Effect of Nb on the recrystallization of austenite containing high dislocation density

An 18%Ni martensitic steel can revert to austenite by the mode of martensitic shear lattice displacement by rapid heating above the reversion finishing temperature. The reversed austenite is characterized by a high density of dislocations and this highly dislocated austenite causes recrystallization during holding above the reversion temperature. The addition of Nb in solid solution affects the recrystallization of reversed austenite, but it is not so significant when the Nb content in steels is small. It was found that the recrystallization of reversed austenite is retarded in proportion to the amount Nb in solid solution. This is probably attributed to the grain boundary dragging effect by Nb segregated on the grain boundary. On the other hand, the existence of Nb(C,N) precipitates gives a marked retardation effect to the recrystallization of reversed austenite. As a result, it is suggested that the control of Nb(C, N) precipitation is most important to suppress the recrystallization of highly dislocated austenite when the Nb content in steels is low. (AU)