Abstract
The scientific aim of the paper is the comparative analysis of the hot-working behaviour and microstructure evolution of thermomechanically processed and controlled cooled three advanced high-strength steels (AHSS) used in the automotive industry. The hot workability of three selected steel grades with a various content of Mn and C being major austenite-forming elements was compared. Evaluation of the resistance for hot deformation was carried out on a basis of continuous compression, double-hit compression, four-step compression and seven-step compression experiments simulating conditions similar to industrial processes. It was found that the hot workability of the new generation of AHSS is very challenging due to high values of flow stresses required. However, it is possible to obtain fine-grained transformation products of supercooled austenite with a high volume fraction of retained austenite for low-alloyed steels or single-phase austenitic microstructure in the high-manganese steel. Thermally activated processes of microstructure restoration which enable for successive grain refinement and affecting final flow stress values were identified. Finally, the comparison of the microstructures characterizing the first, second and third generation of AHSS was carried out. Some similarities and differences concerning the hot deformation behaviour and microstructure detailes are indicated.