upto – 250 C – precipitation of eta-carbide, partial loss of tetragonality of martensite.
Steels above 0.25 wt% carbon precipitate hexagonal close-packed eta-carbide within the supersaturated martensite until 0.25 wt% carbon level is reached, martensite preserves some tetragonality. The orientation relationship between the laths or rodlets and the cube planes of the matrix was first described by Jack .
200-300 C – decomposition of retained austenite.
200-350 C – replacement of eta-iron carbide by cemeneite,; martensite loses tetragonality
350 C – cementite coarsens and speroidizes, recrystallisation of ferrite.
 Steels 2nd Ed, Honeycombe and Bhadeshia, Edward Arnold, 1981, p172.