Co-Precipitation Behavior in Ferrite Region During Isothermal Process in Ti-Mo-Cu Microalloyed Steel

The coprecipitation of carbides and copper (Cu) particles is an effective technique for strengthening microalloyed steel. In this study, OM and TEM techniques were used to investigate the coprecipitation behavior of carbides and epsilon-Cu in Ti-Mo-Cu microalloyed steel at different isothermal temperatures. A solid solution precipitation model and the classical nucleation theory of precipitates were used to calculate the precipitation kinetics in the Ti-Mo-Cu microalloyed steel. The results show that (Ti, Mo)C and epsilon-Cu precipitated independently, and they showed the N-W and K-S orientations with the ferrite matrix, respectively. The dominant precipitates at 600 degrees C are epsilon-Cu. (Ti, Mo)C and epsilon-Cu were coprecipitated at 620 degrees C. At 640-660 degrees C, (Ti, Mo)C was mainly precipitated in the form of interphase precipitation. Thermodynamic calculations showed that in the range of 600-660 degrees C with an increase in temperature, the Ti/Mo atomic ratio in (Ti, Mo)C increases from 2.5 to 4.5, and the carbide changes from Ti0.71Mo0.29C to Ti0.79Mo0.21C. The precipitation-temperature-time (PTT) curves of (Ti, Mo)C and epsilon-Cu intersect at 616 degrees C, indicating simultaneous precipitation of (Ti, Mo)C and epsilon-Cu. (Ti, Mo)C and epsilon-Cu preferentially precipitate below and above 616 degrees C, respectively. The calculation and experimental results are consistent.