Abstract
The characteristics of particles greatly affect the microstructure and performance of metallic materials, especially their sizes. To provide insight into coarsening phenomena of particles in metallic melts, Fe-O-Al-Ca melt with calcium aluminate particles was selected as a model system. This study uses HT-CSLM, SEM detections and stereological analysis to probe the behavior of particles and their characteristics including size, number density, volume fraction, spreading of particle size, inter-surface distance and distribution of particles. Based on the experimental evidence and calculation of collision, we demonstrate that the coarsening of inclusion particles is not only dependent on the Ostwald growth as studied in previous study, but also on the particle coagulation, and floatation. The collision of particles affects the maximum size of the particles during whole deoxidation process and dominates the coarsening of particles at later stage of deoxidation under the condition without external stirring in Fe-O-Al-Ca melts. The factors influencing collision behaviors and floating properties were also analyzed, which is corresponding to coarsening behavior and change of particle characteristic in the melts with different amounts of Ca addition. Such coarsening mechanism may also be useful in predicting the size of particles in other metallic materials.
Highlights
Particles are inevitable products in metallic materials which form during metal refining, casting, and thermal processing in liquid or solid metals[1,2,3,4]
In our previous study[36], the experimental evidence for particles size distribution in Fe-O-Al-Ca melt corresponds to the theoretical results based on Ostwald ripening at early stage of deoxidation but not at later stage
The same phenomenon was observed by Hongbin Yin[54], in which they found that the liquid calcium aluminate particles could separate freely after getting in touch with each other at 1/6 seconds
Summary
Particles are inevitable products in metallic materials which form during metal refining, casting, and thermal processing in liquid or solid metals[1,2,3,4]. The Al2O3 particles with high hardness and high melting temperature generate during deoxidation process in Al-killed steels may lead to nozzle clogging[8] Another possible side effect is a decrease in machinability and service life, caused by the nucleation and propagation of voids around precipitate particles on the weak grain boundaries[5,7,9]. It can be concluded that the particle size distribution is effected by nucleation, growth, coagulation due to collision and attractive force, and floatation behavior of particles in liquid metal[47,48,49,50,51,52]. The nucleation and Ostwald ripening of liquid calcium aluminate particles in Fe-O-Al-Ca melt have been investigated in our previous study[36]. This study will provide information to understand the relations between characteristics, behavior and coarsening of particles in Fe-O-Al-Ca melts, and will be helpful for predicting and controlling size of particles
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