Crystallography of the Heterogeneous Nucleation of -Ferrite on Ce2O2S Particles During Solidification of an Fe-4Si Alloy

Crystallographic calculations using the edge-to-edge matching (E2EM) model indicated a high grain refining potency of Ce2O2S for primary delta-ferrite during solidification of associated steels because of the low interatomic spacing misfit of 4.27 pct along the matching directions of < 2 (1) over bar(1) over bar0 > Ce2O2S parallel to| < 110 >(delta-Fe) and the low interplanar mismatch of 4.27 pct between the matching planes of {11 (2) over bar0)Ce2O2S parallel to {011}(delta-Fe). To verify this prediction, an Fe-4Si alloy was selected as the test alloy to enable the retention of the primary d-ferrite at room temperature. The appropriate Ce addition was predicted with thermodynamic calculations using the FactSage Software System based on the sulfur content in the alloy. Compared with that of the alloy without Ce, the addition of 0.0325 wt pct Ce led to a 47.1 pct reduction in the average grain size in the Fe-4Si alloy ingots. Calculations based on the E2EM model also predicted two novel orientation relationships (ORs) between Ce2O2S and the primary d-ferrite. These two ORs were also experimentally observed using electron backscattered diffraction in a scanning electron microscope. The ORs are as follows: [2 (1) over bar(1) over bar0]Ce2O2S parallel to[110](delta-Fe), (000 (2) over bar )Ce2O2S 1.0 deg from (1 (1) over bar0)(delta-Fe), (01 (1) over bar0)Ce2O2S 1.0 deg from (002)(delta-Fe) and [(1) over bar 101]Ce2O2S parallel to[100](delta-Fe), (11 (2) over bar0)Ce2O2S 3.0 deg from (0 (1) over bar(1) over bar)(delta-Fe), ((1) over bar 10 (2) over bar )Ce2O2S 3.0 deg from (0 (1) over bar1)(delta-Fe).