A steam turbine rotor has at least a first stage and a last stage. The rotor is optimised for operation in a wet steam environment at steam temperatures of less than 300° C. by being made more resistant to stress corrosion cracking (SCC). The yield strength of the rotor varies along its axial length such that the yield strength of the rotor in the region of the last turbine stage is more than the yield strength of the rotor in the region of at least one earlier turbine stage.