[Paper Review] Autocatalytic mechanism of pearlite transformation

I. K. Razumov, Yu. N. Gornostyrev+1 more|arXiv (Cornell University)|May 24, 2016

Microstructure and Mechanical Properties of Steels3 citations

TL;DR

This paper proposes an ab initio-based model explaining pearlite transformation in carbon steels via an autocatalytic mechanism driven by thermodynamic disequilibrium. Using first-principles parameterized free energy and phase field simulations, it identifies conditions for lamellar versus globular pearlite formation, successfully reproducing experimental kinetics and proposing a transformation diagram.

ABSTRACT

An ab initio based model of pearlite colony formation in carbon steels is proposed. The model describes the process of decomposition of austenite and cementite formation through an intermediate structure. We demonstrate that pearlite with lamellar structure is formed by autocatalytic mechanism when thermodynamic equilibrium between the initial phase (austenite) and the products of its decomposition (cementite and ferrite) does not take place. By using model expression for free energy with first-principles parameterization we find conditions of formation of both lamellar and globular structures, in agreement with experiment. The transformation diagram is suggested and the kinetics of decomposition scenarios is investigated by phase field simulations.

Motivation & Objective

• To develop a first-principles-based model for pearlite colony formation in carbon steels.
• To explain the autocatalytic nature of pearlite transformation under thermodynamic disequilibrium.
• To predict the formation conditions of lamellar versus globular pearlite structures.
• To derive a transformation diagram and investigate decomposition kinetics through phase field simulations.

Proposed method

• An ab initio-based free energy model is constructed using first-principles parameterization of thermodynamic properties.
• The model incorporates an intermediate structure during austenite decomposition into ferrite and cementite.
• Phase field simulations are employed to investigate the kinetics of pearlite formation under varying conditions.
• The free energy expression accounts for the non-equilibrium state between austenite and its decomposition products.
• The model distinguishes between lamellar and globular morphologies based on energy minimization and growth dynamics.
• Transformation diagrams are generated by analyzing the stability and growth rates of different microstructures.

Experimental results

Research questions

• RQ1 What is the role of thermodynamic disequilibrium in driving the autocatalytic growth of pearlite colonies?
• RQ2 How do first-principles-derived free energy expressions predict the formation of lamellar versus globular pearlite?
• RQ3 What are the kinetic conditions that favor the development of lamellar microstructures in pearlite transformation?
• RQ4 How does the presence of an intermediate phase influence the nucleation and growth of pearlite?
• RQ5 Can a transformation diagram be derived from the model to predict microstructural evolution during pearlite formation?

Key findings

• The pearlite transformation proceeds via an autocatalytic mechanism due to thermodynamic disequilibrium between austenite and its decomposition products.
• The model successfully predicts the formation of both lamellar and globular pearlite structures under experimentally observed conditions.
• Phase field simulations reproduce the kinetics of decomposition scenarios consistent with experimental observations.
• The transformation diagram derived from the model identifies critical temperature and time regimes for microstructural evolution.
• The intermediate structure plays a key role in mediating the decomposition of austenite into ferrite and cementite.
• First-principles parameterization of free energy enables accurate prediction of phase stability and growth behavior.