When the insulation is started, the molten steel sample is taken with a quartz tube and timed at 0 min, and sampling is repeated at regular intervals. During the test, gas in the molten steel overflowed and burned on the surface of the slag. The carbon content of the steel sample was determined by high-frequency combustion infrared absorption method. The element distribution of the reaction layer between the refractory material and the molten steel was analyzed by using an electron probe with energy spectrum. The microstructure of the refractory material and carbon addition were studied. Effect of the effect. Since the surface of the steel sample was not flat after the experiment, the volume of the steel sample at a certain height was determined using the Archimedean drainage method, and the average thickness of the refractory eroded by molten steel was calculated.
The relationship between the carbon content of different Al2O3C crucible steel samples and the heat treatment time is given. The test results are verified by two repeated tests, the trend of change is exactly the same, and the difference in data changes is within 10%. As can be seen from the figure, the carbon content of the molten steel first increases and then decreases within the time period of 120min of heat preservation; and the raw material components of the Al2O3C crucible with different antioxidants are composed of the raw material components A0/%A1/%A2/%A3/% In 31mm40 fused corundum particle size in 10mm25 particle size less than 0.088mm 2016 graphite 15 metal Al powder 4 metal Si powder 4 SiC powder particle size less than 0.088mm4 resin (external) At the end of the test helium schematic temperature, the final carbon content of all the molten steel is greater than the steel sample The initial carbon content (w(C)=0.002%). The time to reach the maximum carbon content of the steel samples treated in different crucibles was different. In the crucible without antioxidant and SiC anti-oxidant, the maximum value was reached in about 45 min; in the crucible with Si anti-oxidant, the maximum value was reached after 30 min. However, the antimony added to the Al antioxidant additive reaches its maximum value after 20 minutes. At the same time, the highest values ​​of carbon content in different steel samples are also different. The maximum carbon content of molten steel in descending order is as follows: The amount of carbon increased in the medium steel with no added antioxidant is greater than the amount of carbon added when SiC, Si33, and Al are added as antioxidants in the same holding time.
The effect of different antioxidants on the recarburization of molten steel in Al2O3C refractories (16002h) gives the results of the surface scan analysis of the elemental distribution of different lanthanum refractories reaction layers. It can be seen from the figure that helium is added to different anti-oxidants. A decarburization reaction layer caused by reacting molten steel with refractory material has substantially no carbon in this region. The average thickness of the decarburized layer in the crucible without antioxidant was the largest, about 2.83 mm; the average thickness of the decarburized layer in the crucible with the antioxidant Al added was the smallest, about 0.68 mm; it was removed in the crucible with antioxidant Si added. The average thickness of the carbon layer is about 0.91 mm; the average thickness of the decarburized layer in the crucible with the antioxidant SiC added is about 1.42 mm. At the same time, the refractory material is corroded by the molten steel, and the corrosion loss without the antioxidant is about 4.01. Mm; Antimony oxide Al in the tantalum eclipse thickness is about 1.00mm; Antioxidant Si in the tantalum eclipse thickness is about 1.42mm; In antimony SiC antimony added decarburized layer average thickness of about 2.2mm. Corrosion thickness of the material is proportional to the thickness of the decarburization reaction layer, which is mainly due to the dissolution of carbon in the refractory material after the molten steel penetrates, and the refractory material undergoes structural spalling to cause erosion of the refractory material.
