Quantum-mechanical analysis of effect of alloying elements on \u03b5-martensite start temperature of steels

J H Jang,T-H Lee,J Moon,D-W Suh,H-Y Ha

doi:10.1038/s41598-017-18230-z

J H Jang, T-H Lee + Show 3 more

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https://doi.org/10.1038/s41598-017-18230-z

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Journal: Scientific Reports	Publication Date: Dec 1, 2017
Citations: 7	License type: open-access

Affiliation: Korea Institute of Materials Science

Abstract

With regard to the transformation mechanism of austenitic high manganese steel, the prediction of the ε-martensite start temperature is a critical consideration in alloy design. Evaluation of the ε-martensite start temperature makes it possible to predict the microstructure and to understand the phase transformation occurring during deformation. Here we use the quantum mechanical calculation of random alloys to understand the physics for ε-martensitic transformation in steels. We could find the linear relationship between the measured ε-martensite start temperatures and the crystal structure stability for various compositions. We also could estimate the effect of several alloying elements. It is expected that the effect of decreasing the temperatures for the same amount of alloying elements addition will be larger moving farther from Group VIII. By creating a free-energy model that reflects the temperature effect, we were able to calculate the average driving force required for the ε-martensitic transformations.

Highlights

Martensitic transformation in steels is an important phenomenon that affects their mechanical properties and has been studied extensively
The martensitic transformation is a process that changes a crystal structure by a homogeneous deformation without any change in composition. This transformation is initiated when the difference in free energy between two crystal structures exceeds a certain critical value, which is determined by stored energy or kinetic phenomena
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Summary

Introduction

Martensitic transformation in steels is an important phenomenon that affects their mechanical properties and has been studied extensively. Austenitic steels including high Mn steels, light-weight steels, austenitic stainless steels, and shape-memory alloys have been studied extensively[7,8,9] In those alloys, a change from austenite to ε-martensite with a hexagonal close packed (HCP) structure rather than α′-martensite may be observed during cooling[9]. It is generally accepted that the ordinary deformation mechanism of austenitic steel is mainly determined by the stacking fault energy (SFE), and that the main factor determining SFE is the relative lattice stabilities of the FCC and HCP structures, as in the ε-martensitic transformation[10]. First-principles studies on the effect of elements on the lattice stability or SFE are ongoing, the compositional range of the alloys remain limited[14,15,16]

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