Yielding Behavior and Its Effect on Uniform Elongation of Fine Grained IF Steel

Interstitial free (IF) steel specimens with different mean grain sizes ranging from 0.4 to 12 mu m were fabricated by the accumulative roll bonding (ARE) process and subsequent annealing. Tensile tests at room temperature have revealed that by decreasing the mean grain size down to an ultra-fine range, the yielding behavior gradually changes from the continuous yielding to the discontinuous yielding, accompanying a yield drop phenomenon. It has been found that the yield stress of specimens having fine grain sizes shows extra-hardening, deviated from the original Hall-Petch relation for coarse-grained specimens in accordance with the discontinuous yielding. The Hall-Petch analysis also has indicated that the loss in the uniform elongation in the ultrafine grain size range is related to the appearance of the discontinuous yielding behavior.