The Micromechanisms of Cleavage Fracture and Their Relationship to Fracture Toughness in a Bainitic Low Alloy Steel

摘要

The plastic deformation and cleavage fracture of a bainitic Cr-Mo-V steel have been studied. An estimate of the cleavage fracture strength has been made using several methods. The physical meaning of the microscopical cleavage fracture strength is not clear, but it can be used in characterizing the cleavage fracture. The cleavage fracture strength can be correlated to the same factors which influence the yield strength. The characteristic distance does not correspond to any microstructural unit and it is about one order of magnitude larger than the fracture unit in bainite, which is the bainite packet. The notch root radius for the lower limit of the toughness is of the same order of magnitude as the characteristic distance. The temperature dependence of the fracture toughness has been calculated using many methods. A new approach for the estimation of the temperature dependence of the fracture toughness is proposed. This approach is based on the yielding processes at the crack tip. Finally the fracture mechanism in bainite has been studied and a model for the mechanism which considers the real bainitic microstructure is proposed.