The Influence of Continuous Cooling Rate on Nano-Precipitation Behavior of a Ti-Bearing Steel undergone Hot Deformation

The formation of nanoscale precipitates influences the uniform mechanical properties of steels. The precipitation behavior in a Ti-bearing steel with 50% hot deformation is investigated at different continuous cooling rates, including 0.5, 2, and 5 degrees Cs-1. It is found that both the random precipitation and the interphase precipitation are observed in the hot deformed steel by means of transmission electron microscopy (TEM). At the cooling rate of 0.5 and 2 degrees Cs-1, the interphase precipitation and the random precipitation occur even in the same ferrite grain. When the cooling rate is 5 degrees Cs-1, the interphase precipitation disappears and only the random precipitates exist in the small ferrite grains. The morphologies of the interphase precipitation change from the irregular curved type (I-CIP) to regular curved type (R-CIP), and finally to the regular planar type (PIP) with the increase of the cooling rate. The interphase precipitation adjacent to the ferrite grain boundaries reveals its preferential occurrence in the final stage of the transformation. Compared with the isothermal heat treatment, the control of precipitation behavior via cooling rate adjustment is easier and less time-consuming to obtain tailored mechanical properties of the steel.