An investigation on full annealing temperature and annealing twins’ Density in Fe-33Mn-3Si-2Al high-manganese steel

Twinning induced plasticity (TWIP) steels with high manganese percentage (17-35%), are mostly used in automotive bodies. Their microstructure at room temperature is austenitic, and due to the low stacking fault energy, major deformation mechanism in them is twinning inside austenite grains which leads to enhanced mechanical strength in the steel. Due to the important effect of heat treatment process on mechanical properties, full annealing heat treatment and resultant twins were investigated in this study. To this aim, the steel was casted, hot rolled, and then heat treated at different times and temperatures and the obtained microstructures were analyzed using optical microscope. The results showed that the percentage of annealing twins is increased with increasing annealing temperature up to 1100 °C, the peak point at which grain growth stage starts, and increasing temperature above that decreases twins’ percentage. A relation between grain size and annealing twins’ percentage was found. Full annealing temperature for this steel was determined to be 1100 °C.