Fracture characteristics of thermally exposed 9Cr-1Mo steel after tensile and impact testing at room temperature

The paper deals with the fracture analysis of thermally exposed 9Cr-1Mo ferritic steel after tensile and impact testing at room temperature. The temperatures of the thermal expositions were 580, 620, and 650 degrees C, respectively. The duration of annealing experiments varied from 500 to 5000 h. The influence of thermal expositions on Vickers hardness as well as tensile properties was found to be negligible. On the other hand, remarkable effects of the annealing on room temperature impact toughness were observed. Fracture behaviour of the 9Cr-1Mo steel is strongly affected by the presence of precipitates of secondary phases. Fracture surfaces of tensile samples indicate mainly transgranular dimple fracture mechanism. By contrast, the fracture mode of the samples after impact testing is more complex. It shows both - ductile dimple tearing as well as inter-lath decohesion. (C) 2008 Elsevier Ltd. All rights reserved.