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China Low Activation Martensitic (CLAM) steel as one of 9%Cr ferritic-martensitic steels was designed as the structural materials for fusion reactors and lead-based Reactor in China. The long-term thermal stability of precipitated phases in CLAM steel at 550 °C was systematically studied in this paper, including coarsening kinetics, number density and shape stability. Based on large data statistics, the coarsening kinetics of M 23 C 6 carbide, MX carbonitride and Laves phase were analyzed to develop a coarsening model of each precipitated phase, respectively. The results showed that the coarsening rate of Laves phase was about 100 times than that of M 23 C 6 carbide after aging for 20,000 h at 550 °C. The number density of precipitated phases increased firstly and then decreased with increasing of aging time due to a dynamic equilibrium process of the precipitation and dissolution of precipitated phase. The results will help to deep understand degradation mechanisms after thermal aging. [ABSTRACT FROM AUTHOR]

Thermal aging experiment is an effective method to evaluate the thermostability of structure materials which serve in high temperatures. But it difficult to acquire the aging data throughout service term, because it would take a long time. Hence, an accelerating thermal aging model of China low activation martensitic (CLAM) steel was built in this paper to shorten the time of the thermal aging experiment. The microstructure analysis and Charpy impact tests were conducted on CLAM steel after thermal aging with different temperatures. The results showed that raising temperature could accelerate the grain coarsening process and the main factor of ductile-to-brittle transition temperature (DBTT) increasing was grain coarsening after aging for less than 8000 h which were analyzed by fracture model. Hence, the activation energy of grain coarsening with a value of 47.4 kJ/mol could be regarded as the activation energy of thermal aging. Then a model of accelerating thermal aging was built by using Arrhenius formula to evaluate the properties degradation during thermal aging. This strategy could be used to accelerate thermal aging process of CLAM steel through raising aging temperature and it could save time and cost for aging experiment. [ABSTRACT FROM AUTHOR]