Towards the ab initio based theory of the phase transformations in iron and steel

TL;DR

This paper reviews recent progress in developing an ab initio based quantitative theory for phase transformations in steel, linking magnetic order and microstructure evolution during cooling.

Contribution

It introduces a novel ab initio parameterization of the Ginzburg-Landau functional to model steel phase transformations and microstructure formation.

Findings

Transformation scenarios change with cooling from ferrite to martensite.

Short-range magnetic order influences transformation pathways.

Phase-field modeling captures typical transformation patterns.

Abstract

Despite of the appearance of numerous new materials, the iron based alloys and steels continue to play an essential role in modern technology. The properties of a steel are determined by its structural state (ferrite, cementite, pearlite, bainite, martensite, and their combination) that is formed under thermal treatment as a result of the shear lattice reconstruction "gamma" (fcc) -> "alpha" (bcc) and carbon diffusion redistribution. We present a review on a recent progress in the development of a quantitative theory of the phase transformations and microstructure formation in steel that is based on an ab initio parameterization of the Ginzburg-Landau free energy functional. The results of computer modeling describe the regular change of transformation scenario under cooling from ferritic (nucleation and diffusion-controlled growth of the "alpha" phase to martensitic (the shear lattice instability "gamma" -> "alpha"). It has been shown that the increase in short-range magnetic order with decreasing the temperature plays a key role in the change of transformation scenarios. Phase-field modeling in the framework of a discussed approach demonstrates the typical transformation patterns.