The strain dependence of postdynamic recrystallization in 304 H stainless steel

Using double-hit hot compression tests, the softening behavior of 304 H stainless steel was studied during unloading. The prestrains used were associated with the initiation of dynamic recrystallization (DRX) (ε _c), the peak strain (ε _p), 1/2 (ε _c+ε _p), the strain at maximum softening rate (ε _i), and the onset of steady state flow (ε _s). The following conditions of deformation were used: T=1000 °C, 1050 °C, and 1100 °C, =0.01 and 0.1 s⁻¹, and delay times of 0.3 to 1000 seconds. To define the above important strains, single-hit hot compression tests were performed over a wider range of deformation conditions than the double-hit ones—i.e., 900 °C to 1100 °C and =0.01 to 1 s⁻¹. The results show that a transition strain (ε*) separates the strain-dependent range of postdynamic softening from the strain-independent range. At strains between ε _c and ε*, both metadynamic and static recrystallization contribute to interhit softening. The value of ε* obtained in this work was ε*=4/3 ε _p. It was also found that the strain hardening rate was identical at all the critical strains (ε*) and took the value −22 MPa.