Christian Rüsing

The Deformation Behavior of Functionally Graded TWIP Steel under Monotonic Loading at Ambient Temperature

A processing route for the generation of functionally graded parts from steels showing twinning-induced plasticity is proposed. The procedure employing pre-deformation and local heat treatment allows for tailoring local properties with a high degree of freedom. Quasi-static tension tests revealed that no process-induced drawbacks are present, so that functionally graded parts of unprecedented performance become feasible.

Low-Cycle Fatigue Behavior of TWIP Steel - Effect of Grain Size

The effect of different grain sizes on the fatigue performance of high manganese TWIP steel (Twinning-Induced Plasticity) in the low-cycle fatigue regime was investigated. The average grain sizes in the fine grained condition were 2 5 μm and after heat treatment in the coarse grained condition about 80 μm were obtained. Pronounced twin-dislocation interactions especially in small grains strengthen the steel during monotonic deformation. Twin boundaries act as obstacles for dislocation slip, and thus, further reduce the effective grain size, which affects the fatigue response as well. The samples were monotonically and cyclically deformed at room temperature. The results reveal that the grain size has a significant influence on the mechanical as well as on the cyclic performance. Especially under cyclic loading differences in the resulting stress levels and cyclic stability can be observed. To clarify the microstructure evolution before and after fatigue with different constant strain amplitudes the samples were analyzed by means of transmission electron microscopy (TEM).