Thermodynamic aspects of carbon redistribution during ageing and tempering of Fe–Ni–C alloys

B Kim,J Sietsma,M J Santofimia

doi:10.1080/14786435.2016.1211790

B Kim, J Sietsma + Show 1 more

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https://doi.org/10.1080/14786435.2016.1211790

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Journal: Philosophical Magazine	Publication Date: Jul 26, 2016
Citations: 13	License type: open-access

Affiliation: Delft University of Technology

Abstract

Carbon redistribution is known to occur during martensite ageing. The two associated processes most discussed in the literature are spinodal decomposition and carbon segregation to defects. In order to elucidate the topic, the ageing and tempering of two Fe–Ni–C alloys have been characterised by means of atom probe tomography and synchrotron radiation diffraction. Upon ageing at room temperature, carbon redistribution is clearly observed, where the process of carbon segregation to defects appears to be most likely to occur. Nevertheless, the possibility of spinodal decomposition is not entirely discarded, and the current work presents a series of discussion points that challenge our current understanding of the thermodynamic of ferrite in steels.

Highlights

Understanding carbon redistribution in steels poses a challenge, especially in complex microstructures, where there are numerous microstructural features that can affect carbon behaviour
Earlier electron microscopy studies on aged martensite led some researchers to conclude that the origin of these local variations was spinodal decomposition [1,2], while others have interpreted the observations as carbon segregating to defects within the microstructure [3,4]
Two competitive mechanisms for carbon redistribution during room temperature martensite ageing have been reviewed in the context of spinodal decomposition vs. carbon segregation to defects

Summary

Introduction

Understanding carbon redistribution in steels poses a challenge, especially in complex microstructures, where there are numerous microstructural features that can affect carbon behaviour. Earlier electron microscopy studies on aged martensite led some researchers to conclude that the origin of these local variations was spinodal decomposition [1,2], while others have interpreted the observations as carbon segregating to defects within the microstructure [3,4]. Whether these two mechanisms of carbon redistribution take place simultaneously and interact, or one occurs predominantly, is still not understood [5]

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