Effect of deformation condition on structure development in nickel base alloy

This research provides an attempt to achieve uniform grain structure by recrystallization process in NiMoCr alloy after different hot- and cold-working application. The changes in microstructure resulting from thermomechanical processing were investigated by optical microscopy. The results showed that homogeneity of the recrystallized structure is strongly related to the amount of sample reduction imposed during hot working and to the period of annealing time. Furthermore, the results illustrate that the recrystallized structure at the surface was finer, than in the interior of the sample. This is due the specimen surface, which is more strain exposed for applied deformation and driving force for primary recrystalization in sample surface area is therefore higher than in central part of samples. Then, using conventional two-step hot rolling, the expected uniform recrystallized microstructure could not be obtained across the width of slab. An unfavourable contribution at recrystalization process was observed from initial grain size heterogeneity of as-cast ingot structure. However, after additional introduction of cold rolling, which followed hot working the more uniform recrystallized grain structure was achieved after recrystallization annealing.