Among HEA alloys, the CoCrFeMnNi system is probably one of most studied. In this work, different alloys from this system have been investigated. Modifications of the classic equiatomic chemical composition have been proposed on the basis of Thermocalc calculations. The so-determined compositions have been cast and forged or rolled. This work led to the formulation of an optimal proportion of the five elements, called A3S grade (austenitic super stainless steels). At room temperature, yield strength above 800 MPa with a fracture elongation of 35 % could be obtained in forged alloys. When cold rolled, the alloys show yield strength of above 1300 MPa with still significant ductility. Moreover, the deformed microstructure is stable up to high temperatures, and the recovery starts only after 50h at 550°C. Finally, the A3S grade conserves a ductile austenitic structure even at LN2 temperature; in these conditions, impact toughness above 120 J/cm² was measured.