Abstract: 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.

Abstract: A steel blade for turbomachinery, for example, a vane or blade of stainless steel for a steam turbine, has its working surface smoothed, for example, by tumble polishing, to a smoothness of about 0.25 microns Ra or less. Then the smoothed surface is subjected to plasma nitriding to harden the surface to a value of, for example, about 1000 on the Vickers hardness scale. The hardened nitrided layer in the steel can be 25 to 100 microns thick. The plasma nitriding process does not affect the smoothness of the area of surface being nitrided, and the resultant surface hardness preserves smoothness of the surface while the blade is in use.