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Hydrogen effects in austenitic steels submitted to fatigue tests have been studied. Superficial H was introduced cathodically at 50 °C using 1N H2SO4 solution, a platinum counter electrode and a current density of 1000 A/m2 during 4 h. Internal H was introduced cathodically using a mixture of the salts KHSO4 and NaHSO4 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.

Hydrogenation effects on the nanohardness of 304L/308L austenitic stainless steel joints have been studied. Surface cracks and α′ martensitic phase are nucleated during aging at room temperature (RT) and the nucleation kinetic depends on the hydrogen (H) outgassing time. Since these effects are confined on the superficial layers of the material, nanoindentation test is a powerful tool to analyze the region modified by H. The hydrogenation was performed cathodically at RT, during 4 h, using an electrolyte of 1 N H 2 SO 4 containing 100 mg l −1 of As 2 O 3 . A platinum counter electrode and a current density of 1000 A m −2 were used. In this work nanoindentation tests were performed as soon as the hydrogenation was interrupted and with the outgassing time varying up from hours to some days. It was observed that nanohardness have high values in the base and weld metal (WM) just after the hydrogenation process have been interrupted and that decreases with H outgassing time. After several days of outgassing time it was observed a significant decrease in hardness of base metal (BM) and WM when compared with a material without H.