Dislocation Evolution and Inter-Phase Precipitation Behavior of Titanium Microalloyed Hot-Working Die Steel

Grain boundary morphology and dislocation evolution during hot deformation of die steel with and without titanium as well as the size, morphology, distribution, type and the precipitation strengthening mechanism of precipitated phase were studied by means of transmission electron microscope (TEM), high-resolution transmission electron microscope (HTEM), energy dispersive spectroscopy (EDS), etc. The results show that the grain size increases and the dislocation density decreases with the increase of hot deformation temperature. There are three types of nanoscale precipitated phases of titanium-added steel as follows: the first kind is cubic shape TiC precipitated phase, the second kind is spherical VC precipitated phase, and the third kind is associated precipitated phase of Ti and V. The precipitated phase of the titanium-added steel precipitates uniformly and orderly in the interior of the grain, but the precipitated phase of the steel without titanium precipitates in agglomeration and disorderly in the interior of the grain. The size of the precipitated phase of the steel with titanium is 1.1 nm smaller than that of the steel without titanium after hot deformation at 900°C. The precipitated phase sizes of the steel with titanium under 10 nm account for 93% of the total, and the precipitation strengthening effect is significant.