The Study On External Addition Method In Oxide Metallurgy

In this thesis,the nano-Ti O2 and nano-Ce O2 were externally added by ball milling pre-dispersion method.Their effects on the microstructure and inclusions,and the corresponding mechanism of intragranular acicular ferrites(IAF)nucleation have been explored by comparison with the direct addition of Ti alloy and rare earth Ce.The aim is to promote the application of external addition method in oxide metallurgy.The conclusions are shown as follows:(1)The thermodynamic calculations show that Ti O2 is unstable in molten steel based on sample's composition;(2)The nano-Ti O2 can be effectively added into molten steel through External addition method.However,the external additions of nano-Mg O and nano-Zr O2 are not effective;(3)The external addition of nano-Ti O2 can engender Ti-bearing inclusion.On the one hand,this method can reduce the inclusion size and increase the inclusion density,On the other hand,Ti-bearing inclusion can induce IAF nucleation and Mn-depletion zone may be the possible mechanism.This is similar to the effect of direct Ti-alloy addition;(4)The external addition of nano-Ce O2 can engender Ce-bearing inclusion.On the one hand,this method can reduce the inclusion size and increase the inclusion density,On the other hand,the Ce-bearing inclusion can induce IAF nucleation and the lattice mismatch may the possible mechanism.This is similar to the effect of direct Ce-alloy addition.