Abstract

This invention belongs to the field of refractory materials technology, and relates to a magnesia-carbon core nozzle raw material composition and mass percentage as follows: 55-70% magnesia aggregate with a particle size of 1-0.047mm, 15-30% magnesium titanate with a particle size <0.047mm, 9-12% flake graphite with a particle size of 0.1-0.3mm, 2-3% carbon fiber powder with a particle size <0.047mm, and 1-3% antioxidant with a particle size <0.047mm; the bonding system of the magnesia-carbon core nozzle consists of phenolic resin powder, lithium carbonate, and furfural; after the raw materials and bonding system are mixed and granulated in a high-speed mixer, the billet is dried and the volatile matter is controlled appropriately, then added to the core nozzle mold for medium static pressure molding, and after demolding, the billet is cured and then heat-treated; during the heat treatment process, the magnesia aggregate and the magnesium titanate as the matrix are... m MgO· n TiO2 fine powder undergoes a solid-phase reaction, MgO+ m MgO· n TiO2→ x MgO· y TiO2, where 0.5 < x / y ≤2, magnesium oxide aggregate diffuses into the matrix through solid-phase diffusion, forming reactive annular gaps. This invention improves the mechanical properties and thermal shock resistance of the material.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of refractory materials, and particularly relates to a magnesium-carbon core nozzle suitable for thin strip continuous casting. BACKGROUND

[0002] The thin strip continuous casting process is short and has low carbon emission, and is a development frontier of the steel industry. The core nozzle is a key refractory material in the thin strip continuous casting process, plays an important role in stabilizing the flow field and temperature field of the double-roll molten pool, and avoids contaminating the molten steel (low dissolution) and molten pool slagging. The casting process of high-quality strip steel puts forward higher requirements for the corrosion resistance, dissolution and stability of the key refractory material. Based on the adjustment of high-quality casting parameters, especially the reduction of the pulling speed, higher requirements are put forward for the service life of the core nozzle. The core nozzle experiences two thermal shocks during service. Due to the complex structure and stress concentration during thermal shock, the local part is prone to peeling and even cracking. Therefore, in order to ensure the thermal shock resistance, the current core nozzle material uses a relatively high carbon content (about 15wt%). Carbon is easy to diffuse and dissolve into molten steel, which is not conducive to the corrosion resistance of molten steel, and restricts the service life, especially the escape of carbon oxide in the form of gas, which causes the surface flow field of the molten pool to be turbulent. Therefore, the low-carbon content and high-thermal shock-resistant material and the outer shape structure meet the higher requirements of the new process of the thin strip continuous casting for the corrosion resistance, low dissolution and high reliability of the core nozzle. One of the main reasons for the defects of the cast strip is the existence of Al2O3 and MgO·Al2O3 high-melting-point inclusions. The conventional core nozzle material mainly includes spinel-carbon (CN 110090946 B) and zirconium-carbon (CN 111168050 A). The aluminum-magnesium core nozzle forms corundum or spinel inclusions in the cast strip due to corrosion. The stable zirconia used in the zirconium-carbon core nozzle is easy to desorb, which leads to the instability of zirconia and the cracking of zirconia into molten steel.

[0003] The magnesium-carbon refractory material has excellent properties such as high-temperature resistance, resistance to molten steel scouring and resistance to molten steel corrosion, and is currently widely used in the rod head part of the stopper. It can form a dense magnesium oxide enrichment layer on the working surface under service conditions, thereby realizing low dissolution characteristics. The most important performance of the core nozzle is thermal shock resistance. The thermal expansion coefficient of MgO is large (13.5 x 10 -6 / ℃ -1 , 20-1000 ℃), so the thermal shock resistance of the magnesium-carbon material is greatly different from that of other carbon-containing refractory materials, thereby limiting its application as a core nozzle material. SUMMARY

[0004] The purpose of the present application is to provide a magnesium-carbon core nozzle, which has a low thermal expansion coefficient, excellent thermal shock resistance, and can significantly improve the corrosion resistance of molten steel and avoid causing high-melting-point inclusions such as alumina and spinel.

