Pinning of austenite grain boundary of Fe-0.09 to 0.53 mass% C-0.02 mass%P alloys by primary inclusions of Ce2O3 and CeS

The effect of the deoxidation and desulfurization products of Ce2O3 (the mean planar diameter, (d) over bar(A)=1.6 to 2.1 mu m) and CeS ((d) over bar(A)=2.2 to 2.8 mu m) particles on the austenite grain growth was studied in Fe-0.20 (0.09 and 0.53) mass%C-0.02mass%P alloys. The melts at 1 873 K were continuously cooled to 1 673, 1 573 and 1 473 K and then were held for 0 to 180 min in the austenite single phase region. Grain growth in the presence of particles was strongly inhibited by the pinning effect and the mean grain size was independent of the carbon content for a given holding time, holding temperature, and Volume fraction of Ce2O3 particles (f(V)=0.08 to 0.12%). The planar limiting grain diameter, (D) over bar(A), obtained at holding times of more than 60 min, was found to be significantly smaller than that predicted from the Zener relation, and the deviation from this relation increased with increasing the (d) over bar(A)/f(v) value. The fraction of particles at the grain boundaries, Phi(A)=0.07 to 0.23, was about 20 to 60 times higher than that estimated from the random distribution from the Zener limit. Based on these Values for Phi(A), the limiting grain size was discussed as a function of f(V) value, and the present results for Ce2O3 and CeS particles were compared with those obtained for the MgO and ZrO2 particles in Fe-0.20 mass%C-0.02 mass%P and Fe-10 mass%Ni alloys.