The establishment of a safe use system centered on refractory materials has an important impact on the quality and cost of steel and the safe production of steel plants. Therefore, in the application research of refractory materials, many materials scientists analyzed the causes of damage of related refractory materials and gave relevant mathematical models. For example, Akkurt etc. used magnesia carbon bricks for tube furnaces under the protection of argon or CO atmosphere. The slag corrosion resistance test showed that when the time is prolonged, the temperature rises, the oxygen partial pressure in the atmosphere increases and the alkalinity of the slag decreases, the corrosion of refractory materials intensifies, and the degree of slag erosion is related to the rate of carbon loss. Xu Ping studied the influence of factors such as static magnetic field, electromagnetic field, Fe content and carbon content in molten slag on the anti-slag corrosion mechanism of magnesia-carbon refractories. The static crucible method and the induction furnace rotary dipping method were used to study the influence of the amount of β-SiAlON on the slag resistance of MgO-based castables under different alkalinity slag conditions. Research shows that the fractal dimension of the slag corrosion interface morphology of the sample has a linear relationship with its slag erosion resistance. In actual operation, the damage and failure of refractory materials are judged mainly by the experience and habits of on-site technicians. In the actual refining process, the basicity of steel slag changes. At present, the process of ladle refractory changes with service time to failure and dynamic damage remains to be further studied. Therefore, in this work, the effect of steel slag basicity on the erosion rate of magnesia-carbon bricks was studied by the induction furnace rotary dipping method, and the process of damage to magnesia-carbon bricks over time was analyzed, in order to realize the simulation of the damage process of magnesia-carbon bricks. In order to ensure the safe operation of the ladle, reduce the consumption of refractory materials in the ladle, and improve the quality of clean steel, provide practical guidance and theoretical reference.
1 Test
1 1 Sample brick and sample preparation
The sample brick is taken from the trapezoidal magnesia-carbon brick of model YG8 (upper part 180 mmx90 mm, bottom part 160mmx 90 mm, height 230 mm), physical and chemical index: w(C) = 17, bulk density 2.87 g • cm-3, The apparent porosity is 3.73%, and the compressive strength at room temperature is 7.78 MPa. In the laboratory, the magnesia carbon brick was cut into 45 mm x 45 mm x 230 mm specimens with a cutting machine.
1.2 Test process
Clamp the sample to the test machine tool, then add about 15 kg of rebar (brand HRB400) into the induction furnace, turn on the power, preheat for 10 minutes, increase the power to burn until the steel melts, and then weigh them separately two kinds of refined steel slag 20 g were put into the furnace, the power was adjusted, and the surface temperature of the steel slag was measured with an infrared thermometer (model Ircon, ux60P). When the surface temperature
|
Item |
w/% |
|||||||
|
Al2O3 |
TiO2 |
SiO2 |
Fe2O3 |
CaO |
MgO |
MnO2 |
P2O5 |
|
|
Refine Steel Slag 1 |
7.7 |
0.9 |
33.1 |
2.1 |
43.3 |
11.2 |
0.7 |
0.5 |
|
Refine Steel Slag 2 |
2.4 |
1.6 |
13.1 |
38.3 |
28.0 |
9.0 |
5.3 |
2.0 |
Table 1. Chemical composition of two refining steel slags
During the test, 50 g of refined slag was added to the induction furnace every 2 h to keep the composition of the steel slag in the furnace stable and the temperature kept constant. The erosion time was set to 0.5, 1, 1.5, 2, 2.5, 3, and 3.5h.
Fig 1. Schematic diagram of rotary dipping method
1. 3 performance characterization
Taking into account the error during cutting and the uncertainty of the slag line layer, mark A, B, C, and D on the four sides of the sample, measure and record the bottom surface of the four sides with a steel ruler and a vernier caliper. The width at intervals of 1 cm. The damage index is used to characterize the damage degree of the magnesia carbon brick. The damage index is the difference in the width of the sample at the same height before and after the erosion test. For example: when the height of the slag line layer of the sample after erosion is 10 cm from the bottom surface, use the original 10 cm width of the surface A before erosion
Subtract the current eroded width to get the double width of the A side (because the specimen is eroded on both sides of a side at the same time), divide by 2 to get the average width of the A side, that is, the damage index of the A side. Calculate the other 3 faces at 10 cm in turn to get the damage index of the 4 faces, add the sum and divide by 4 to get the average damage index at 10 cm, which is the average damage index at 10 cm.
The damage index. The specific calculation diagram is shown in Figure 2.
Fig 2. Schematic diagram of damage index calculation of specimens
The degree of damage to the sample is represented by the damage index y. Figure 2 shows the height of a certain position from the bottom surface of the sample, H1represents different slag line locations due to different positions, and i represents the surface with different heights i = 1 represents the A side of this height, i= 2 Time represents the B surface of this height, and when 3 and 4 are taken to represent the C and D surfaces respectively), b is the width of the sample before damage, and b' is the width after damage. The calculation formula of damage index is as (1) Shown:
2 Results and analysis
2 1 Erosion analysis
Calculate the damage index at 10 cm of the sample after being corroded by refined steel slag 1 and refined steel slag 2, and make figure 3. At the same time, according to the relationship between the damage index and the erosion time, according to the erosion rate v = ∆y/∆t (∆y is the absolute value of the damage index difference between two consecutive points, and ∆t is the absolute value of the time difference between two consecutive points), each Calculate the erosion rate at two points, and draw the curve in Figure 4 with the value of the erosion rate at two points of the two steel slags corresponding to one point.
