A method for manufacturing a turbine rotor (a shaft body) constituting a steam turbine by preparing a plurality of divided shaft members and welding and joining the divided shaft members together is known (for example, refer to Patent Literature 1). According to such a method, different materials can be applied to each of the shaft members, and materials of the shaft members can be selected in accordance with a temperature distribution in the steam turbine.
When a turbine rotor includes three members divided from each other in an axial direction thereof, material selection, in which a high Cr steel with excellent high temperature strength is used as a base material of a central portion disposed at a position at which an ambient temperature in a steam turbine is in a high temperature region and low alloy steels are used at other sites, can be performed.
In such a manufacturing method, post weld heat treatment (PWHT) is generally performed for the purpose of securing toughness of a welding metal formed between adjacent shaft member and decreasing hardness of a welded heat affected zone (a heat-affected zone; HAZ).
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