Abstract: A steam turbine (10) has an impulse rotor (11), a multiplicity of stages (N, . . . , N+4) which are arranged in series along a machine axis (12) and with each of which is associated a wheel disk (11a-e) equipped with corresponding rotor blades (17a-e). The rotor blades (17a-e) of the individual stages (N, . . . , N+4) project into a common axial steam passage (15) into which steam (14) enters via an inlet duct (13), and diaphragms (16b-e) are arranged between the stages (N, . . . , N+4) in each case. A simple and effective protection of the wheel disks against stress corrosion cracking is achieved by dry superheated steam (14) being fed to the steam turbine (10), and for reducing or for avoiding stress corrosion cracking on wheel disks (11b-e) of the impulse rotor (11) which are exposed to the risks of wet steam, by the dry superheated steam (14) being used for purging of the wheel disks (11b-e) of the impulse rotor (11) which are at risk.