EFFECTS OF DYNAMIC AND METADYNAMIC RECRYSTALLIZATION ON MICROSTRUCTURES OF WROUGHT IN-718 DUE TO HOT DEFORMATION

The recrystallized grain size of IN-718 under hot-working conditions is related to the deformation parameters. The high temperature deformation of IN-718 in compression has been studied at temperatures of 950-1100 degrees C over a range of constant strain rates of 0.1, 5 x 10(-2) and 5 x 10(-3) s(-1) using a 200 tonf press. After deformation the material was water quenched. The time interval between the termination of deformation and water quenching was a critical factor in this work. It was found that the dynamically recrystallized grain size increased with increasing temperature and decreasing strain rate under steady state conditions. Metadynamic recrystallization was observed at temperatures of 1050 degrees C and higher with strain rates of 0.1 and 5 x 10(-2) s(-1). The fraction of metadynamic recrystallization increased with increasing strain rate and temperature. An increase in metadynamic recrystallization leads to a relative increase in the recrystallized grain size. This study clarified some of the disputed areas involving the effect of strain rate on the final grain size.