the effect of carbon content of the mechanical properties - McMaster ...

M.A.Sc. Thesis – E. E. Yang McMaster – Materials Science & Engineering
5.2.2. Work Hardening Response
The work hardening response was examined by taking the derivative of the plastic
flow curve (dσt/dεt) vs. σt, to examine the rate at which the material work hardened. The
onset of plastic instability by the Considère’s criterion was used to determine the value of
uniform elongation for each alloy. This was computed by overlaying a dσ/dε = σt line
along with the work hardening curve to determine the stress at the intersection. The
serrations seen in the upper region of the monotonic tensile curve for the 0.6C and 0.4 C
alloys led to large fluctuations in the derivatives and these were filtered using a 5 point
averaging scheme to decrease the fluctuations. The resulting work hardening curves are
seen in Figure 5.8, where the serrations for the 0.6C and 0.4C alloy can be seen to be
significant despite the use of the filter.
The 0.6C and 0.4C alloy work hardening rates decreased rapidly during initial
deformation and after a strain of ~0.10, the work hardening rate started to increase, as a
result of the onset of twinning. The 0.6C alloy exhibited a larger uniform elongation than
the 0.4C alloy, with a larger region of high work hardening rate values before fracture.
The consistently higher work hardening values observed is commonly seen for TWIP
alloys (Bouaziz 2009). The dual-phase 0.2C alloy showed a higher initial work hardening
rate versus the 0.6C and 0.4C alloys and displayed a slight increase with plastic
deformation before becoming relatively constant, prior to decreasing to failure. The
exhibited behaviour was characteristic of a TRIP alloy for the 0.2C alloy (Liang 2008).
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