Ni-base alloy for turbine rotor of steam turbine and turbine rotor of steam turbine

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2008-092782 filed on Mar. 31, 2008; the entire contents of which are incorporated herein by reference.

1. Field of the Invention

The present invention relates to a material configuring a turbine rotor of a steam turbine into which high-temperature steam flows as a working fluid, and more particularly to an Ni-base alloy for a turbine rotor of a steam turbine excelling in high-temperature strength and the like, and a turbine rotor of a steam turbine made of the Ni-base alloy.

2. Description of the Related Art

For a thermal power plant including a steam turbine, a technology for suppression of the emission of carbon dioxide is being watched with interest in view of the global environmental protection, and needs for highly efficient power generation are increasing.

To increase the power generation efficiency of the steam turbine, it is effective to raise the turbine steam temperature to a high level, and the recent thermal power plant having the steam turbine has its steam temperature raised to 600° C. or higher. There is a tendency that the steam temperature will be increased to 650° C., and further to 700° C. in future.

A turbine rotor, in which moving blades rotated by high-temperature steam are implanted, has a high temperature by circulation of high-temperature steam and generates a high stress by rotating. Therefore, the turbine rotor is required to withstand a high temperature and a high stress, and a material configuring the turbine rotor is demanded to have excellent strength, ductility and toughness in a range of room temperature to a high temperature.

Particularly, if the steam temperature exceeds 700° C., a conventional iron-based material is poor in high-temperature strength, so that the application of the Ni-base alloy is considered in for example JP-A 7-150277(KOKAI).

The Ni-base alloy has been applied extensively as a material mainly for jet engines and gas turbines because it is excellent in high-temperature strength and corrosion resistance. As its typical examples, Inconel 617 alloy (manufactured by Special Metals Corporation) and Inconel 706 alloy (manufactured by Special Metals Corporation) have been used.

As a mechanism to enhance the high-temperature strength of the Ni-base alloy, Al and Ti are added to secure the high-temperature strength by precipitating a precipitated phase called as a gamma prime phase (Ni₃(Al, Ti)) or a gamma double prime phase, or both of them within the mother phase material of the Ni-base alloy. There is for example Inconel 706 alloy which secures high-temperature strength by precipitating both the gamma prime phase and the gamma double prime phase.

Meanwhile, the high-temperature strength of Inconel 617 alloy is secured by reinforcing (solid-solution strengthening) the mother phase of Ni group by adding Co and Mo. For example, JP-A 2002-88455(KOKAI) and JP-A 2001-247942(KOKAI) disclose a Ni-base alloy having high-temperature strength characteristic improved by adjusting added element components based on the components of Inconel alloy. The Ni-base alloy of JP-A 2002-88455(KOKAI) is provided with improved sulfidation corrosion at a high temperature. JP-A 2001-247942(KOKAI) describes a rotor shaft using a Ni-base alloy which suppresses a fragile intermetallic compound formed when used for a long time.

Since the above-described conventional Ni-base alloys are poor in productivity, they were used for relatively small high-temperature parts and the like only.

Therefore, in a case where the conventional Ni-base alloy is applied to, for example, jet engine or gas turbine members, portions where the Ni-base alloy is used are limited to small blades having a length of less than 1 m, a disk material having a gross weight of less than 1 ton or the like.

Accordingly, the present invention provides an Ni-base alloy for a turbine rotor of a steam turbine that workability such as forgeability is excellent, and a large-size forged product turbine rotor can be produced, and a turbine rotor of a steam turbine.

According to an aspect of the invention, there is provided an Ni-base alloy for a turbine rotor of a steam turbine, which contains in percent by weight C: 0.05 to 0.15, Cr: 22 to 28, Co: 10 to 22, Mo: 8 to 12, Al: 0.8 to less than 1.5, Ti: 0.1 to 0.6, B: 0.001 to 0.006, Re: 0.1 to 2.5, and the balance of Ni and unavoidable impurities.

According to an aspect of the invention, there is also provided a turbine rotor which is disposed through a steam turbine into which high-temperature steam is introduced, wherein at least a predetermined portion is formed of the Ni-base alloy for the turbine rotor of a steam turbine described above.

Embodiments of the invention will be described below.