The role of carbon segregation on nanocrystallisation of pearlitic steels processed by severe plastic deformation

TL;DR

This study investigates how carbon segregation influences nanocrystallisation in pearlitic steels subjected to severe plastic deformation, revealing carbon's role in grain boundary formation and nanostructure evolution.

Contribution

It provides new insights into the atomic-scale mechanisms of nanocrystallisation driven by carbon segregation during severe plastic deformation of steels.

Findings

Carbon segregates along dislocation and grain boundaries.

Nanoscale grain structures form with about 20 nm size.

Off-stoichiometry cementite diminishes with increasing shear strain.

Abstract

The nanostructure and the carbon distribution in a pearlitic steel processed by torsion under high pressure was investigated by three-dimensional atom probe. In the early stage of deformation (shear strain of 62), off-stoichiometry cementite was analysed close to interphase boundaries and a strong segregation of carbon atoms along dislocation cell boundaries was observed in the ferrite. At a shear strain of 300, only few nanoscaled off-stoichiometry cementite particles remain and a nanoscaled equiaxed grain structure with a grain size of about 20 nm was revealed. 3D-AP data clearly point out a strong segregation of carbon atoms along grain boundaries. The influence of this carbon atom segregation on the nanostructure formation is discussed and a scenario accounting for the nanocrystallisation during severe plastic deformation is proposed.