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

Abstract

The effect of the deoxidation and desulfurization products of Ce₂O₃ (the mean planar diameter, d_A=1.6 to 2.1 μm) and CeS (d_A=2.2 to 2.8 μm) particles on the austenite grain growth was studied in Fe-0.20 (0.09 and 0.53) mass%C-0.02 mass%P alloys. The melts at 1873 K were continuously cooled to 1673, 1573 and 1473 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_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_A/f_V value. The fraction of particles at the grain boundaries, Φ_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 Φ_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.