Isothermal transformation and precipitation behaviors of titanium microalloyed steels

The microstructure transformation and precipitation behavior of nano-carbides in Ti microalloyed steel during isothermal process were studied by a compression test on a Gleeble 3800 thermomechanical simulator and analyzed by optical microscopy, transmission electron microscopy and other methods. The results show that gamma -> alpha phase transformation and TiC precipitation take place in Ti microalloyed steel during the isothermal process, and time-temperature-transformation curve and precipitation-time-temperature (PTT) curve are all of C-type. During the isothermal process, the interphase precipitation of TiC mostly occurs at the period of the phase transformation, and the random precipitation of TiC mostly occurs on the ferrite after the phase transformation. The increment in yield strength at the initial stage of isothermal transformation mainly comes from phase transformation strengthening. With the increase in isothermal time, the precipitation hardening effect becomes more important for nucleation and growth of titanium carbides and eventually reaches the maximum value at the precipitation finished point of the PTT curve.

Automated summary

The microstructure transformation and precipitation behavior of nano-carbides in Ti microalloyed steel during isothermal process were studied, and it was found that gamma -> alpha phase transformation and TiC precipitation occur during the process. The interphase precipitation of TiC mostly occurs at the period of the phase transformation, while the random precipitation of TiC mostly occurs on the ferrite after the phase transformation. Initial increment in yield strength comes from phase transformation strengthening, and precipitation hardening effect becomes more important with increase in isothermal time, reaching maximum value at the precipitation finished point of the PTT curve.