| The transition from single- to multiple-peak dynamic recrystallization flow curves of V-microalloyed steel was studied by torsion test in the temperature range of 900℃ to 1000℃ and over a strain rate range of 2.0×10^(-2) to 1.0×10^0//sec. The grain size of the dynamically recrystallized specimens decreased with increasing Zener-Holloman parameter, Z without exhibiting any dependence on the initial grain size. The real transition occurred at the upper Z values, 2.0×10^(11)∼2.0×10^(10) than that determined by ε_x = ε_p. On the initial grain size D_0, dependence of the critical condition for the flow curve transition, Z_c, the equivalency with Z vs. D, relation was not observed. Therefore, the criterion D_o=2D_s has an applicability for only a limited range of Z. The constitutive equation of D, vs. Z could be described by D_s =897.865 Z^(-1.04)(㎛) |
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