Prolonged creep lifetime of ferritic self-healing steels achieved by offline healing treatment

Abstract

For the ferritic self-healing (FSH) steel, it remains challenging to solve the low healing efficiency problem, due to the mismatch between the formation kinetics of creep cavities and the precipitation kinetics of healing agents. In this research, an offline healing treatment has been proposed to stimulate the formation of the Laves phase precipitates as self-healing agents to retard creep cavity growth at elevated temperatures. The corresponding treatment parameters were determined by the precipitation behaviors of Laves phases on the external free surfaces and internal cavity surfaces of FSH steels. Results have shown that the creep lifetime of the offline healing treated samples can be extended more than 30% compared to that of non-healed sample, while the creep rates can be reduced by one order of magnitude. The formation kinetics of Laves phases and creep cavities have been quantitatively analyzed. It was found that after the offline healing treatments, the average cavity sizes of the samples decreased significantly, while the growth rates of creep cavities rather than the nucleation kinetics are compensated by the healing phenomena of Laves phase formation. The relationship between the extended lifetime and filling ratios of creep cavities by the healing agents was established as well. The demonstrated potential of offline healing treatments provides a new strategy to cultivate the self-healing capabilities of heat resistant steels.