In order to produce new high Mn-high C austenitic steels (R m> 700 MPa) , different tests and methods were used to determine a suitable window of process parameters. In-situ melting hot tensile tests and hot compression tests were carried out to investigate the hot ductility, fracture characteristics and flow behaviour during continuous casting and hot deformation of 3 steels with Mn and C contents between 9-23% and 0.6-0.9%, respectively. The results show that these steels are susceptible to interdendritic fracture at high temperatures. Decreas ing Mn content improves the reduction of area at high temperatures to 60% or more. Hot deformation loads for process ing the investigated steels are not higher in comparison to the stainless steel 1.4301.

Microalloying elements like Al, B, Nb, Ti ,V can be used to optimise the microstructure evolution and the mechanical properties of advanced high strength steels (AHSS). Microalloying elements are characterised by small additions < 0.1 mass% and their ability to form carbides or nitrides. They can increase strength by grain refinement and precipitation hardening, retard or accelerate transformations and affect the diffusion kinetics as well as the stacking fault energy. Thus, by their addition the AHSS with their high requirements to process control can be adopted to existing processing lines. Different combinations of microstructural phases and different chemical compositions have been investigated for AHSS in order to combine high strength with excellent formability. The recently developed high manganese steels further improve the formability due to their austenitic microstructure and inherent phase transformations during forming.

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Tensile properties of high Mn austenitic Fe‐26.5Mn‐3.6Al‐2.2Si‐0.38C‐0.005B (HM1) and Fe‐18.9Mn‐0.62C‐0.02Ti‐0.005B (HM2, in mass%) steels after different solution treatments have been investigated. The results show that the solution treatment has a significant influence on microstructure and mechanical properties of the investigated steels. By appropriate solution treatment the product of tensile strength (Rm) and total elongation (A50) of the hot rolled steel can be improved from ˜ 40000‐50000 MPa% to ˜ 55000‐65000 MPa% depending on the steel chemical composition. A solution treatment with a very high temperature, e.g. at 1100 °C for the Fe‐18.9Mn‐0.62C‐0.02Ti‐0.005B steel, results in a significant increase in the ϵ‐martensite fraction during quenching. This deteriorates the ductility of the steel. A solution treatment at low temperature in the austenitic range, e.g. at 700 °C for the Fe‐18.9Mn‐0.62C‐0.02Ti‐0.005B steel, results in a decrease in the grain size of the steel. This suppresses the ϵ‐martensite transformation during cooling. EBSD measurements revealed the mechanisms contributing to the overall plasticity of the investigated steels on the microscale. The plasticity of the 26.5Mn‐3.6Al‐2.2Si‐0.38C‐0.005B steel is produced mainly by TWIP mechanism under the examined experimental conditions, whereas for the Fe‐18.9Mn‐0.62C‐0.02Ti‐0.005B steel TWIP and TRIP mechanisms occur with different degrees depending on the test temperature of the tensile test.

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