Therefore, according to
Equation 2,
the onsets of DT and DRX are associated with inflection points in
a θ − σ plot and with minima in a −(∂θ/∂σ) versus σ curve. In most
cases, there are two inflection points, the first of which indicates the
onset of DT and the second is the initiation of DRX.
The −(∂θ/∂σ) versus σ curves for the first hit and second hit for
medium-carbon low-alloy steel at various experimental temperatures and
strain rates are shown in Figs.
3
a and 3 b, respectively. The two minima displayed in Figs. 3 represent
the critical stresses at which DT were initiated during deformation. The
graph in Fig. 4 show the dependence of DT critical stress versus
temperature and strain rate. It can be seen that with the increase in
temperature the critical stresses for DT decreases in both first and
second hit deformation, whereas, the critical stress for DT increases
with strain rate for both first and second hit deformation.