Recrystallization and Sigma Phase Formation as Concurrent and Interacting Phenomena in 25%Cr-20%Ni Steel

Recrystallization kinetics of an austenitic steel containing nominally 25%Cr and 20%Ni has been investigated mainly by optical and transmission electron microscopy. The activation energy for recrystallization was found to be 4.6×105 J/mol which was excessively greater than the values previously observed in steel. It was surmised that a sigma phase formation accompanied the recrystallization phenomenon, and that this transformation acted as a barrier for growth of recrystallized grains. It is proposed that the sigma phase formation and recrystallization are concurrent and interacting phenomena and hence the activation energy described above is considered to be a sum of those for recrystallization, 2.3×105 J/mol, and for diffusion of chromium atoms, 2.3×105 J/mol, governing the sigma phase formation.