## 1 Introduction  
Fossil fuel-fired steam and gas power generation is currently supporting \(\sim\)80% of the energy supply in the world [1]. Because of the carbon dioxide emissions from the fuel combustion, however, a recent worldwide trend is to claim the need to replace fossil fuel power generation with renewable energy such as solar power and wind power as the main power source in the near future [2]. Steam and gas turbine power generation systems, however, have advantages in providing energy security, including an ability to supply energy in case of an emergency, and will also be needed in the future as an important power source while using clean fuels such as H\({}_{2}\) and NH\({}_{3}\) and/or carbon capture technologies. It is, therefore, important to continue making efforts to further increase the efficiency and the durability of turbine power generation systems, thereby improving the high temperature durability of heat-resistant steels and alloys for the systems.  
High-Cr heat-resistant ferritic steels are an important class of materials for high-temperature components such as steam pipes and turbines in high-efficiency coal-fired power plants. These steels are designed such that the ferritic matrix, inherited from the martensitic transformation, are strengthened with M\({}_{23}\)C\({}_{6}\) (M: Cr, Mo, Fe)-type carbide and (V, Nb)(C, N)-type carbonitride particles against dislocation motion, recovery and recrystallization. The carbide and carbonitride particles are, however, susceptible to particle coarsening and decomposition in the long-term creep deformation and thereby lose their strengthening effects, which is considered to be a main cause of the degradation of the long-term creep strength of the steels [3, 4].  
Laves phase is an A\({}_{2}\)B type intermetallic phase which is formed in many Fe-based alloy systems [5]. Fe\({}_{2}\)Mo and Fe\({}_{2}\)W Laves phase particles are precipitated during creep deformation within the ferritin matrix in conventional high-Cr ferritic steels [6; 7]. Laves phase particles are observed as fine particles along the lath/block boundaries and/or as coarse globular ones, depending on the type of the Laves phase and the content of the Laves phase-forming elements. Efforts to improve the creep life of ferritic steels have been made by modification of Laves phase distribution, and positive effects on the creep resistance are reported [6; 7].  
Recently, one of the present authors [8; 9] found that fine, Hf-rich particles are precipitated in a form of periodically arrayed rows in Fe-9 Cr-based alloys containing a low amount of Hf and explained that the particles are formed through interphase precipitation during phase transformation from \(\delta\)-ferrite to \(\gamma\)-austenite, followed by a phase transformation from \(\gamma\)-austenite to \(\alpha\)-ferrite. Hf-rich particles were also identified as C14 Fe\({}_{2}\)Hf-type Laves phase by diffraction pattern analysis [8]. This finding is expected to open a new precipitation route to strengthen heat-resistant ferritic steels. The objective of the present paper is to compare the effects of precipitation routes of Fe\({}_{2}\)Hf Laves phase particles on the creep rate of 9 Cr-based heat-resistant ferritic alloys.