Achieving long-term stability of the tempered martensite is considered crucial for increasing the creep resistance of steels at elevated temperatures above 700°C. It is noted that at low stress levels, the creep deformation of the tempered martensite proceeds heterogeneously around prior austenite grain boundaries, as excess dislocations inside the grain are difficult to rearrange. This paper presents a new approach using carbon-free martensitic alloys strengthened by intermetallic compounds. An iron-nickel-cobalt martensite matrix with Laves phase as the precipitate is selected. The creep characteristics are discussed across a wide range of testing conditions, and the thermal cycle test behavior is examined to evaluate the potential of these alloys for future ultrasupercritical power plants operating in severe environments.

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