Effects of Ce and P addition on as-cast structure and formation mechanism of cerium compounds in Ce-added TWIP steels

In TWIP steels, the addition of Ce and P results in the finer as-cast structure which arises from the pinning effect of the Ce-rich compounds against the coalescence of the neighboring columnar grains. Cerium compounds consists of three groups: a multilayered core-shell structure composed of (Ce,Ca)(S,Se), Ce(S,Se,As,P) and CeP, a structure consisting of Ce(As,P) and CeP, and the CeP compound independently formed in the matrix. The Ce(S,Se,As,P), Ce(As,P) and CeP compounds have the same crystal structure as that of the γ matrix which is Fm3−m, while the (Ce,Ca)(S,Se) compound holds a R3−m CeKS2 crystal structure. The orientation of all the cerium phosphides in the core-shell structures are perfectly identical. The formation sequence of the multilayered core-shell structure depends on the binding forces between Ce and X(S,Se,As,P).