Morphology, orientation relationships and formation mechanism of TiN in Fe-17Cr steel during solidification

Morphology, orientation relationships, and formation mechanism of TiN in Fe-17Cr ferritic stainless steel were investigated theoretically and experimentally by scanning electron microscopy, X-ray diffractometer, and electron backscatter diffraction. Two types of structures of TiN, without cores and with cores, were observed in the solidified microstructure. The dimensionless entropy of fusion (Delta S-m/R) of TiN is calculated as 2.5, which suggests that TiN will exhibit regular faceted morphology. The planar disregistry between (111) plane of TiN and (110) plane of ferrite is calculated as 17.1%, which indicates that it is not sure if TiN can act as the heterogeneous site for ferrite nucleation during solidification. Pole figures of TiN and ferrite by EBSD show that Kurdjumov-Sachs orientation relationship between TiN and ferrite exists, which confirms that TiN can act as the heterogeneous site for ferrite. In addition, based the EDS mapping, TiN in the microstructure should form during solidification rather than solid-state transformation.