Environmentally assisted cracking of cold drawn eutectoid steel for civil engineering structures

The paper analyzes the environmentally assisted cracking behaviour of eutectoid steels with different degrees of cold drawing subjected to electrochemical conditions promoting localized anodic dissolution. The experimental results showed a progressively anisotropic behaviour as the degree of cold drawing increases, with an evolution in the fracture type from Mode I (isotropic behaviour in slightly drawn steels) to mixed mode propagation (strongly anisotropic behaviour in heavily drawn steels). The fractographic analysis revealed changes in the microscopic topography depending on the fracture propagation mode. The phenomenon of crack tip blunting by selective dissolution in the near-tip area is discussed and the blunting effect increases with the degree of cold drawing. Attention is also paid to the possibility of evolution from smooth blunting to cornered blunting associated with shear at the crack tip vertices, so the markedly oriented pearlitic microstructure favours cornered blunting in the most heavily drawn steels.