Hetero-epitaxial nucleation of ferrite at a TiN encapsulating MgAl2O4 during rapid solidification in a newly developed ferritic stainless steel

The mechanism for the promoted formation of equiaxed ferrite grains during rapid solidification has been investigated in the gas‑tungsten arc welds of a newly developed ferritic stainless steel. The preferential nucleation of ferrite at the interface of TiN encapsulating MgAl2O4 spinel compound was observed in the developed steel showing a higher potential to form TiN-MgAl2O4 complex inclusions. The epitaxial alignment of 110ferrite//311_TiN and 011_ferrite//022_TiN was first found, which is different from Kurdjumov-Sachs, Nishiyama-Wasserman and Baker-Nutting relationships. The faceted interfaces to keep the epitaxy is energetically favored, which may reduce the activation barrier for the formation of ferrite. A finite element model calculation of heat transfer was used to examine the role of heterogeneous nucleants as well as the local thermal condition. The developed steel is predicted to have 1.4 times more heterogeneous nucleants than the conventional steel.