Role of Microstructural Anisotropy of Prestressing Steel on the Fractographic Appearance of Hydrogen-Assisted Micro-Damage

Cold drawn prestressing steel wires are materials with a markedly oriented microstructure as a consequence of the manufacturing (cold drawing) process. In addition, it is well known that such materials usually work in harsh (or aggressive) environments and they are highly susceptible to environmentally assisted cracking (EAC) in general, either pure stress corrosion cracking (SCC) by localized anodic dissolution (LAD) under anodic conditions or the even more dangerous phenomenon of hydrogen assisted cracking (HAC), hydrogen assited fracture (HAF) or hydrogen embrittlement (HE) when hydrogen appears due to cathodic protection (the case of cathodic overprotection being specially dangerous) or due to local electrochemical conditions in the close vicinity of the crack tip.

This study analyzes the influence of microstructural anisotropy of prestressing steel wires on a special fractography associated with hydrogen-assisted micro-damage in pearlite, the so called tearing topography surface (TTS). To this end, fracture surfaces of notched specimens of pearlitic steels subjected to constant extension rate tests (CERT) up to fracture are analyzed, in an environment causing HAF. Generated results show that, in materials with microstructural anisotropy, the fracture surface with TTS fractography tends to take the form of lined up humps ascending a sloped plane. Furthermore, this study proves that hydrogen enhances the effect of microstructural anisotropy of material on the fracture surface.

Key words:

Prestressing steels, hydrogen embrittlement, microstructural orientation, strength anisotropy, cold drawing.