Grain growth behaviour of an AISI 422 martensitic stainless steel after hot deformation process

The metadynamic softening behaviour and grain size refinement of an AISI 422 martensitic stainless steel in the temperature range of 950-1150 degrees C was investigated by double-hit compression tests. The deformed specimens were held at deformation temperature with delay times of 5-300s after achieving a strain of 0.3. Based on the experimental results, a model was established for estimation of a softening fraction at different deformation parameters, and the softening fraction was compared with a recrystallised fraction. A major deviation was observed at the beginning of interpass time denoting a significant contribution of recovery to the fractional softening (FS). However, by increasing the time and temperature, the difference between the FS and recrystallised fraction is reduced. The finer grain size was achieved by prior fine pre-austenite grain and lower secondary deformation temperature. The initial grain size of 53 mu m decreased down to 32 and 19 mu m at the deformation temperatures of 1020 and 940 degrees C, respectively. The austenite grains have considerable growth at a temperature higher than 1020 degrees C, while the grain coarsening is negligible at lower deformation temperatures.