PURPOSE: To manufacture rationally a rotor shaft, in which high pressure parts and low pressure parts made of the same material are formed in one piece and which satisfy the characteristics required for the lower pressure parts by increasing its toughness, by subjecting Cr-Mo-V steel to specific heat treatment after it is shaped by forging.

CONSTITUTION: Cr-Mo-V steel is melted, cast, and is shaped by forging into a shaft blank. Said blank is subjected to the primary hardening, then its high pressure parts are subjected to the secondary hardening at 950W1,000°C temp. and its low pressure parts at Ac1WAc3 temp. The whole blank is then subjected at least to one run of temperature at 600W750°C temp. This method allows to manufacture a rotor shaft, in which high pressure and low pressure parts are formed in one piece, and which has prescribed hardness at the high pressure parts, and excellent toughness at the low pressure parts.