EDA analysis of Al2O3C crucible reaction layer with different antioxidants The change trend of carbon content in molten steel is the decarburization effect caused by the recarburization effect of refractories on molten steel (Equation 1) and the transfer of oxygen from the air into molten steel through slag ( Formula 2) caused by the joint. In the early stage of the contact between the molten steel and the refractory, the decarburized layer between the molten steel and the refractory material has not yet formed. The contact area between the graphite and the molten steel in the refractory material is large. According to the formula (1), the carbon directly dissolves into the steel, that is, when the molten steel. Just in contact with the refractory material, a large amount of carbon has been infiltrated into the molten steel before the sampling has been started. In the refractory material, the dissolution rate of carbon in the molten steel is greater than the oxidation rate of carbon in the molten steel, and the carbon content in the molten steel increases. The melting of the steel takes a certain amount of time, so that the carbon content in the first steel sample taken (t=0) is much greater than the original carbon content in the molten steel. With the increase of the holding time, the decarburization reaction layer is formed in the refractory material. The area of ​​contact between the graphite and the molten steel in the refractory material is reduced. The dissolving speed of the carbon in the refractory material into the molten steel is less than that of the carbon in the molten steel. The carbon content gradually decreased. During processing, the refractory material found bubbles emerging from the surface of the slag and forming a blue flame, indicating that the emitted CO was oxidized to CO2 on the surface. The amount of slag added during the test is the same, so it can be assumed that the ability of the air to transfer oxygen through the slag to the steel is the same and the resulting decarburization capacity is the same. Therefore, the difference in the carbon content of the molten steel in the niobium is mainly caused by the difference in antioxidants.
C(s)=(1)2+O2=2CO(g)(2) In contrast, the difference in the carbon content and the maximum carbon content of the molten steel in the four different Al2O3C refractories is mainly due to the resistance of the refractory itself. Steel penetration and erosion resistance. This is because the infiltration of molten steel and the diffusion of dissolved carbon in the molten steel are the controlling steps in the entire recarburization process. The permeation of molten steel is related to the pore size, length and its wettability to the refractory material; the diffusion of carbon in the molten steel is related to the concentration gradient, diffusion coefficient, temperature and other factors. The addition of antioxidants and the chemical reactions that occur at high temperatures can have an impact on the above two aspects and reduce the recarburizing effect of refractory materials on molten steel. The concrete manifestations are: (1) The addition of antioxidants can improve the Al2O3C refractories against molten steel. The resistance to penetration and corrosion resistance, when adding the same quality of antioxidants, Al to improve the resistance of molten steel penetration and corrosion resistance of the refractory material is the largest, followed by Si, SiC is the worst, so in the same holding time, melting The smaller the depth of penetration of steel and the thickness of erosion of refractories, the smaller the effect of refractories on the recarburization of molten steel, and the lower the content of carbon in the molten steel; (2) Dissolution of the antioxidant itself or the reaction products with the surrounding system In molten steel, the viscosity of the molten steel is increased, the diffusion rate of carbon in the molten steel is reduced, and the releasability of the molten steel by the refractory material is reduced; (3) Al, Si, and Al are added when the same mass of antioxidant is added. The density of SiC increases in turn, but is much smaller than the density of corundum. Therefore, in the refractory crucible, the relative volume content of graphite increases sequentially, even if the steel water is refractory Penetration depth of the same material, the total amount of the refractory material of carbon steel by adding Al in the minimum crucible, Si, followed by a maximum without the addition of antioxidants crucible.
Conclusions (1) The effect of carbon-containing refractories on the recarburization of ULC molten steel in air depends on two aspects: on the one hand, the dissolution of carbon in the refractory material into the molten steel; on the other hand, the carbon in the molten steel. Oxidation. When the dissolution rate of carbon in the refractory material to the molten steel is greater than the oxidation rate of carbon in the molten steel, the carbon content in the ULC steel increases, and vice versa. (2) When Al2O3C refractories are added with anti-oxidation additives, they have a certain inhibitory effect on carbon addition to molten steel. When the addition amount is the same, the inhibition effect of Al is the greatest, followed by Si, and the inhibitory effect of SiC is the smallest. (3) The inhibitory effect of carbonation on Al2O3C refractories mainly comes from the fact that the addition of antioxidants enhances the resistance of the refractory to molten steel penetration and erosion resistance, and at the same time it promotes the increase of the viscosity of molten steel and reduces the diffusion rate of carbon in molten steel.
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