Abstract
Hydrogen Induced Fracture (HIF) plays an important role in the environmental cracking of cold drawn prestressings steel wires. The Standard Test in Ammonium Thiocyanate was proposed by the International Federation of Prestressing (FIP) as a suitable experimental method for checking the susceptibility of high-strength prestressing steels to hydrogen embrittlement. However, the FIP tests usually exhibit a high scattering of the results. It can be caused by the distribution of residual stresses and strains generated in the vicinity of the wire surface during the manufacturing (cold drawing) process. To this end, the knowledge of residual stresses and plastic strains in wires due to cold-drawing, as well as of wires hydrogenation from harsh environments, are the key to successful predictions of wire lives. Thus, the aim of this work is to improve previous analyses of HIF in cold-drawn prestressing wires via numerical modelling, first, comparing the distributions of residual stresses and plastic strains due to different real drawing processes, and next, analyzing the stress-strain assisted hydrogen diffusion in wires towards creation of the conditions for HIF nucleation. In order to achieve this goal, two industrial cold-drawing processes are analyzed. Basically the main differences between both are (i) the reduction of cross-sectional area performed at first drawing stage and (ii) the number of drawing steps used in the whole process. Generated results prove the importance of an adequate design of the cold drawing process with regard to the residual stress-and-strain field and its relevant role in hydrogen diffusion in the wires, as well as its possible consequences for HIF.
