The industrial objective of lowering the mass of mechanical structures requires continuous improvement in controlling the mechanical properties of metallic materials. Steel cleanliness and especially control of inclusion size distribution have, therefore, become major challenges. Inclusions have a detrimental effect on fatigue that strongly depends both on inclusion content and on the size of the largest inclusions. Ladle treatment of liquid steel has long been recognized as the processing stage responsible for the inclusion of cleanliness. A multiscale modeling has been proposed to investigate the inclusion behavior. The evolution of the inclusion size distribution is simulated at the process scale due to coupling a computational fluid dynamics calculation with a population balance method integrating all mechanisms, i.e., flotation, aggregation, settling, and capture at the top layer. Particular attention has been paid to the aggregation mechanism and the simulations at an inclusion scale with fully resolved inclusions that represent hydrodynamic conditions of the ladle, which have been specifically developed. Simulations of an industrial-type ladle highlight that inclusion cleanliness is mainly ruled by aggregation. Quantitative knowledge of aggregation kinetics has been extracted and captured from mesoscale simulations. Aggregation efficiency has been observed to drop drastically when increasing the particle size ratio.

Populations of inclusions conditioned very early in the alloy production process metals, during the refining and liquid metal treatment stages, are likely to drastically impact mechanical performance, especially fatigue resistance. Control performance of these materials therefore requires control of the inclusion populations, requiring in particular a very good knowledge of the mechanisms which govern their evolution in number and size in refining reactors. Inclusive behaviors in supply chains steel and aluminum have already been the subject of numerical studies at the process scale (Bellot et al., 2014 ; Waz et al., 2016) in which the transport and agglomeration of inclusions are modelled. In order to improve the modelling of key phenomena such as the aggregation and capture of wall inclusions, local simulations, at the scale of an inclusion pair and a layer limit to the wall of a reactor, are carried out here using a lattice Boltzmann method (Sungkorn and Derksen, 2012).

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