| Multistage torsion tests in the temperature range of 850 to 1150℃ and over a strain rate range of 1.89×10^(-2) to 3.78×10^(-1)/sec were performed to study the static softening of V-microalloyed steel under isothermal conditions. The fractional softening FS decreased with reduction in temperature, T, pass, ε, and strain rate, ε˙. Due to the occurance of FS, the multistage curves fall below the peak of the continuous curve, but are above the steady state regime after the peak. The multistage flow stress envelope of pass 2 to 10 is flat because they become almost identical due to similar softening in the intervals. During the intervals of multistage schedules, the following microstructural changes take place : static recovery, static recrystallization and grain growth. Therefore, the multistage grain size, being a strong function of temperature and strain rate, is larger than that produced by dynamic recrystallization, and being still smaller than the original grain size. |
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