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 12μm were fabricated by the accumulative roll bonding (ARB) 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 HallPetch relation for coarse-grained specimens in accordance with the discontinuous yielding. The HallPetch 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.