[0005] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0006] A magnesium-carbon core nozzle, raw material composition and mass percentage are as follows: 55-70% of magnesia aggregate with particle size of 1-0.047mm, 15-30% of magnesium titanate with particle size of <0.047mm, 9-12% of flake graphite with particle size of 0.1-0.3mm, 2-3% of carbon fiber powder with particle size of <0.047mm, and 1-3% of antioxidant with particle size of <0.047mm; the binding system of the magnesium-carbon core nozzle is composed of phenolic resin powder, lithium carbonate and furfural; the adding amount of the phenolic resin powder is 7%-9% of the total weight of the raw materials of the magnesium-carbon core nozzle; the adding amount of the furfural is 110%-120% of the weight of the phenolic resin powder; the lithium carbonate is 1%-1.5% of the weight of the phenolic resin powder; after the raw materials and the binding system are mixed and granulated in a high-speed mixer, the blank is dried and the appropriate volatile matter is controlled, and then the blank is added into a core nozzle mold for medium static pressure forming, and after demolding, the blank is solidified and then heat treated, and the heat treatment atmosphere is N2; during the heat treatment process, the magnesia aggregate and the magnesium titanate as the matrix generate solid phase reaction, the magnesia aggregate around the matrix diffuses into the matrix to form a reaction annular gap, and the magnesium-carbon core nozzle needs to be preheated and baked at 1200 DEG C in a weak oxidizing atmosphere for 2 hours before use, at which time the TiO2 formed by the oxidation of the titanium powder, titanium nitride or titanium carbide is further solid-solved into the original matrix system, that is, TiO2 + MgO· TiO2 reaction occurs, the binding strength of the oxidation layer is improved, the magnesium-carbon core nozzle plays a role of antioxidant during pouring of molten steel, and the oxidation of graphite or bonded carbon is slowed down. m MgO· n TiO2 fine powder, MgO + m MgO· n TiO2 → x MgO· y TiO2, wherein 0.5 < x < 2, the magnesia aggregate around the matrix diffuses into the matrix to form a reaction annular gap; the magnesium-carbon core nozzle needs to be preheated and baked at 1200 DEG C in a weak oxidizing atmosphere for 2 hours before use, at which time the TiO2 formed by the oxidation of the titanium powder, titanium nitride or titanium carbide is further solid-solved into the original matrix system, that is, TiO2 + MgO· TiO2 reaction occurs, the binding strength of the oxidation layer is improved, the magnesium-carbon core nozzle plays a role of antioxidant during pouring of molten steel, and the oxidation of graphite or bonded carbon is slowed down. x / y x MgO· y TiO2 → u MgO· v TiO2 reaction, the binding strength of the oxidation layer is improved, the magnesium-carbon core nozzle plays a role of antioxidant during pouring of molten steel, and the oxidation of graphite or bonded carbon is slowed down.

[0007] The magnesia aggregate is fused magnesia or sintered magnesia, and MgO > 98.0wt%.

[0008] The chemical formula of the magnesium titanate is m MgO· n TiO2, which is an artificial synthetic material, and MgO and TiO2 are mixed and pressed according to a ratio (1≤x≤2) and then prepared by a sintering process, and then the product is crushed and ground into 200-mesh fine powder. m / n

[0009] ​​The carbon fiber powder is one or more of M series carbon fibers, such as M40, M46, and M50.

[0010] The anti-oxidant is one or two of titanium metal powder, titanium carbide powder, and titanium nitride powder.

[0011] The isostatic pressing pressure is 30-50 MPa, and the pressure holding time is 1-5 minutes.

[0012] The heat treatment temperature is 1200-1400 DEG C, and the holding time is 1-3 hours.

[0013] The uniform gap on the surface of the magnesia aggregate can significantly reduce the thermal expansion coefficient of the material and improve the thermal shock resistance of the material, and does not affect the performance of the material, which can be proved by theoretical calculation.

[0014] Assuming that the magnesia particle with a particle size of 1 mm is a uniform sphere, the thermal expansion coefficient of the magnesia is 13.5*10 -6 / ℃, the temperature change is 20-1000 DEG C, and the linear expansion of the 1.0 mm particle is: Delta L = 1.0*(1000-20)*13.5*10 -6 = 0.013 mm = 13 mu m, thus it is inferred that the 10-micron annular gap (20-micron length) on the surface of the 1.0 mm particle can completely buffer the particle expansion, thereby avoiding the adverse effects of the magnesia particle on the thermal shock resistance of the core nozzle.

