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

Abstract

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.