STUDY OF THE INTERACTION BETWEEN PRECIPITATION AND RECRYSTALLIZATION IN Ti-MICROALLOYED STEELS AFTER REHEATING AT VERY HIGH TEMPERATURE

摘要

The effect of a coarse austenite microstructure on the static recrystallization kinetics and its interaction with strain induced precipitation during hot working has been investigated for two low carbon Ti microalloyed steels. A high reheating temperature of 1460℃ has been used to obtain a large austenite grain size prior to deformation. The interrupted torsion test technique was used to determine the progress of recrystallization with time. It has been observed that when the strain-induced precipitation takes place, the recrystallization curves showed a plateau, denoting the interaction between precipitation and recrystallization kinetics. The beginning and end of each plateau in terms of time have been considered as the precipitation start and finishing times respectively. From these data Precipitation-Time-Temperature curves (PTT) have been built. Transmission electron microscopy (TEM) has been carried out on carbon extraction replicas to study the precipitation before and after the deformation. In the latter, together with Ti(C,N) strain induced precipitates, some fine copper-sulphides have been also identified. These small and fine sulphides have a size of ～20 nm, and they can also exert a retarding effect on recrystallization.