A metallographic and fractographic study of the origin of cleavage fracture in mild steel

The scanning electron microscope was used to study the morphology of fracture surfaces and the metallography of sections just below fracture surfaces for a mild steel tested in simple tension and notch bending. Scanning electron microscope observations indicated that the nucleation and propagation of cleavage cracks are controlled by a stochastic process characteristic of the microstructural features and, hence, a probabilistic requirement is to be met. The fracture micromechanism was clarified through distinguishing between the “cleavage fracture origin” and the “initial cleavage crack.”