The tensile and cyclic deformation behaviour of a new metastable austenitic stainless cast steel were studied in-situ in a scanning electron microscope (SEM). The metastable steel was investigated in cast condition. The in-situ tests in the SEM show the evolution of the microstructure in dependence on the deformation degree for uniaxial deformation and the number of cycles during fatigue, respectively. The development of the microstructure (i.e. deformation bands) are correlated with the places, where the phase transformation of the metastable austenite into the hcp structure or the bcc ’- martensite (TRIP – effect; TRansformation Induced Plasticity) takes place by applying different SEM-techniques as electron backscatter diffraction (EBSD). In addition, calculations of local deformation fields developing during tensile and cyclic deformation using digital image correlation (DIC) are presented.