The Main Properties of Magnesia-carbon Bricks

Magnesia-carbon bricks have been widely used in converters, electric furnaces, and ladles due to their excellent high-temperature resistance, slag corrosion resistance, and good thermal shock stability, making them highly suitable for steelmaking requirements. The utilization of carbon materials, which are difficult to wet by slag and molten steel, along with the high refractoriness, high slag resistance, solubility resistance, and low temperature creep properties of magnesia, allows magnesia-carbon bricks to be applied in severely worn areas such as slag lines and ladle mouths. So far, due to the extensive use of magnesia-carbon bricks in steelmaking processes and the improvement of iron and steel smelting technology, significant economic benefits have been achieved. However, magnesia-carbon bricks have shown disadvantages such as high graphite consumption, increased heat consumption, continuous carbon increase in the molten steel, and pollution of the molten steel, resulting in high costs. To reduce raw material costs and obtain clean molten steel, the low-carbonization of magnesia-carbon bricks can effectively address these issues.

The characteristics of magnesia-carbon bricks mainly include the following aspects:

1.Microstructure:

Denseness of Structure: The denseness of magnesia-carbon bricks depends on the types and amounts of binders and antioxidants, the type of magnesia, the particle size, and the addition of graphite. In addition, the molding equipment, brick pressing technology, and heat treatment conditions also have certain influences. To achieve a visible porosity rate of less than 3.0% and ensure a molding pressure of 2t/cm2, it is necessary to use magnesia-carbon bricks with a particle size of less than 1mm for tuyere bricks and ladle mouth bricks. Different binders have certain effects on the denseness of magnesia-carbon bricks, and binders with higher residual carbon rates result in higher bulk densities. The addition of different antioxidants has significantly different effects on the denseness of magnesia-carbon bricks. Below 800 degrees Celsius, the visible porosity rate increases with the oxidation of antioxidants. Above 800 degrees Celsius, the visible porosity rate of non-metallic magnesia-carbon bricks remains unchanged, while that of metallic magnesia-carbon bricks decreases significantly, reaching only half of the rate at 1450 degrees Celsius. Among them, magnesia-carbon bricks containing metallic aluminum have the lowest visible porosity rate.

Heating Rate: The heating rate during the use of magnesia-carbon bricks also affects the change in visible porosity rate. Therefore, when using magnesia-carbon bricks for the first time, it is recommended to increase the temperature slowly to ensure complete decomposition of the binder at a lower temperature. During the use of magnesia-carbon bricks, the impact of temperature difference on the porosity rate is also significant. The greater the temperature difference, the faster the increase in porosity rate.

2.High-Temperature Performance:

High-Temperature Mechanical Properties: The effectiveness of different additives in improving the high-temperature strength of magnesia-carbon bricks varies. Studies have shown that for flexural strength above 1200°C, the sequence is: no additives < calcium boride < aluminum < aluminum-magnesium < aluminum + calcium boride < aluminum-magnesium + calcium boride, with aluminum-magnesium + boron carbide falling between aluminum-magnesium and aluminum-magnesium + calcium boride.

Thermal Expansion Performance: The participation expansion value of magnesia-carbon bricks without added metals is much lower than that with added metals, and the participation expansion value increases with the increase in metal addition.

Anisotropy: The thermal expansion and high-temperature flexural strength of magnesia-carbon bricks vary in different directions due to the orientation of flake graphite. The bricks have higher high-temperature strength and lower thermal expansion in the vertical direction.