Predicting the Transition between Upper and Lower Bainite via a Gibbs Energy Balance Approach

Journal article (2016)

Authors

W. Xu Novel Aerospace Materials - Aerospace Engineering , Northeastern University China
Zhigang Yang Tsinghua University
Chi Zhang Tsinghua University
H. Chen Tsinghua University, Novel Aerospace Materials - Aerospace Engineering
S. van der Zwaag Novel Aerospace Materials - Aerospace Engineering
Research Group
Novel Aerospace Materials (Aerospace Engineering) (TU Delft)
Low-alloy steel Bainite Gibbs energy balance Interface migration Carbon diffusion
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Published Date

2016

Language

English

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Faculty

Aerospace Engineering

Department

Aerospace Structures & Materials

Research Group

Novel Aerospace Materials

Abstract

The transition temperature between upper bainite and lower bainite is calculated with an extended Gibbs energy balance model, which is able to quantitatively describe the evolution of carbon supersaturation within bainitic ferrite sheaves during the entire thickening process. The nucleation rate of intra-lath cementite precipitation on a dislocation is calculated based on of the degree of carbon supersaturation. Upper bainite and lower bainite are thus distinguished by the effective nucleation density and therefore a numerical criterion can be set to define the transition. The model is applied to Fe-xC-1Mn/2Mn/1Mo ternary alloys. Results show that the transition temperature increases with bulk carbon content at lower carbon concentration but decreases in the higher carbon region. This prediction agrees very well with the experimental observations in Mn and Mo alloyed systems. Moreover, the highest transition temperature and the carbon content at which it occurs in the Fe-xC-2Mn system are in good agreement with reported experimental data. The inverse V shaped character of the carbon concentration-transition temperature curve indicates two opposite physical mechanisms operating at the same time. An analysis is carried out to provide an explanation.