Rosette fracture of modified 9Cr-1Mo steel in tension

Rosette fracture is a typical mode of tensile fracture with long radial cracks. This type of fracture was observed in the modified 9Cr-1Mo steel in normalized and tempered condition on tensile testing at room temperature (RT). The role of different variables such as temperature, microstructure, strain rate, texture and plastic constraint was studied on the rosette fracture occurring from tensile testing of the modified 9Cr-1Mo steel. Radial cracks were observed on the fracture surface at different angular intervals. These cracks propagated longitudinally and were mostly associated with prior austenite grain boundaries and lath boundaries. Rosette fracture was found to be affected by test temperature, microstructure (in particular the number density, size and distribution of carbide precipitates along the prior austenite grain boundaries/lath boundaries) and the plastic constraint; however, there was no effect of texture. The tendency and severity of rosette fracture were found to be affected by the heat treatment and resulting area fraction of carbides. The process of rosette fracture was found to be associated with void formation at carbide particles, lying at the prior austenite grain boundaries and lath boundaries and their rapid linkage along the boundaries oriented with stress axis.