Disappearance of Martensitic Strengthened-Micro-Texture in Modified 9Cr-1Mo Steel Caused by Stress-Induced Acceleration of Atomic Diffusion at Elevated Temperatures
Modified 9Cr-1Mo steel is a heat-resistant steel developed for a steam generator in a FBR (Fast Breeder Reactor) and it has been applied to various thermal power plants. Recently, it was found that the fatigue limits did not appear up to 108 cycles at temperatures higher than 500oC. The reason for the decrease of the fatigue life was attributed to the change of the initially designed microstructure of the alloy. The initially dispersed fine lath martensitic texture disappeared at temperatures higher than 500°C, when the magnitude of the applied stress exceeded a certain critical value. In order to explicate the dominant factors of the change quantitatively, the change of the microstructure and the strength of the alloy were continuously observed by applying an intermittent fatigue and creep tests at elevated temperatures and EBSD analysis. It was found that there was a critical stress which caused the microstructure change at each test temperature higher than 500°C, and the activation energy of the change was determined as a function of temperature and the applied tensile stress. The dominant factor of the micro structure change was the stress-induced acceleration of the atomic diffusion of the component element of the alloy.
Luis Rodríguez-Tembleque, Jaime Domínguez and Ferri M.H. Aliabadi
T. Shinozaki et al., "Disappearance of Martensitic Strengthened-Micro-Texture in Modified 9Cr-1Mo Steel Caused by Stress-Induced Acceleration of Atomic Diffusion at Elevated Temperatures", Key Engineering Materials, Vol. 774, pp. 31-35, 2018