Nucleation of intragranular ferrite at oxide particles in low carbon steel

The intragranular nucleation phenomena of ferrite in low carbon steels with oxides of CaO and CeO₂ were studied using a method of hot diffusion bonding. The experimental results showed that the fine intragranular acicular ferrite structure in low carbon steels with oxides of CaO and CeO₂ was induced by heterogeneous nucleation of ferrite plates at fine dispersed CaO and CeO₂ particles. There were large thermally induced strain regions in the neighbourhood of CaO and CeO₂. The presence of these regions provided dominant driving force for the nucleation of acicular ferrite, which led to multiple nucleations on the inclusion. Meanwhile a large quantity of new austenite/ferrite high energy interfaces formed, which provided the surface effect of the sympathetical nucleation. The optimum size of oxides for adequate nucleation of acicular ferrite was 0.1 to 0.6μm.