Precipitation Behavior of FeTiP in Ti-added Interstitial Free High Strength Steels

The precipitation behavior of FeTiP in interstitial free high strength (IFHS) steels has been studied by using a transmission electron microscope (TEM). The results show that the TiC particles, appearing at earlier stage, arc more stable than the FeTiP ones during recrystallization annealing at the two given temperatures (810 degrees C and 840 degrees C). Therefore, the FeTiP particles can only be observed in the steels with sufficient amount of Ti. There is a critical forming time for the FeTiP, which is between 90-120 s at 810 degrees C and 60-90 s at 810 degrees C. The precipitation of FeTiP involves two steps, i.e. the formation of FeTi precursors and the diffusion of P. The former step determines the reliance of Ti content for the precipitation of FeTiP, whereas the latter step leads to the difference in the critical annealing time.