This paper summarizes the achievements of a major research line at tht Materials Science Department of the University of La Coruna (Spain) in the field of environmentally assisted cracking in general and hydrogen degradation in particular. It deals with a materials science approach to the study of corrosion assisted cracking of progressively drawn pearlitic steels for civil engineering use. The approach is based on the fundamental idea of materials science: linking the microstructure of the different steels (progressively oriented as a consequence of the manufacture process by cold drawing) with their macroscopic stress-corrosion behaviour (increasingly anisotropic as the degree of cold drawing increases). The first part of the researth was the metallographic analysis. Attention was paid to the evolution with cold drawing of the two basic microstructural levels: the pearlite colonies (first level) and the pearlitic lamellae (second level). With regard to the first microstructural level, a progressive elongation and orientation of the pearlitic colonies in the cold drawing direction (wire axis) was observed. In hte matter of the second microstructural level, the analysis showed an increasing closeness of packing (with decrease of the interlamellar spacing) and a progressive orientation of the pearlitic lamellar microstructure in the cold drawing direction. Therefore, both pearlite colonies and pearlitic lamellar microstructure tend to align to a direction quasi-parallel to the wire axis as cold drawing proceeds. The second part of the research consisted of a programme of stress corrosion cracking tests under both cathodic and

anodic conditions to promote two very different mechanisms of cracking: hydrogen assisted cracking (HAC) and localized anodic dissolution (LAD). Both types of stress corrosion test confirm that the cold drawn steels exhibit anisotropic behaviour associated with a clear change in crack propagation direction which approaches the wire axis or cold drawing direction. For both regimes (NAC and LAD) there is a strong correlation between the microstructural orientation angles (at the two levels of pearlitic colonies and lamellae) and the propagation angles of the macroscopic crack, which clearly demonstrates the influence of the oriented microstructure - and thus of the manufacture process by increasing cold drawing - on the macroscopic corrosion-assisted behaviour of the steel wires.

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