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Fig 3 .Damage index of specimens as a function of time
Fig 4. Erosion rate of two kinds of steel slag as a function of time
It can be seen from Figure 3 that the damage index of two kinds of steel slags with different alkalinity to magnesia-carbon bricks shows the same law over time. Both increase first, then stabilize, and then increase again. Refined steel slag with lower alkalinity 1 first Stable at 1.5 h. Comparing the damage indexes of the two steel slags in the same time period, it is found that the damage index of the low basicity refined steel slag 1 is larger than that of the high basicity refined steel slag 2, indicating that the low basicity refined steel slag 1 damages the magnesia carbon brick more seriously .
It can be seen from Figure 4 that at 0.5~1.5 and 2.5~3.5 h, the erosion rate of magnesia carbon bricks with low-basicity steel slag is greater than that of high-basicity steel slag; in 1.5~2.5 h, although the corrosion rate of low-alkalinity steel slag is slightly lower than that of high-basicity steel slag, it can be seen from Figure 3: The stage of 1.5 ~ 2.5 h is the stage where the erosion is relatively stable, while the rate of erosion is lower when <2.5 h The damage index of basicity steel slag is greater than that of high basicity steel slag, indicating that the average erosion rate of low basicity steel slag is greater than that of high basicity steel in the same time.
Scum. This shows that the erosion rate of low-basicity steel slag on magnesia-carbon bricks is greater than that of high-basicity steel slag. The analysis believes that the increase in steel slag basicity increases the content of calcium oxide and magnesium oxide in the steel slag. Calcium oxide and magnesium oxide can neutralize some acidic oxides in magnesia carbon bricks and reduce the saturation of calcium oxide and magnesium oxide in the steel slag, thereby reducing the dissolution of steel slag on the aggregates in the magnesia carbon brick.
From the relationship between the mass ratio of CaO and SiO2 and the phase combination of magnesia refractories, it can be seen that when the mass ratio of CaO and SiO2 in the system is less than 1.87, there will be low melting point substances, and the initial melting temperature will become lower, which will seriously affect The fire resistance of magnesia refractory materials ; when the mass ratio of CaO to SiO ≥1.87, high refractory minerals are generated without significantly reducing the fire resistance. due to
After the carbon in the magnesia-carbon brick is oxidized, the interface between the steel slag and the magnesia-carbon brick forms MgO-CaO-SiO2, which conforms to the mass ratio of CaO and SiO2 of 0.9 3 ～1.87 when low-melting point CMS; CaO and SiO2 mass ratio≥ 1.87, high melting point C2S is formed. The alkalinity of the refining slag 1 is between 0.93 and 1.4, and more low-melting substances are generated, which can promote the dissolution of magnesia particles and accelerate the shedding of magnesia particles.
2.2 Analysis of phase and microstructure
The XRD pattern of the surface at 10 cm of the sample after corrosion by refined steel slag is shown in Fig. 5. It can be seen from Figure 5 that the corrosion of low-alkalinity steel slag on magnesia-carbon bricks does produce low-melting point CMS. The appearance of low-melting point promotes the dissolution of magnesia particles and accelerates the shedding of magnesia particles.
Fig 5. XRD patterns of surface of specimens corroded by refining steel slag
Figure 6 shows the SEM photo of steel slag 1 corroding the magnesia carbon brick sample at 1 cm. It can be seen from Figure 6(a) that the interface between the steel slag and the magnesia carbon brick is very clear, and the steel slag has obvious penetration on the surface of the magnesia carbon brick. This may be due to the pores left by the oxidation of the surface carbon or due to the large pores on the surface that allowed the steel slag to penetrate. It can be seen from Figure 6(b) that the magnesia carbon brick itself is not very dense, and there are large gaps between the particles. The existence of these gaps leaves space for the penetration and erosion of steel slag into the magnesia carbon brick, which accelerates Oxidation of magnesia carbon bricks.
Fig 6. SEM photographs of magnesia carbon brick specimens after erosion
In order to further prove the existence of CMS, take the sample eroded by refining slag 1 at 1 cm for scanning electron microscope observation (see Figure 7) and perform energy spectrum analysis. In the SEM photographs, it is found that the distribution of particles in the erosion area is small and large, cracks appear on the surface of large particles, and the cracks intersect each other. The appearance of cracks connects the erosion area with the outside world, further accelerating the oxidation of carbon. The results of the micro-area energy spectrum analysis (x) of point 1 are: C 46.3 6 %, O 37.41%, Mg 4.0 8%, A1 2.31%, Si 4.83%, and Ca 5.0 1%. It is proved that CaMgSiO4 is generated in the erosion zone.
Fig 7 . SEM photograph of magnesia carbon brick after surface erosion
3 Conclusion
(1) When it is less than 3.5 hours, the erosion rate of low-alkalinity steel slag to magnesia carbon brick is greater; in the same time, the damage index of low-alkalinity steel slag is greater.
(2) Under the conditions of 1.3 and 2.1, the erosion rate of steel slag on magnesia carbon bricks shows the same law, that is, the law of increasing, decreasing, stabilizing and increasing.
(3) Low-alkalinity steel slag generates low-melting point CMS at the erosion interface, and the appearance of low-melting point promotes the dissolution of magnesia particles, thereby accelerating the shedding of magnesia particles.
