The relationship between microstructure evolution and impact toughness degeneration of alloy 617B during long term aging

Impact toughness degeneration and microstructure evolution of alloy 617B during 650-725 degrees C long-term aging for up to 12,000 h were investigated in present work. It is found that impact toughness decreases apparently even after just 20 h aging in the temperature range of 650-725 degrees C and keeps decreasing with prolonging aging time. Hence, detailed microstructure observation and mechanical property tests were carried out to reveal the essence of impact toughness degeneration during long-term aging. And the reason is confirmed to be the combination effect of plasticity evolution and grain boundary carbide coarsening. The degeneration of impact toughness with prolonging aging time can be divided into rapid decrease stage, slow decrease stage and stable stage. The decrease of plasticity in the major reason for rapid impact toughness degeneration in the initial stage of aging. Grain boundary carbide coarsens obviously during aging and tends to be continuous. This is the major reason for the slow and continuous decrease of impact toughness in the slow decrease stage. Finally, plasticity and grain boundary carbide change little, resulting in the stable stage of impact toughness evolution. Enough attention should be paid on impact toughness degeneration in the evaluation of long-term stability. (c) 2022 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Superscript/Subscript Available

Automated summary

The present study investigated the impact toughness degeneration and microstructure evolution of alloy 617B during long-term aging at temperatures of 650-725 degrees Celsius for up to 12,000 hours. It was found that the impact toughness decreases significantly even after just 20 hours of aging within the temperature range, and it continues to decrease as the aging time prolongs. The degeneration of impact toughness is attributed to the combined effect of plasticity evolution and grain boundary carbide coarsening. The degeneration process can be divided into rapid decrease stage, slow decrease stage, and stable stage. Sufficient attention should be paid to the impact toughness degeneration when evaluating long-term stability.