2019 Volume 60 Issue 4 Pages 495-502
Quantitative mechanical analyses by nano indentation were performed for two types of ferritic heat-resisting steel that contained 12 mass% chromium and 2 mass% tungsten (12Cr–2W). One of the 12Cr–2W with a superior creep-fatigue property showed transgranular fractures, whereas the other steel with an inferior creep-fatigue property did intergranular fractures. In the inferior steel, coarse subgrains in the coarse blocks neighboring the prior austenite grain boundaries were formed during the creep-fatigue testing. Nano-scale hardness of the coarse subgrains or blocks neighboring the grain boundaries were markedly lower than those of the fine blocks far from the grain boundaries after the creep-fatigue test. Moreover, a pop-in behavior (in the relationship between force and penetration depth) occurred at only the coarse blocks neighboring the prior austenite grain boundaries. The pop-in behavior indicates that the dislocation density in the coarse blocks should be extremely lower by the recovery or rearrangement of dislocation by the creep-fatigue process at high-temperature. Therefore local deformations were assisted in the coarse blocks neighboring to grain boundaries and introduce the intergranular fractures.
This Paper was Originally Published in Japanese in J. Soc. Mater. Sci., Japan 66 (2017) 887–892.
