Because magnesium-carbon refractory brick has high slag resistance, thermal shock resistance, high temperature mechanical strength and other characteristics, it is widely used as the lining of steelmaking converter.Although this kind of refractory has been successfully used in steel ladle and furnace lining for more than 20 years, in order to optimize its performance, it is still necessary to conduct in-depth research on its high-temperature performance.
Three kinds of industrial magnesium-carbon bricks (A1, A2 and B bricks) used in steelmaking were selected and evaluated.According to the technical performance provided by the supplier, two different carbon binders are used for this material: asphalt binders (A1 and A2 bricks) and tar binders (B bricks).The relative content of sintered magnesia aggregate and electrofused magnesia aggregate is different, and the content of electrofused magnesia in brick B is higher.Laboratory results confirm these data, as described below
After obtaining the refractory materials from the supplier, the general properties of the refractory materials were tested by various laboratory methods.The crystal phase was determined by X – ray diffractometer and CuK – a diffractometer.The specific gravity density of the powdered sample was determined by kerosene as liquid medium at 37℃.Volume density and porosity were measured according to DIN en 993-1, and true porosity data were obtained.In addition, dta-50 and tga-50 instruments were used to conduct differential thermal analysis and specific gravity analysis.The test was conducted at 1400℃ with heating and cooling rates of 10℃•min-1.The microstructural analysis of all test specimens was carried out by means of optical microscope and scanning electron microscope.In addition, the XL30 scanning electron microscope manufactured by philips can be used for analysis. The pressure is controllable, thermionic tungsten cathode is equipped, and the acceleration voltage is up to 30kV.An energy diffusion analyzer with superfine Si (Li) hole was used for element analysis.Cylindrical specimens (d = 27mm;H =40mm), and obtained the relationship curve between deformation and stress at constant temperature and high temperature.Instron type 8501 servo hydraulic testing machine and SFL type furnace with MoSi2 heater were used in the test.The thermo-mechanical properties were tested at three temperatures: room temperature, 600℃ and 1000℃, and the heating speed was 5℃•min-1. The test was conducted in a controllable atmosphere with inert gas (N2 airflow).The deformation of the sample is measured by a deformometer, which is suitable for measuring high temperature axial deformation (±0.6 microns).During the measurement, a load was applied to the sample at a fixed moving speed of 0.1mm•min-1 until the sample broke.According to the curve data of deformation and stress, the following parameters are determined: tangential elastic modulus (Et);Sigma;Mechanical strength (delta R);The corresponding deformation rate (epsilon f and epsilon R).
The relationship between deformation and compressive stress of industrial mgo-c refractories tested from room temperature to 1000℃ is mainly restricted by the type of carbon binder (asphalt or tar) and its thermal variation.The elastic modulus and mechanical strength of tar binder are higher than that of asphalt binder at normal temperature or high temperature (600℃ and 1000℃).Tar – bonded materials show high hardness and mechanical strength, resulting in brittle fracture.For all samples, the mechanical strength, elastic limit and elastic modulus at 600℃ are all the lowest values, while the parameter that determines deformation is the largest.The low strength of the material at this temperature is due to the change of structure. Such changes occur in the asphalt binder phase and tar binder phase under the action of heat.The hardness and other mechanical properties of mgo-c refractory were restored at 1000℃.At this temperature, the carbon structure was stable in two kinds of materials.Other processes that occur (sintering and chemical reactions) also contribute to the development of such phenomena.