The Effect of Hot Deformation Parameters on Grain Size Refinement in a Martensitic Stainless Steel

The grain size refinement of AISI 422 martensitic stainless steel in the temperature range of 950-1150 ºC was investigated by hot deformation tests. The deformed specimens were held at deformation temperature with delay times of 5 to 300s after achieving a strain of 0.3. The austenite grains exhibit a considerable growth at temperature higher than 1050˚C, while the grain coarsening is negligible at lower deformation temperatures. Therefore, it is a difficult task to achieve a fine grain structure at these high deformation temperatures. In the second stage of this work, the grain growth behavior of the deformed alloy at temperature range of 940-1020 ºC was investigated to obtain a fine austenite grain in the final deformation step. A uniform and fine-grain structure, with average grain size less than 30 µm, can be obtained by considering the appropriate temperature and strain per pass. At 1020˚C a relatively fine and uniform recrystallized grain, mean grain size of about 28 µm, is obtained with an applied strain of 0.4, while at 980˚C after strain of 0.2 a nearly equiaxed grain with the same mean grain size is achieved.