Superficial and internal hydrogenation effects on the fatigue life of austenitic steels

Hydrogen effects in austenitic steels submitted to fatigue tests have been studied. Superficial H was introduced cathodically at 50 °C using 1N H 2SO 4 solution, a platinum counter electrode and a current density of 1000 A/m 2 during 4 h. Internal H was introduced cathodically using a mixture of the salts KHSO 4 and NaHSO 4 at 200 °C during 60 h by applying a constant polarization potential of 850 mV with respect to a silver reference electrode. Fatigue tests were carried out by using a alternate flexion fatigue machine with stress ratio R values equal 1 and frequency of 50 Hz. The samples were tested until the fracture of the material was reached or until the stipulated fatigue limit life was reached. Results showed that superficial H introduced surface cracks during outgassing process while internal hydrogenation did not modify the superficial conditions. Mechanical tests showed that H reduced the fatigue life of these steels, and this effect was even more accentuated at lower stresses. Superficial hydrogenation presented inter and transgranular fracture and the morphology of the fracture remained ductile while internal H presented transgranular fracture and some regions with fracture by cleavage process.