TiN/γ-Fe interface orientation relationship and formation mechanism of TiN precipitates in Mn18Cr2 steel

A Mn18Cr2 steel containing TiN precipitates was fabricated by vacuum induction melting. The morphology of TiN precipitates and the interface orientation relationship between TiN and γ-Fe were characterized by means of SEM, TEM and SAED, and the formation mechanism of TiN precipitates in Mn18Cr2 steel was clarified. Results show that the TiN precipitates are more likely to exhibit a cubic-shaped morphology and form both within the grain and at the grain boundary of γ-Fe. The interface orientation relationship between TiN and γ-Fe is determined as follows: $${(100)_{{\rm{TiN}}}}//{(1\bar 11)_{{\rm{\gamma}} - {\rm{Fe}}}},\,\,{[0\bar 11]_{{\rm{TiN}}}}//{[\bar 112]_{{\rm{\gamma}} - {\rm{Fe}}}}$$ . Because of the smallest interfacial misfit, the secondary close-packed lane {100} of TiN preferentially combines with the close-packed plane {111} of γ-Fe during the precipitation in order to minimize the interface energy. After nucleation, the TiN precipitates exhibit cubic appearance due to the fact that the TiN has a FCC structure with rock salt type structure. This study provides reference for the material design of the austenitic high-manganese steels with excellent yield strength.