Effect of the hydrogen outgassing time on the hardness of austenitic stainless steels welds

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 H2SO4 containing 100 mg l−1 of As2O3. 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.