ROLE OF DRAWING-INDUCED RESIDUAL STRESSES AND STRAINS ON HYDROGEN EMBRITTLEMENT OF COLD DRAWN WIRES

Hydrogen embrittlement (HE) plays an important role in the environmental cracking of cold drawn prestressing 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 generated in the vicinity of the wire surface during the manufacturing (cold drawing) process.
Previous research [1] established an important milestone by obtaining a quantitative relationship between the level of residual stress and the fracture behaviour of cold-drawn prestressing steel wires under HE conditions. This paper goes further in the analysis, so that the earlier developed computer model [1] is advanced [2-6] and applied to analyse the influence of the residual stress-and-strain profiles after cold drawing on the HE susceptibility of prestressing steel. Firstly, the drawing process is modelled to obtain the distributions of residual stress and strain. Later, a model of hydrogen diffusion assisted by stress-and-strain is applied to compute the concentrations of hydrogen. Numerical results shows the relevant role of residual stress and strain field in hydrogen diffusion in the samples, as well as the differences between short and long exposure times.
[1] Toribio, J and Elices, M., Int. J. Solids Structures, 28, 791-803, 1991.
[2] Toribio, J. and Kharin, V., Fatigue Fract. Engng. Mater. Structures, 20, 729-745, 1997. 
[3] Toribio, J. and Kharin, V., Nuclear Engng. Design, 182, 149-163, 1998.
[4] Toribio, J. and Kharin, V., Int. J. Fracture, 88, 233-245, 1998.
[5] Toribio, J. and Kharin, V., Int. J. Fracture, 88, 247-258, 1998.
[6] Toribio, J. and Kharin, V., Fusion Engng. Design, 51-52, 213-218, 2000.