Exploring the origin of variant selection through martensite-austenite reconstruction

ABSTRACT

An approach of near neighbour correlation, with manual intervention, was developed for reconstructing parent austenite microstructure in a martensitic stainless steel. This was validated in a ferrite-austenite dual structure. Two-hundred and twenty randomly selected austenite grains were reconstructed from the experimental EBSD (electron backscattered diffraction) measurements. From these reconstructions, martensite variant selection was quantified as the number of variants (n_V) and the variant selection index (VSI: a statistical index for the relative area fractions of the variants). For each prior austenite grain, both n_V and VSI appeared to depend on the associated transformation (austenite-martensite) strain. Selection of common variants between two neighbouring austenite grains was related to the presence of 60°<111 > or Σ3 boundary in the austenite phase and corresponding minimisation of the transformation strain.

KEYWORDS:

• Steel
• martensite
• reconstruction
• transformation strain
• variant selection
• EBSD

Acknowledgements

The authors would also like to express their appreciation for the usage of the National Facility of Texture and OIM (at IIT Bombay). Support from R&D management of M/s. Tata Steel ltd is also acknowledged.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was done as part of the PhD program which was supported by M/s Tata Steel Ltd, Jamshedpur.