Pearlite in Multicomponent Steels: Phenomenological Steady-State Modeling

Jia-Yi Yan,John Ågren,Johan Jeppsson

doi:10.1007/s11661-020-05679-3

Abstract

A steady-state model for austenite-to-pearlite transformation in multicomponent steel is presented, including Fe, C, and eight more elements. The model considers not only classic ingredients (formation of ferrite–cementite interface, volume diffusion, boundary diffusion, and optimization of lamellar spacing) but also finite austenite–pearlite interfacial mobility that resolves some previous difficulties. A non-Arrhenius behavior of interfacial mobility is revealed from growth rate and lamellar spacing data. A smooth and physical transition between orthopearlite and parapearlite is realized by optimizing the partitioning of substitutional alloying elements between ferrite and cementite to maximize growth rate or dissipation rate while keeping carbon at equilibrium. Solute drag effect is included, which accounts for the bay in growth rate curves. Grain boundary nucleation rate is modeled as a function of chemical composition, driving force, and temperature, with consideration of grain boundary equilibrium segregation. Overall transformation kinetics is obtained from growth rate and grain boundary nucleation rate, assuming pearlite colonies only nucleate on austenite grain boundaries. Further theoretical and experimental work are suggested for generalization and improvements.

Highlights

PEARLITE is a common product of austenite decomposition in steels, typically consisting of alternating lamellae of ferrite and cementite
There has been a compilation of information on the morphology, growth rate, lamellar spacing, partitioning of alloying elements, nucleation, and overall transformation kinetics of pearlite formation
For multiple solute drag elements, their solute drag forces are assumed to be additive. We find it sufficient to use a simple model for the solute drag effect on steady-state growth rate of pearlite

Summary

Introduction

PEARLITE is a common product of austenite decomposition in steels, typically consisting of alternating lamellae of ferrite and cementite. It is known as a product combining good strength and ductility obtained from relatively simple heat treatment of carbon or low-alloy steels. Pearlitic steels are widely used for steel wire and rail.[1] It is of great practical interest to accurately model the overall transformation kinetics of austenite decomposition to pearlite. Quantitative experimental characterizations of pearlite date back to the 1930s.[2] Since there has been a compilation of information on the morphology, growth rate, lamellar spacing, partitioning of alloying elements, nucleation, and overall transformation kinetics of pearlite formation (see References 3 through 6 for example).

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Discussion

Conclusion