5th International High Manganese Steel Conference - HMNS 2022

Medium manganese sheet steels show an excellent combination of strength and ductility. Typically, they have a duplex type microstructure consisting of ferrite and austenite layers after cold rolling and subsequent intercritical annealing. The thermomechanical rolling produces a mixture of bainite, martensite and retained austenite instead of typical duplex microstructures. Their forming behaviour is not fully understood especially for thermomechanically processed conditions. Therefore, the present work aims at comparing the dynamic mechanical behaviour and microstructure of two medium manganese sheet steels (3Mn-Al and 5Mn-Al) alloyed with aluminum addition. The static tensile tests and rotary hammer tests at strain rates of 250, 500 and 1000 s-1 were applied. Mechanical properties under dynamic tensile loads were determined, which are significantly affected by a manganese content in a range from 3 to 5%. In both steels the tensile strength increased with increasing strain rate but the applied strain rate range had a moderate effect on the mechanical behavior. The higher strength properties showed the 5Mn-Al steel with a tensile strength level higher than 1200 MPa. On the other hand, the 3Mn-Al steel was characterized by better ductility due to a larger retained austenite amount and more enhanced TRIP effect. The mechanical properties of low-Mn steel were more strain-rate sensitive compared to the static mechanical behavior. The microstructure features and phase composition were assessed in detail using XRD and SEM tests. The morphology of structural constituents and quantification of microstructural details were done using advanced EBSD studies.