Formation of Ultrafine Cellular Microstructure Around Alumina Particles in a Low-Carbon Steel

Ultrafine cellular microstructures around alumina particles in a low-carbon steel were observed, which survived even after cyclic austenitization. This indicates that their formation is closely related to internal stress because of a structural heterogeneity during phase transformation rather than to externally applied forces or deformation. Thermo-elasto-plastic finite element analysis confirmed the evolution of a large hydrostatic pressure around an alumina particle due to thermal mismatch during cooling. Therefore, the fine cellular microstructure might be generated as a result of the hydrostatic pressure, which retards the phase transformation around the particle during cooling. In addition, we observed microstructural similarity with the same steel processed under an ultra-high pressure, which was the evidence for the role of the delay in the transformation caused by the hydrostatic pressure.