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 they gamma matrix which is Fm (3) over barm, while the (Ce,Ca)(S,Se) compound holds a R (3) over barm 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). (C) 2016 Elsevier Inc. All rights reserved.