Strain-induced Precipitation in Ti Micro-alloyed Interstitial-free Steel

Stress relaxation method was carried out on a Ti micro-alloyed interstitial-free(IF)steel at the temperature ranging from 800 to 1 000℃.The results show that the softening kinetics curves of deformed austenite can be divided into three stages.At the first stage,the stress has a sharp drop due to the onset of recrystallization.At the second stage,aplateau appears on the relaxation curves indicating the start and finish of strain-induced precipitation.At the third stage,the stress curves begin to descend again because of coarsening of precipitates.Precipitation-timetemperature(PTT)diagram exhibited a"C"shape,and the nose point of the PTT diagram is located at 900 ℃ and the start precipitation time of 10 s.The theoretical calculation shows that the strain-induced precipitates were confirmed as almost pure TiC particles.The TiC precipitates were heterogeneously distributed in either a chain-like or cell-like manner observed by transmission electron microscopy(TEM),which indicates the precipitates nucleated on dislocations or dislocation substructures.In addition,a thermodynamic analytical model was presented to describe the precipitation in Ti micro-alloyed IF steel,which shows a good agreement between the experimental observation and the predictions of the model.