[0015] The high-modulus carbon fiber powder is also introduced in the application, and since it shrinks after being heated (the thermal expansion coefficient is negative), the thermal expansion coefficient of the core nozzle material can also be reduced.

[0016] The titanium metal powder introduced in the application can form a ceramic-based bond under a nitrogen atmosphere (Ti + N2→ TiN), which can enhance the mechanical properties of the magnesia-carbon core nozzle and improve the oxidation resistance of the material.

[0017] The lithium carbonate contained in the combined system of the application can reduce the graphitization transition temperature of the phenolic resin, improve the graphitization degree, and thus improve the oxidation resistance of the bonding phase.

[0018] The magnesia-carbon core nozzle provided by the application has excellent resistance to molten steel erosion and scouring, and through in-situ solid-phase reaction of the matrix and the aggregate, annular gap expansion joints are formed on the edges of the magnesia aggregate, a small amount of high-modulus carbon fiber is introduced to further reduce the thermal expansion coefficient of the material, and thus the thermal shock resistance of the magnesia-carbon core nozzle is improved, the mechanical properties and oxidation resistance of the material are improved by the composite bonding (titanium nitride and resin carbon), and finally a new type of magnesia-carbon core nozzle is obtained.

[0019] The application is compared with the performance (typical value) of spinel core nozzle

[0020] Density / g-cm -3 ]] 2.63 2.55 Apparent porosity / % 18.0 16.2 Cured billet strength / MPa 8.5 5.0 Coefficient of thermal expansion, room temperature - 1000°C / *10 -6 ]] 4.5 4.0

[0021] Therefore, as can be seen from the above, the application adopts magnesia material to avoid pollution of molten steel or formation of high-melting-point inclusions, reduces the thermal expansion coefficient by forming aggregate interstices in situ, and improves the mechanical properties and thermal shock resistance of the material by introducing ceramic reinforcement technology, which has obvious innovation and wide application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The microstructure of the core nozzle after oxidation treatment. DETAILED DESCRIPTION

[0023] The application will be described in detail in combination with the drawings and specific examples: Example 1

[0024] First, the main component materials of the core nozzle are weighed according to the proportions described in the table below, then 9% of phenolic resin powder of the total weight of the above raw materials and 1.5% of lithium carbonate of the total weight of the phenolic resin powder are weighed together, and are mixed in a high-speed mixer for 10 minutes, then 120% of furfural of the total weight of the phenolic resin powder is poured in, and is mixed again for 5 minutes, then it is sieved through a 50-mesh sieve, then the blank is dried at 60°C, then the blank is poured into a mold, and is formed in an isostatic press, with a maximum pressure of 30 MPa and a pressure holding time of 5 minutes, the blank is solidified and heat treated in an N2 atmosphere at a temperature of 1200°C for 3 hours, and after processing, a magnesia-carbon core nozzle is obtained.

[0025] Main component materials of the core nozzle

[0026] raw material granularity Added amount fused magnesia 1-0.047mm 70 m MgO· n TiO2]]> ​ <0.047mm 22 Flake graphite 0.1-0.3mm 12 M40 <0.047mm 1 M46 <0.047mm 2 Titanium powder <0.047mm 1 Titanium carbide powder <0.047mm 2 Example 2

[0027] First, the main component materials of the core nozzle are weighed according to the proportions described in the table below, then 7% of phenolic resin powder of the total weight of the above raw materials and 1% of lithium carbonate of the total weight of the phenolic resin powder are weighed together, and are mixed in a high-speed mixer for 10 minutes, then 110% of furfural of the total weight of the phenolic resin powder is poured in, and is mixed again for 5 minutes, then it is sieved through a 50-mesh sieve, then the blank is dried at 60°C, then the blank is poured into a mold, and is formed in an isostatic press, with a maximum pressure of 50 MPa and a pressure holding time of 1 minute, the blank is solidified and heat treated in an N2 atmosphere at a temperature of 1300°C for 2 hours, and after processing, a magnesia-carbon core nozzle is obtained.

