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

TL;DR

This study combines microscopy observations and theoretical modeling to investigate pearlite colony formation in eutectoid steels, revealing different mechanisms from non-eutectoid steels and emphasizing the role of interfacial carbon diffusion.

Contribution

It introduces a new theoretical model for pearlite transformation kinetics and compares different carbon diffusion mechanisms, including near grain boundaries, in eutectoid steels.

Findings

Growth instability under volume diffusion mechanism

Steady-state growth via interfacial diffusion

Enhanced diffusion near grain boundaries explains observed features

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.