Effect of prior austenite grain size on the formation of carbide-free bainite in low-alloy steel

ABSTRACT

Inconsistencies exist in literature regarding the effect of prior austenite grain size (PAGS) on the extent and kinetics of bainite transformation. Attempts have been made in the present work to address these issues in a low-alloy carbide-free bainitic steel using dilatometry, over a range of PAGS. The bainite transformation kinetics in the above-mentioned conditions have been analysed quantitatively using established kinetic model to extract information related to the transformation mechanisms in such conditions. Greater obstruction from grain boundaries in fine-grained austenite restricts sheaves of bainite to develop completely and thereby reduces the volume fraction of bainite in comparison with coarse-grained austenite. Initial nucleation rate of bainite transformation increases with decreasing PAGS due to an increase in the nucleation site density. However, the maximum nucleation rate decreases consistently with decreasing PAGS due to gradual reduction in the autocatalytic factor.

KEYWORDS:

• Carbide-free bainite
• prior austenite grain size
• dilatometry
• transformation kinetics
• microstructure

Acknowledgements

The authors gratefully acknowledge the financial support from Indian Institute of Technology Kharagpur. Authors are thankful to all the staff members of Steel Technology Centre and Central Research Facility for providing various research facilities and assistance.

Disclosure statement

No potential conflict of interest was reported by the author(s).