STRUCTURE AND MECHANICAL PROPERTIES OF HIGH-Mn TWIP STEEL AFTER THEIR THERMO-MECHANICAL AND HEAT TREATMENTS

The aim of this paper is to determine the impact of heat treatment of steel pre-treated thermo-mechanically using Gleeble 3800 simulator on the structure and mechanical properties of investigated high-manganese austenite Fe-Mn-(Al, Si) steel, containing 25% of Mn, 3% of Si, and 3% of Al. Applying thermo-mechanical treatment using Gleeble 3800 simulator allow to obtain the conditions for a gradual grain refinement controlled mainly by dynamic recrystallization and also by a dynamic recovery in a whole temperature deformation range. The high-manganese TWIP steel after hot-deformation is characterized by a mixture of fine, recrystallized grains and some fraction of dynamically recovered grains with a mean diameter of about 5-7 mu m. Solution heat treatment of the specimens from a temperature 850 mu C cause that steel possesses fine-grained microstructure of austenite with grain sizes about 10 mu m. Increasing solution temperature from 850 to 1000 degrees C results in a rapid grain growth up to about 17 mu m. Specimens were annealing at time 900 s, increasing solution time also cause a growth of austenite mean grain size in high-manganese Fe-25Mn-3Si-3Al TWIP steel. The new developed high-manganese TWIP steels provide an extensive potential for automotive industries through exhibiting the twinning induced plasticity (TWIP) and transformation induced plasticity (TRIP) mechanisms. TWIP steels not only show excellent strength, but also have excellent formability due to twinning, thereby leading to unique combination of strength, ductility, and formability over conventional dual phase steels or transformation induced plasticity TRIP steels.