A Coupled Thermodynamic Model for Prediction of Inclusions Precipitation during Solidification of Heat-resistant Steel Containing Cerium

A coupled thermodynamic model of inclusions precipitation both in liquid and solid phase and microsegregation of solute elements during solidification of heat-resistant steel containing cerium was established. Then the model was validated by the SEM analysis of the industrial products. The type and amount of inclusions in solidification structure of 253MA heat-resistant steel were predicted by the model, and the valuable results for the inclusions controlling in 253MA steel were obtained. When the cerium addition increases, the types of inclusions transform from SiO2 and MnS to Ce2O3 and Ce2O2S in 253MA steel and the precipitation temperature of SiO2 and MnS decreases. The inclusions CeS and CeN convert to Ce2O3 and Ce2O2S as the oxygen content increases and Ce2O3 and CeN convert to Ce2O2S, Ce3S4, and MnS as the sulfur content increases. The formation temperature of SiO2 increases when the oxygen content increases and the MnS precipitation temperature increases when the sulfur content increases. There is only a small quantity of inclusions containing cerium in 253MA steel with high cleanliness, i.e., low oxygen and sulfur contents. By contrast, a mass of SiO2, MnS and Ce2O2S are formed in steel when the oxygen and sulfur contents are high enough. The condition that MnS precipitates in 253MA steel is 1.2w[O] + w[s]>). 01% and SiO2 precipitates when 2w[O]+w[s]>0.017% (w[S]<0.005%) and w[O]>0. 006% (w[S]>0. 005%).