Fracture Mechanism of a Bainite Steel in Precracked and Notched Specimens at Low Temperature

Precracked and notched specimens were used to investigate the fracture mechanism of a bainite steel at low temperature. The critical fracture event was studied using metallographic sectioning method. The results showed that the critical cleavage event was different in the precracked and the notched specimens. At -196C, all specimens fractured at lower-shelf region without any ductile crack growth. The critical crack tip opening displacement was not sensitive to the depth of precrack. With increasing temperature to –100C, cleavage was preceded by ductile crack growth for all precracked specimens. A longer ductile crack growth was associated with the shallow crack specimens, which resulted in a higher critical crack tip opening displacement. The ratio of depth to width of micro-dimple on ductile crack surface was decreased with ductile crack growth.