In the steelmaking process, in addition to the long life of the refractory lining of the converter (due to the use of slag splashing to protect the furnace), the life of the refractory lining of the steelmaking electric furnace and the refining ladle is not long, and the life of the refining ladle is even shorter. The service life of most refractory linings mainly depends on the corrosion status of the lining at the slag line. However, magnesia carbon bricks are used as the lining material in most slag line locations. Therefore, in order to improve the service life of the refractory lining, it is necessary to go deep into Understand the erosion process and mechanism of magnesia carbon bricks.
Through scanning electron microscopy, it can be found that the transition layer cannot be observed in non-oxidizing steel slag. This is due to the fact that steel slag cannot corrode graphite. In Figures 1, 2 and 3, the dark gray material is magnesia particles, the white gray material is steel slag, and most of the black material is graphite. From the figure, we can see the erosion depth of magnesia when the slag alkalinity is 1.2 It is about 35μm. When the slag basicity is 1.0, the erosion depth of magnesia is about 280μm. When the slag basicity is 0.8, the erosion depth of magnesia is about 232μm. It can be found that when the basicity is 1.0, the corrosion reaction is the most intense, followed by When the slag basicity is 0.8, the erosion ability is the worst when the slag basicity is 1.2, and it can be seen from the figure that the slag can erode magnesia through the grain boundaries, because the impurities in the grain boundaries are more likely to form low melting point compounds with the slag, and then decompose Erodes the entire magnesia. It can also be found from the figure that the original slag does not directly contact the magnesia over a large area like the previous set of samples, but does not contact or the contact area is very small. This is because the slag basically does not contain highly oxidizing substances. It is difficult for the substances in the slag to oxidize and erode the graphite in the magnesia carbon bricks, causing the slag to penetrate into the gaps of the magnesia carbon bricks and react with the magnesia particles. This process can show the effect of graphite on the non-oxidizing slag from the side. Has strong corrosion resistance. During the entire erosion process, the reaction mainly occurs around magnesia. Then it can be considered that the slag components far away from magnesia are the components of the original slag. Through energy spectrum analysis, we can find several points of slag near magnesia and several points of slag far away from magnesia. Since there is an error in the determination of oxygen atoms by energy spectrum analysis, only the atomic percentage of the element is measured.
The energy spectrum analysis results of the slag far away from the magnesia are basically the same as the original slag. By comparing the changes in the atomic percentages of each element, it can be seen that the composition of the slag after the reaction with magnesia has changed, mainly the atoms of the Mg element in the slag. The atomic percentage of each element increases, and the atomic percentage of each element is shown in Table 2. From this change, it can be inferred that the atomic percentage of Mg element in the slag increases due to the erosion of magnesia by slag. During the static thermal erosion experiment, the original slag and magnesia particles The reaction proceeds to form a low melting point phase and is corroded. Since the magnesia grain boundaries contain various impurities, the slag starts to erode from the magnesia grain boundaries, gradually causing the magnesia to be separated and then slowly eroded.
The main reaction of magnesia being corroded by slag can be derived from the phase diagram of CaO-MgO-SiO2 with an Al2O3 content of 10%. The main component of slag with a basicity of 1.0 is forsterite CMS (CaO·MgO·SiO2) and a large amount of Pseudowollastonite (α-CaO·SiO2), this slag reacts with magnesia to easily form a large amount of low melting point phase forsterite (CMS, melting point is 1490°C), so when the slag basicity is 1.0, the slag The dissolving ability of magnesia is the strongest, which means the erosion ability is the strongest. When the alkalinity of the slag is high, the phase diagram shows that the amount of low melting point phase formed by the slag and magnesia carbon bricks is relatively small, making it harmful to magnesia carbon bricks. The corrosive ability of the slag is greatly weakened. When the alkalinity of the slag is low, the slag will also form a large amount of forsterite with magnesia. In addition, a magnesium silicate MS phase (MgO·SiO2) with a melting point of 1557°C will also be formed. , so when the basicity of the slag is less than 1.0, the slag also has a strong corrosive ability to magnesia.
in conclusion
Under the condition that the non-oxidizing slag basicity is 1.0, the slag can form a large amount of low-melting point material – forsterite CMS (CaO·MgO·SiO2) with magnesia, which leads to its strong corrosion ability towards magnesia; when When the alkalinity is greater than 1.0 and less than 1.0, the melting point of the formed composite oxide becomes higher, which reduces the corrosive ability of the slag, but the slag still has a strong corrosive ability.