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Abstract
The effect of non-metallic inclusions on cleavage in wrought steel has been studied using a resulphurized mild steel. The cleavage fracture stress was measured at –196°C and found to exhibit an orientation dependence which is attributed to the morphology of the inclusions. In the short transverse and transverse testing orientations, cleavage facets were seen to initiate at the edges of the elongated inclusions. It is proposed that the inclusions do not themselves act as cleavage crack nuclei, but are internal sites of stress concentration that facilitate carbide-initiated cleavage in the adjacent matrix. In the longitudinal testing orientation, inclusions are not associated with sites of cleavage nucleation. It is proposed that in this orientation decohesion of the inclusion/matrix interface causes a reduction in stress triaxiality which inhibits cleavage nucleation. Measurements of fracture toughness K1c at –196°C show no effect of testing orientation. This is attributed to the low probability of encountering inclusions in the crack tip process zone under the conditions of testing.
MST/365
