In situ TEM observations of the growth of bainitic ferrite in an Fe-0.3C-3Mn-1.5Si-0.15Mo steel

Abstract

The current study reports in situ TEM observations of the growth of bainitic ferrite in an Fe-0.3C-3Mn-1.5Si-0.15Mo steel held isothermally at 300 °C with a higher spatio-temporal resolution than in previous studies. Significant variations were found in the lengthening rate, with the highest being in excess of 30,000 nm.s−1 while more common lengthening rates of 10–1000 nm.s−1 provided the highest quality observations. Both sheaves with visible sub units and individual laths were observed during growth with the lengthening behaviour of sheaves found to be discontinuous - in the most favourably oriented sheave this could be linked to sub unit behaviour. The transformation behaviour was comparable to that of HT-LSCM observations of bainitic ferrite growth for the most comparable steel compositions and to ‘textbook’ descriptions of the formation of bainite sheaves. In addition, other relevant phenomena were recorded, including the generation and movement of dislocations in the austenite during transformation, the interaction of laths with twin boundaries and the initially slow growth of bainitic ferrite laths.