Experimental and theoretical study of the formation and growth of pearlite colonies in eutectoid steels

Abstract

We describe our optical and electron-microscopy observations of pearlite structures in eutectoid steels which seem to imply that the mechanisms of formation of pearlite colonies in these steels differ from those observed earlier for non-eutectoid steels. A simple theoretical model to study kinetics of pearlite transformations is suggested. Simulations of growth of pearlite colonies based on this model reveal that for the volume carbon diffusion mechanism usually-supposed such growth is always unstable, and the steady-state growth can be realized only via the interfacial carbon diffusion mechanism. A model of formation of pearlite colonies based on the assumption of a strong enhancement of carbon diffusion near grain boundaries is also suggested. The model can be applicable to the plastically deformed steels, and the results of simulations based on this model qualitatively agree with some microstructural features of formation of pearlite colonies observed in such steels.

Towards the ab initio based theory of phase transformations in iron and steel

“…Herewith, there was supposed an acceleration of diffusion on the transformation front. The recent results of phase-field simulations [63][64][65] confirm the necessity of the above assumption. This essential result describes the condition of steady state growth, but it does not concern the problem of nucleation of the pearlite colony, which remains in shadow.…”

“…It should be noted that the mechanism of colony formation in the system with a positive mixing energy (such as the γ phase) is unknown. The proposed approaches considered mostly the evolution of existing colony of alternating plates of ferrite and cementite placed on the flat grain boundary [62][63][64][65]. The model of eutectoid transformation in a system with a symmetric phase diagram was considered in Ref.…”

Heat treatment analysis of multiphase steels through the use of a coupled phase field and finite element model methodology

“…Steinbach and Apel [24] extended this phase field model considering the stress and strain. Vaks et al [25] presented an experimental and numerical study using phase field approach applied to the pearlite in the eutectoid steels. The two principal mechanisms of the eutectoid reaction are, according to the literature, grain boundary diffusion and volume diffusion.…”

Phase Field Study of Microstructure Evolution in Eutectoid Phase Transformation – I Nucleation

“…In 2011 V.G.Vaks et al studied nucleation and growth process of the eutectoid steel, the critical concentration value was obtained according to the relationship between the model and the concentration. The nucleus would be appeared when the concentration is higher than the critical value, the mechanism belongs to the critical undercooling model because the critical concentration value can be converted to the critical degree of undercooling [5]. The formation, nucleation and growth kinetics of ferrite in low carbon high strength steels were studied by Cheng Lin [6] in 2013, and the nucleation mechanism was described based on the experimental results.…”