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

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.

Keywords:

• Carbon
• ordering
• spinodal decomposition
• defects
• segregation

Acknowledgements

The authors would like to thank the Diamond Light Source for access to Beamline I11 and the beamline team for the measurements under Rapid Access mode. Author BK would like to express her gratitude to Mr Hans Hofman for his help in carrying out the heat treatments. The authors would like to thank the National Atom Probe Facility at TU Eindhoven, particularly Dr Sebastian Koelling for the sample preparation and measurements on the LEAP.

Notes

No potential conflict of interest was reported by the authors.

Additional information

Funding

The research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Programme FP7/2007-2013 / ERC [grant agreement number 306292].