A critical condition for the formation of a coarse columnar γ grain structure in a peritectic solidified carbon steel

Abstract

The formation of coarse columnar austenite grain (CCG) structure is one of the serious problems in continuous casting processes of peritectic solidified carbon steels.In this study, a guiding principle for avoidance of the CCG formation is developed. The critical condition of the CCG formation recently put forward based on phase-field simulations, which is given by a balance between the cooling condition and the growth rate of the CCG, is first reexamined and modified by considering effect of liquid phase during the CCG formation. Then, the validity of this critical condition is investigated by three different casting experiments combined with heat conduction analyses. From comparison between the cooling conditions and the resulting microstructural changes, the validity of the critical condition is successfully demonstrated.

Experimental Verification of a Critical Condition for the Formation of As-Cast Coarse Columnar Austenite Grain Structure in a Hyperperitectic Carbon Steel

“…The position where the microstructure changes from CCG to EG, which is called transition depth according to Ref. [13], depended on the type of the molds, viz., the cooling a care has to be paid to the following points. The discussion of Ref.…”

“…The discussion of Ref. [13] is based on the assumption that the relation of V T = V CCG is satisfied exactly at the transition depth as long as Eq. (1) is valid.…”

“…The discussion in Ref. [13] accordingly involves uncertainties associated with the non-steady state condition as explained in the next section. The detailed examination of the validity and reliability of the theoretical relationship requires a solidification experiment with a precise control of the steady state cooling condition.…”

“…The cooling condition in the experiments of Ref. [13] was not steady state condition. The discussion in Ref.…”

“…Recently, the validity of the theoretical relationship for the critical condition of CCG formation was investigated by means of the casting experiments [13] . The relation between the cooling condition and the observed microstructural changes were consistent with the theoretical relationship and this fact supports its validity.…”