ROLE OF MICROSTRUCTURAL ANISOTROPY OF PRESTRESSING STEEL ON THE FRACTOGRAPHIC APPEARANCE OF HYDROGEN-ASSISTED MICRO-DAMAGE

摘要

Cold drawn prestressing steel wires are materials with a markedly oriented microstructure as aconsequence of the manufacturing (cold drawing) process. In addition, it is well known that suchmaterials usually work in harsh (or aggressive) environments and they are highly susceptible toenvironmentally assisted cracking (EAC) in general, either pure stress corrosion cracking (SCC) bylocalized anodic dissolution (LAD) or the even more dangerous phenomenon of hydrogen assistedcracking (HAC), hydrogen assisted fracture (HAF) or hydrogen embrittlement (HE). This study analyzesthe influence of microstructural anisotropy of prestressing steel wires on a special fractographyassociated 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 constantextension rate tests (CERT) up to fracture are analyzed, in an environment causing HAF. Generatedresults show that, in materials with microstructural anisotropy, the fracture surface with TTS fractographytends to take the form of lined up humps ascending a sloped plane. Furthermore, this study provesthat hydrogen enhances the effect of microstructural anisotropy of material on the fracture surface.