  Plastic flow behavior of low carbon steel has been studied at room
temperature during tensile deformation by varying the initial strain rate of
3.3x10e-4 1/sec to the final strain rate ranging from 1.33x10e-3 1/sec to
2.0x10e-3 1/sec at a fixed engineering strain of 12%. Haasen plot revealed that
the mobile dislocation density remained almost invariant at the juncture where
there was a sudden increase in stress with the change in strain rate and the
plastic flow was solely dependent on the velocity of mobile dislocations. In
that critical regime, the variation of stress with time was fitted with a
Boltzman type Sigmoid function. The increase in stress was found to increase
with final strain rate and the time elapsed to attain these stress values
showed a decreasing trend. Both of these parameters saturated asymptotically at
higher final strain rate.
