Ferrite grain size refinement by heavy deformation during accelerated cooling in low-carbon steel

It is well established that the ferrite grain size of low-carbon steel can be refined by hot rolling of the austenite at temperature below the-nonrecrystallization temperature (T-nr). The strain retained in the austenite increases the number of ferrite nuclei, In present study a C-Mn steel is heavily deformed by compression at temperature below the determined T-nr for this steel during accelerated cooling. Compression experiments are carried cut at various cooling rates before deformation and temperatures. The ferrite grain size and the ferrite/bainite phase fraction are extensively examined. It is observed that heavy deformation during accelerated cooling widens the range of transformation temperature of austenite to ferrite. If cooling rate before deformation is set to be high (similar to 50 Ws) and deformation temperature decreases down to 530 degrees C, the attainable fraction of ferrite increases instead of decrease of bainite. Ferrite could be a predominate phase transformed from severely deformed austenite at significantly low temperature (dawn to 530 degrees C), in which, unless deformed bainite commonly forms from austenite. Enabling the transformation to ferrite at very low temperature leads to a progressive reduction of the ferrite grain size down to 1 mu m. possible mechanism of the strain assisted low temperature transformation to ferrite is discussed.