EVALUATION OF THRESHOLD STRESS INTENSITY IN HIGH-STRENGTH HYDROGEN CHARGED STEEL IN LOW STRAIN-RATE TENSION TESTS

The fracture ductility of high strength steel is strongly influenced by the presence of hydrogen, although hydrogen does not significantly affect the yield strength. The deterioration of fracture ductility is particularly evident in low strain rate tension tests, but less pronounced at conventional crosshead speeds. Low concentrations of hydrogen in high strength steels do not substantially affect the fracture toughness, but result in the appearance of a threshold stress intensity. The threshold values can be obtained from low strain rate tension tests at a crosshead speed of 0.1 mm min-1. These values are practically the same as those obtained from hydrogen charged peripherally notched precracked specimens subjected to a constant static load in a delayed failure test. Microfractographic investigations of fracture surfaces of hydrogen charged steel from low strain rate tension tests indicate that the growth and the coalescence of voids in the final stages of the fracture process are partly assisted by the decohesion of interfaces on which hydrogen is adsorbed. (C) 1993 The Institute of Materials.