[0028] Main component materials of the core nozzle

[0029] raw material granularity Added amount fused magnesia 1-0.047mm 58 m MgO· n TiO2]]> ​ <0.047mm 30 Flake graphite 0.1-0.3mm 9 M60 <0.047mm 2 Titanium powder <0.047mm 0.5 Titanium nitride powder <0.047mm 0.5 Example 3

[0030] The main component materials of the core water gap were weighed according to the proportions described in the following table, and then the total weight of 8% phenolic resin powder and 1.2% lithium carbonate of the total weight of the phenolic resin powder were weighed together in a high-speed mixer for 10 minutes, then poured into 115% of the total weight of the furfural of the total weight of the phenolic resin powder, mixed again for 5 minutes, passed through a 50 mesh sieve, then the blank was dried at 60°C, then the blank was poured into a mold, molded in an isostatic press with a maximum pressure of 40Mpa and a pressure holding time of 1 minute, the blank was heat treated in an N2 atmosphere at a temperature of 1400°C for 1 hour, and after processing, a magnesium-carbon core water gap was obtained.

[0031] Main component materials of the core water gap

[0032] raw material granularity Added amount fused magnesia 1-0.047mm 69 m MgO· n TiO2]]> ​ <0.047mm 15 Flake graphite 0.1-0.3mm 11 M40 <0.047mm 1 M46 <0.047mm 1 M50 <0.047mm 0.5 Titanium powder <0.047mm 0.5 Titanium carbide powder <0.047mm 1 Titanium nitride powder <0.047mm 1

Claims

1. A method for using a magnesium-carbon core nozzle, characterized in that: Before use, the magnesium-carbon core water nozzle needs to be preheated and baked at 1200℃ in a weak oxidizing atmosphere for 2 hours. The raw material composition and mass percentage are as follows: 55-70% magnesium oxide aggregate with a particle size of 1-0.047mm, 15-30% magnesium titanate with a particle size <0.047mm, 9-12% flake graphite with a particle size of 0.1-0.3mm, 2-3% carbon fiber powder with a particle size <0.047mm, and 1-3% antioxidant with a particle size <0.047mm. The bonding system of the magnesium-carbon core water nozzle consists of phenolic resin powder, lithium carbonate, and furfural. The amount of phenolic resin powder added is the same as the original amount of the magnesium-carbon core water nozzle. The total weight of the raw materials is 7% to 9%; the furfural content is 110% to 120% of the weight of the phenolic resin powder; the lithium carbonate content is 1% to 1.5% of the weight of the phenolic resin powder; the antioxidant is one or two of metallic titanium powder, titanium carbide powder, and titanium nitride powder; after the raw materials and the bonding system are mixed and granulated in a high-speed mixer, the billet is dried and the volatile content is controlled appropriately, then added to the core sprue mold for isostatic pressing, and after demolding, the billet is cured and then heat-treated in an N2 atmosphere; during the heat treatment process, the magnesium oxide aggregate and the magnesium titanate as the matrix are mixed and granulated around the magnesium sand aggregate. m MgO· n TiO2 fine powder undergoes a solid-phase reaction, MgO + m MgO· n TiO2 → x MgO· y TiO2, where 0.5 < x / y ≤2, magnesium oxide aggregate diffuses into the matrix through solid phase diffusion, forming a reaction ring gap.

2. The method of using a magnesium-carbon core inlet as described in claim 1, characterized in that: The magnesium oxide aggregate is fused magnesia or sintered magnesia, wherein MgO > 98.0 wt%.

3. The method of using a magnesium-carbon core inlet as described in claim 1, characterized in that: The chemical formula of the magnesium titanate is: m MgO· n TiO2 is a synthetic material, made by mixing MgO and TiO2 in a ratio (1≤ m / n ≤2) Mix and press into blocks and prepare by sintering, then crush and grind into 200 mesh fine powder.

4. The method of using a magnesium-carbon core inlet as described in claim 1, characterized in that: The carbon fiber powder is one or more of the M-series carbon fibers, such as M40, M46, and M50.

5. The method of using a magnesium-carbon core inlet as described in claim 1, characterized in that: The isostatic pressing pressure is 30-50 MPa, and the pressure is held for 1-5 minutes.

6. The method of using a magnesium-carbon core inlet as described in claim 1, characterized in that: The heat treatment temperature is between 1200℃ and 1400℃, and the temperature is maintained for 1 to 3 hours.

Images