Annealing behavior of severely deformed IF steel via the differential speed rolling method

The present study was made to demonstrate the annealing behavior of severely deformed interstitial free (IF) steel processed by differential speed rolling (DSR). The initial ferrite grain size of ≈35 μm was significantly refined to ≈0.7 μm after four DSR operations corresponding to the effective strain of ≈1.7 under the roll speed ratio of 1:4 for lower and upper rolls. Microstructural observations revealed that most of the initial coarse ferrite grains were subdivided with an aid of dislocation activities, resulting in the formation of fine ferrite grains. During post-DSR annealing at 673–773 K, the grain size of the fine ferrite grains was observed to remain unchanged, which implied that static recovery was in progress. At 823 K, the microstructure exhibited the coarse recrystallized ferrite grains while the grain growth of ferrite grains started to take place above 873 K. Mechanical properties were also assessed by taking the annealing characteristics of the ultrafine grained IF steel into consideration.