Review on application of fractal dimension in non-metallic inclusions in steel
Large clusters in steel are formed by collision and aggregation of fine and uniformly distributed solid inclu-sions,which have irregular fractal characteristics.Therefore,the fractal dimension can be used to quantitatively de-scribe the morphology of inclusions.In order to describe the morphology of non-metallic inclusions in steel quantita-tively,the research on the fractal dimension of clustered inclusions is organized.Firstly,the definition and different calculation methods of the fractal dimension,the measurement method of three-dimensional fractal dimension(D3),and the models for the transformation between the three-dimensional and two-dimensional fractal dimensions are summarized.Secondly,the main factors affecting the fractal dimension of inclusions are analyzed,including the composition of inclusions and the calculation error.The fractal dimension of large clusters is about 1.7-1.8.In the process of boxcounting dimension calculation,the calculation error comes from the selection of the maximum size of the covering box.When 0.25≤ε/dmax≤1,the calculation error of inclusion fractal dimension is avoided.Finally,the application of fractal dimension in the study of inclusions is summarized.The theoretical floating velocity of ir-regular clusters in molten steel can be calculated by fractal dimension.The floating velocity of inclusions increases with the increase of fractal dimension.The fractal dimension can be used to study the morphology of aggregates formed by inclusions after collision and aggregation.Based on the development of fractal theory,the diffusion-limit-ed aggregation model(DLA model)is proposed to simulate the aggregation of inclusions in steel.As the distance between the release point of particles and seeds decreases,the particle size increases,and the seed size increases,the aggregation degree of inclusion increases.The stopper or nozzle can be considered as large seeds,and inclusions are easy to gather on its surface,which cause the nozzle clogging.The stopper or nozzle clogging can be reduced by im-proving the wettability between the stopper and inclusions.The aggregated clusters inclusions are in a chain or more dispersed branched structure with the increase of aggregation ratio between the basic particles.The result provides guidance for researching into the collision and aggregation process of clustered inclusions,which facilitates removal fraction by floating to the surface of the molten steel,enhancing the cleanliness of the steel.
fractal dimensioncluster inclusionbox counting dimension methodinclusion floatationcollision and aggregation
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