Dynamic recrystallization (DRX) behavior of AISI 422 martensitic stainless steel has been investigated at deformation temperatures of 950-1150 ºC and strain rates of 0.01-1 s -1 . The critical stress for initiation of DRX was determined based on strain hardening rate dependence to flow stress. The normalized critical stress was estimated as σ c /σ P =0.84. In addition, considering the material constants as a function of strain via a third order polynomial fitting, the effect of strain was investigated using an Arrhenius type constitutive equation. Furthermore, in order to examine the competency of the strain-dependent constitutive equations to predict flow stress curves of AISI 422 martensitic stainless steel, two of these constitutive models (Akbari and Ebrahimi models) were investigated. It was found that Akbari et al. constitutive equation cangive a more precise estimation of flow stress curves for the alloy of this study.

The metadynamic softening behavior and grain size refinement of an AISI 422 martensitic stainless steel in the temperature range of 950-1150 ºC was investigated by double-hit compression tests. The deformed specimens were held at deformation temperature with delay times of 5 to300s after achieving a strain of 0.3. The results indicated that at deformation temperatures lower than 1050 ºC, the final average grain size decreases with increasing time, attaining a minimum value at 15s,. However, grain coarsening was observed at deformation temperatures of 1150 and 1100 ºC. Based on the experimental results, a model was established for estimation of the softening fraction at different deformation parameters. The finer grain size was achieved by prior fine pre-austenite grain and lower secondary deformation temperature. The initial grain size of ASTM 5.5 decreased down toASTM7 to ASTM 8.5 at the deformation temperatures of 1020 ºC and 940 ºC, respectively. More uniform grain distribution was obtained with decreasing initial grain size especially at lower deformation temperatures.