Carbon Ordering in Martensite Lattice Under External Stress: Thermodynamic Theory and Molecular Dynamics Simulation

Abstract

Rapid cooling of the Fe–C fcc solution leads to the formation of a phase called martensite, which has high mechanical properties. It is well known that under stress a martensite has the ability to plastically deform within a small range, despite the large value of the macroscopic yield strength. This effect is explained in different ways, mainly on the basis of dislocation theory. We study the impact of external stress on ordering of interstitial atoms in Fe–C solid solutions and formation of tetrahedral distortion of martensite lattice. Molecular dynamics with embedded atom (EAM) interatomic potential is used. According to the simulations, interstitial carbon atoms migrate under external stress applied along the tetragonality direction from z‐sublattice, and tetrahedral distortion of lattice changes its orientation to other ones when the stress exceeds some critical value. This result enables us to justify a new look at the nature of the martensite plastic deformation. The influence of temperature and carbon content on the critical stress value is investigated.