Crystallographic variant selection of martensite during fatigue deformation

Abstract

Metastable austenitic stainless steels are prone to form deformation-induced martensite under the influence of externally applied stress. Crystallographic variant selection during martensitic transformation of metastable austenite has been investigated thoroughly with respect to the interaction between the applied uniaxial cyclic stress and the resulting accumulated plastic strain during cyclic plastic deformation. The orientation of all the Kurdjomov–Sachs (K-S) variants has been evaluated extensively and compared with the measured orientation of martensite with their corresponding interaction energies by applying the elegant transformation texture model recently developed by Kundu and Bhadeshia. Encouraging correlation between model prediction and experimental data generation for martensite pole figures at many deformed austenite grains has been observed. It has been found that both the applied uniaxial cyclic stress and the accumulated plastic strain are having strong influence on crystallographic variant selection during cyclic plastic deformation. Patel and Cohen’s classical theory can be utilized to predict the crystallographic variant selection, if it is correctly used along with the phenomenological theory of martensite crystallography.

Keywords:

• stress-induced martensite
• strain-induced martensite
• variant selection
• interaction energy
• austenitic stainless steels
• low cycle fatigue

Acknowledgements

I am grateful to the Ministry of Science & Technology, Department of Science & Technology, Government of India for the BOYSCAST Fellowship. I express my sincere gratitude to Dr S. Tarafder, Chief Scientist of CSIR-National Metallurgical Laboratory, Jamshedpur, Professor P. C. Chakraborti, Department of Metallurgical and Material Engineering, Jadavpur University, Kolkata for their fruitful suggestions and discussions. Dr S. Kundu, Head, Product Research Group, Tata Steel, Jamshedpur is also gratefully acknowledged for his help in programming and discussions. I am also grateful to Professor H. K. D. H. Bhadeshia for suggestions, stimulating discussions and the provision of laboratory facilities at the Phase Transformation & Complex Properties Research Group, Department of Materials Science and Metallurgy, University of Cambridge, UK during the fellowship (2009–2010). I would also like to thank all the respected reviewers for their positive and constructive recommendations which helped a lot to prepare this revised manuscript.