Stress corrosion cracking behaviour of colddrawn and stress-relieved prestressing steel of standard
quality conforming to IS. 1785- Part I has been studied in H2S saturated aqueous solution with and
w~thout chloride. The steel was found to be highly susceptible to cracking even under open circuit
condition at room temperature.The suscept~b~litdye creased slightly with temperature in the range 3O0C-
80°C. The threshold stress was found to increase with pH of the medium from 15%of proof stress at pH
2.6 to 40 %of proof stress at pH 6.5. A limiting pH of 7 above which stress corrosion cracking did not occur
was obtained for water- H2S system and the corresponding value in 3.5PbNaCI- H2S system was found
to be 9. Cathodic polar~sationd ecreased the time to failure while anodic polarisation increased the time to
failure. Application of tensile stress was,found to increase the corrosion rate and also the solubility of
hydrogen. The strain rate was found to have profound influence on the cracking process and the susceptihlity
was h~gha t very low stram rates. SEM fractographic studies revealed that the fracture mode was
predominantly intergranular. All these observations could be understood in terms of a decohesion mode
