X-ray diffraction and Mössbauer spectroscopy studies of cementite dissolution in cold-drawn pearlitic steel

Abstract

Cementite dissolution in cold-drawn pearlitic steel (0.8 wt.% carbon) wires has been studied by quantitative X-ray diffraction (XRD) and Mössbauer spectroscopy up to drawing strain 1.4. Quantification of cementite-phase fraction by Rietveld analysis has confirmed more than 50% dissolution of cementite phase at drawing strain 1.4. It is found that the lattice parameter of the ferrite phase determined by Rietveld refinement procedure remains nearly unchanged even after cementite dissolution. This confirms that the carbon atoms released after cementite dissolution do not dissolve in the ferrite lattice as Fe-C interstitial solid solution. Detailed analysis of broadening of XRD line profiles for the ferrite phase shows high density of dislocations (∼10¹⁵/m²) in the ferrite matrix at drawing strain 1.4. The results suggest a dominant role of ⟨1 1 1⟩ screw dislocations in the cementite dissolution process. Post-deformation heat treatment leads to partial annihilation of dislocations and restoration of cementite phase. Based on these experimental observations, further supplemented by TEM studies, we have suggested an alternative thermodynamic mechanism of the dissolution process.

Keywords:

• pearlitic steel
• cementite dissolution
• X-ray diffraction
• Mössbauer spectroscopy
• transmission electron microscopy

Acknowledgements

TATA steel is gratefully acknowledged for the full financial support in the present work. The authors would like to thank the Director, NML for his constant inspiration and support to carry out the present investigation.