Short cracks can grow faster than long cracks. Further they cab grow under the threshold value of long cracks. Usually for short cracks no unique relation exists between crack propagation rate and stress intensity range. This work deals with all 3 kinds of short cracks, physically, mechanically and microstructurally short cracks. The tested material was an austenitic steel (A220) with different microstructures. The tension compression samples were notched with a razor-blade and with the FIB a crack-like notch was milled. With in-situ experiments in the SEM the influence of the initial crack length, the correlation of the crack length to the grain size and the development of the crack growth rate with rising crack length were studied. In summary a relation between the crack growth rate, the cyclic crack tip opening displacement and crack length could be found for mechanically short cracks. With microstructurally short cracks a similar behaviour could be observed. However in this case exists no simple relation between strain amplitude and crack tip deformation.