Experiments On Collision And Aggregation Of Non-metallic Inclusions In Liquid Steel

The existence of non-metallic inclusions in steel damages the continuity of steel substrate and greatly affects the mechanical properties of steel. Collision and aggregation of inclusions has significant importance in removal of small inclusions. In this paper, water model and high temperature experiments have been designed to further understand the behaviors of inclusions movement in liquid steel and the mechanism of inclusions collisions and aggregation.Inclusions collisions, aggregation ad flotation in liquid steel were simulated by those of polystyrene plastic particles in sodium chloride solution. The influences of inlet velocity, inlet position, dispersant and temperature on the law of inclusion collision and aggregation are considered. The results show that the changing speed of plastic particle morphology was related to the inlet velocity. The morphology of plastic particle changes slowly, when the inlet velocity is small. Besides, both the morphology of plastic particle and their edge fractal dimension change greatly, when the inlet velocity is large. When the temperature of sodium chloride solution increases from 40℃ to 70℃, the degree of particles collisions increases to a large extent, but decreases as the temperature was over 70℃. The edge fractal dimension value of most individual plastic particle before collision is about 1.2 and the value of aggregation with irregular shape is about 1.3. The edge fractal dimension value of both individual particle and aggregations are independent of the inlet position. Under the same condition of granule number, the bigger the edge fractal dimension value there is, the larger the actually floating velocity appears. With and without surface surfactant, the agglomeration time was 2.61 s and 2.834 s respectively. Under the temperature from 40℃ to 80℃, the average agglomeration time is 1.32 s, which is reduced by 53% compared to room temperature. Besides, an equation of floating velocity of the aggregation, whose equivalent diameter is d, was obtained by fitting,In high temperature experiment, the free cutting steel Y30 and steel 30# were taken as research objects to study the influences of deoxidation method and sulfur content on MnS inclusion, the addition of Ti on the morphology and size of Al2O3 and edge fractal dimension was used to describe the morphology of non-metallic inclusions in steel. It shows that deoxidation method has an obvious effect on the size and morphology of MnS inclusions. After the addition of Al, compound inclusions consisting of Al2O3 and MnS with bigger size and spheroidal shape were formed, and its fractal dimension was about 1.8-1.9. After the addition of Ti, compound inclusions consisting of Al2O3, MnS and TiOx with smaller size and spherical shape were formed, and its fractal dimension was about 1.3-1.4. Sulfur content in steel significantly influenced the morphology of MnS inclusion, when the sulfur content is low, most of the individually precipitated MnS inclusion is spherical and its fractal dimension was about 1.9, when the sulfur content is high, the individually precipitated MnS inclusion is irregular with a little higher fractal dimension,1.95. Addition of Ti has no effects on the morphology of Al2O3. As time passes by, big-size Al2O3 inclusions were formed as the collision and aggregation of small-size Al2O3 inclusions.