Autocatalytic mechanism of pearlite transformation in steel

TL;DR

This paper presents a model for pearlite formation in steel, highlighting an autocatalytic mechanism influenced by magnetic order and thermodynamic conditions, validated through phase field simulations and experimental agreement.

Contribution

It introduces a first-principles parameterized model explaining the autocatalytic pearlite formation process in steel.

Findings

Pearlite forms via an autocatalytic mechanism under certain conditions.

The model predicts both lamellar and globular structures consistent with experiments.

Transformation diagrams and kinetic scenarios are explored through simulations.

Abstract

A model of pearlite colony formation in carbon steels with ab-initio parameterization is proposed. The model describes the process of decomposition of austenite and cementite formation through a metastable intermediate structure by taking into account the increase of the magnetic order under the cooling. Autocatalytic mechanism of pearlite colony formation and the conditions for its implementation have been analyzed. 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 different scenarios in the kinetics of decomposition are investigated by phase field simulations.