Influence of strain induced melt activation (SIMA) on the morphology of primary phase in steel microstructure

Strain induced melt activation (SIMA) is the mechanism for the formation of the globular microstructure under the controlled working process followed by holding the specimen at a temperature between solidus & liquidus pertaining to the given alloy system. The effect of SIMA process on the microstructure of steel, 10% and 15% deformed at 900°C and holding at 1400°C for 3 and 5 min separately were investigated. The metallographic examination of the SIMA processed steel was done and compared with the as received steel. It was observed that SIMA processed steel shows the globular structure as compared with the unprocessed steel. It was also found that as the deformation percentage increases, more globular structure forms. Due to the globular microstructure, there is enhancement in the mechanical properties such as tensile strength and hardness. The parameter such as degree of warm working process, temperature and holding time are important factor in controlling SIMA process. During mechanical working in the SIMA process, strain energy gets stored in the material. The 15% deformation with 3 min holding time enhanced the hardness and ultimate tensile strength by approximately 8% respectively as compared with as received sample. This acts as a driving force for recrystallization of warm worked steel which resulted in equiaxed grains of primary phase in the microstructure.